|
|
|
|
|
|
|
|
|||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | |||||
First published online July 2, 2007
doi: 10.1242/10.1242/jcs.004481
Research Article |
1 Department of Molecular Cell Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria
2 Department of Dermatology and Venereology, Medical University of Innsbruck, 6020 Innsbruck, Austria
Author for correspondence (e-mail: gerhard.wiche{at}univie.ac.at)
Accepted 15 May 2007
 |
Summary |
|---|
 Top Summary IntroductionResultsDiscussionMaterials and MethodsReferences |
|---|
Key words: Conditional gene targeting, Epidermolysis bullosa, Hemidesmosomes, Keratinocytes, Plectin, Transepidermal water loss
|
Introduction |
|---|
|
TopSummaryIntroductionResultsDiscussionMaterials and MethodsReferences |
|---|
). In skin, as well as in cultured keratinocytes, plectin is predominantly localized at hemidesmosomes (HDs) and cell-cell borders (Andrä et al., 2003). Association of plectin with desmosomes (Eger et al., 1997) has been shown in simple epithelial cells. With an N-terminal actin-binding domain (Andrä et al., 1998), which serves also as an integrin 
4 (Int4)-binding site (Rezniczek et al., 1998), and a C-terminal intermediate filament (IF)-binding site, plectin is instrumental in the physical anchorage of keratin filaments at the hemidesmosomal complex (Rezniczek et al., 1998; Andrä et al., 1997).
In humans, mutations in the plectin gene (PLEC1) result in skin fragility, manifested as blister formation at the level of HDs (for a review, see Pfendner et al., 2005). Clinically, these blistering disorders belong to the spectrum of epidermolysis bullosa (EB) phenotypes. Most plectin mutations lead to EB-MD, a condition characterized by neonatal blistering and late onset muscular dystrophy. Recently, however, plectin mutations have also been found in EB patients with pyloric atresia (EB-PA) (Pfendner and Uitto, 2005), a combination that can lead to early postnatal demise of the affected individuals.
Plectin-deficient mice die 1-3 days after birth exhibiting skin blistering caused by disruption of basal keratinocytes, as well as myopathies in skeletal muscle and disintegration of intercalated disks in the heart (Andrä et al., 1997). Rupture of basal keratinocytes occurs in the cytoplasm just above the inner hemidesmosomal plaque structures (Andrä et al., 1997).
The early lethality of plectin-null mice precluded the analysis of possible plectin functions at later stages of postnatal development and maturation of mice. To circumvent this problem we have now generated mice with floxed plectin alleles, rendering the plectin locus susceptible to conditional elimination by Cre recombinase. We describe here the skin phenotype of a mouse line showing a complete knockout of plectin restricted to keratin 5 (KRT5; hereafter referred to as K5)-expressing epithelia. In addition, we have generated an inducible mouse model, where plectin expression can be knocked out in small patches of epidermis at the adult stage of the animal. Our analysis of these mice demonstrates the importance of plectin in mediating mechanical stress resistance of newborn and adult epidermis and offers an explanation for the early death of plectin-deficient animals.
|
Results |
|---|
|
TopSummaryIntroductionResultsDiscussionMaterials and MethodsReferences |
|---|
). To assess whether the blistering of the epidermis, or of other stratified epithelia, was causing the animals' death, we used a gene-targeting approach to create mice with a constitutive knockout of plectin in stratified epithelia, but not in other types of tissues. Our targeting vector contained single loxP sites in introns 25 and 31, so that upon conditional removal of exons 26-31, exon 25 would be spliced into exon 32, leading to a frameshift and a premature stop codon (see Fig. S1A in supplementary material). Selected ES cell clones were screened for correct recombination events by Southern blotting (Fig. S1B in supplementary material) and subsequently injected into blastocysts. After germline transmission of the targeted allele (Fig. S1C, lane 1 in supplementary material), the resulting mouse line carrying one Plecflox(neo) allele and one Plec+ allele was bred to Flp deleter mice to excise the FRT-flanked selection marker. Pups carrying the Plecflox allele were identified and then bred to homozygosity (Fig. S1C, lane 2 in supplementary material). Mice homozygous for the floxed plectin allele (Plecflox/flox) appeared to be normal indicating that the genetic manipulation had not altered the function of plectin (data not shown).
Inactivation of the plectin gene in mouse skin leads to early postnatal death, caused by severe blistering of the oral epithelium
To inactivate plectin in the skin, we crossed Plecflox/flox mice with transgenic mice expressing the Cre-recombinase under the control of the K5 promoter (Tarutani et al., 1997). Plec
/:K5-Cre (Plec/:Krt5-Cre) mice thus generated will be referred to as K5-Cre KO. They were born at the expected Mendelian ratios and died 1-3 days after birth. They showed severe skin detachment, especially on the fore- and hindlimbs (Fig. 1A,B), and in some cases around the mouth and nasal cavities; rarely, aplasia cutis of the forelimbs was also noted (not shown). The extent of phenotypic alterations exhibited before death varied among knockout mice. Most common was skin detachment at forepaws (Fig. 1A), but also large blisters reaching the size of up to 1 cm2 were found at the upper extremities and in the armpits (Fig. 1B,C). Sometimes blisters were torn open (Fig. 1B). A histological examination revealed blister formation between the dermis and the superficial epidermal layers (Fig. 1D). Furthermore, macroscopically non-visible microblisters were revealed (not shown). K5-Cre KO animals were smaller than control animals, obviously due to a reduced gain in body weight during their short life span (Fig. 1E). Plecflox/flox mice lacking the K5-Cre transgene, Plec+/flox and Plec+/+:K5-Cre mice did not show any pathological skin phenotype. Thus, Plecflox/flox mice lacking the K5-Cre transgene were used as controls. By the type of skin disorder, reduced body weight and postnatal death, K5-Cre KO mice were indistinguishable from plectin-null (Plec–/–) mice (Andrä et al., 1997). Conditional knockout mice that were nursed at least once after their birth regularly exhibited blisters in their oral cavities (Fig. 1F). A detailed analysis of serial sections covering the entire oral cavities of these mice revealed on average three to four blisters on their palates and rarely, blister formation on their tongues was observed. By contrast, no signs of epithelial detachment were detected in proximal esophagus of K5-Cre KO mice (Fig. 1G-J). Oral blistering most probably impaired the food intake of K5-Cre KO mice, so that death due to malnutrition ensued, as has been suspected in the case of plectin-null mice (Andrä et al., 1997). Newly born K5-Cre KO pups were able to suckle milk initially, as indicated by the milk patch shining through the skin of pups (data not shown) and a milk-filled gut (Fig. 1L), similar to control pups (Fig. 1K). However, after initial food intake, subsequent intake seemed to be impaired due to formed blisters, since the stomachs of still-living 2-day-old K5-Cre KO pups were always empty (Fig. 1L, inset). The presence of milk in the stomach and the intestine of K5-Cre KO pups (Fig. 1L) after food intake showed that, as in control pups (Fig. 1K), the transport of coagulated milk was not obstructed. Therefore, it could be ruled out that the mutant mice suffered from pyloric atresia, characterized by congenital obstruction of the gastric outlet.
|
3.5-fold increase in TEWL value compared to intact skin (data not shown). However, no differences in TEWL values were observed between intact skin of K5-Cre KO and control pups, demonstrating the absence of intrinsic barrier defects in K5-Cre KO mice. A histological examination of stained spots revealed microlesions at various stages of wound healing (Fig. 1O,P). Most lesions had a histological appearance similar to that shown in Fig. 1O, with a thick, acanthotic and weakly differentiated new epidermis having formed under a crust that was still covered with the old (dead) epidermis. In some lesions, a thin, multilayered sheet of keratinocytes could be seen under the crust, indicating ongoing re-epithelialization (Fig. 1P). To test whether such lesions could be induced by trauma we applied mild mechanical stress in the form of consecutive tape strippings with D-Squame disks (a procedure normally used to sequentially remove stratum corneum layers), to the back skin of newborn K5-Cre KO and control mice, followed by dye penetration assays. Indeed, we found small blue-stained spots in 10-times stripped K5-Cre KO (Fig. 1R), but not in control skin (Fig. 1Q). Histological examination of stripped K5-Cre KO skin areas showed that stripping had induced basal keratinocyte cytolysis (Fig. 1S). Moreover, a few tape strippings were often enough to induce the formation of a large blister (Fig. 1T). When stronger adhesive tape (Tesa 3M) was used, one stripping was sufficient to remove the entire epidermis of the stripped area (not shown). Together, these data demonstrated an extreme fragility of K5-Cre KO epidermis.
Highly efficient reduction of plectin levels by K5-controlled Cre expression
To examine to what extent plectin expression was reduced in the epidermis of conditional knockout compared to control animals, immunoblotting of tissue homogenates was performed. Using an antiserum recognizing all isoforms of plectin (anti-pan-plectin), only a very weak, in fact barely detectable, signal was obtained in K5-Cre KO epidermis compared with the strong signal in control tissue (Fig. 2A). This remaining signal was likely to originate from non-keratinocyte cells present in the epidermis, such as dendritic (Langerhans) cells and pigment cells (melanocytes), which are known to express a set of plectin isoforms different from that of keratinocytes (Abrahamsberg et al., 2005) (our unpublished data). In fact, when an antiserum specific to plectin 1a, the major plectin isoform found in keratinocytes (Andrä et al., 2003), was used instead of the anti-pan-plectin antiserum, not even a weak signal was detectable in epidermal tissue extracts (data not shown). As expected, in tissue extracts from the dermis of K5-Cre KO animals, reduction of plectin expression was much less dramatic (Fig. 2A). Since neither the anti-plectin 1a nor the anti-pan-plectin antiserum (both recognizing epitopes in plectin domains preceding the rod), detected proteins in K5-Cre KO tissue homogenates, that were of lower molecular mass than full-length plectin, the expression of rodless-plectin in K5-Cre KO epidermis could be ruled out.
|
allele, indicating a recombination efficiency of 100% (Fig. 2B). In K5-Cre KO dermis, however, the 15 kb wild-type signal was predominant, with an additional (lesser) signal of 9 kb (Fig. 2B). Considering that enzymatic detachment of the epidermis leaves some hair follicles embedded in the dermis (Vasioukhin et al., 1999) (our unpublished observation), it is likely that the recombination signal observed in K5-Cre KO dermis stemmed from a contamination with keratinocytes. The absence of the 9 kb mutated gene signal in both controls (epidermis and dermis) indicated that aberrant (non-Cre-mediated) recombination between the loxP sites did not occur.
Additionally, we used immunofluorescence microscopy to assess the absence of plectin from the epidermis of knockout mice (Fig. 2C). A pronounced staining of the dermo-epidermal borderline, along with a weaker staining of the cytoplasm and membranes of all epidermal keratinocytes, was detected in normal mouse skin (Fig. 2Ca) but in the corresponding K5-Cre KO tissue, staining above background was observed in only a few insular cells (arrows in Fig. 2Cb). These plectin-positive cells most likely are melanocytes (especially those between and underneath basal keratinocytes and around hair follicles) and dendritic cells (in the suprabasal keratinocyte layers) which do not express K5 (Mahrle et al., 1989), and consequently no Cre recombinase. Plectin was also absent from the oral epithelia of K5-Cre KO animals (Fig. 2Cd), whereas in the oral cavity of wild-type mice it was strongly expressed along the basal membranes of palate and tongue epithelia (Fig. 2Cc), both of which express K5 at high levels. Plectin expression was also strongly reduced in esophagus (Fig. 2Cf), where K5 is expressed at high levels (Byrne and Fuchs, 1993), but not in the pseudostratified epithelium of the trachea (Fig. S2A,B in supplementary material), where K5 expression is restricted to a small subset of airway epithelial cells (Schoch et al., 2004) (also see Fig. S2C,D in supplementary material). As expected, plectin expression in heart (Fig. 2Ch) and skeletal muscle (data not shown) of K5-Cre KO mice was not affected.
Unaltered epidermal stratification and differentiation in K5-Cre KO mice
To investigate whether plectin deficiency had any influence on skin development and differentiation we undertook a detailed immunohistological analysis of skin sections from 1-day-old K5-Cre KO and control mice. First, we assessed the expression of two major hemidesmosomal proteins, Int4, which binds directly to plectin (Rezniczek et al., 1998), and BPAG1 (also known as dystonin; Dst). As expected, the Int4 signal was found confined to the basal membrane of basal keratinocytes and the outer root sheath of hair follicles (Fig. 3A,B). Similar to plectin-null mice (Andrä et al., 1997), the Int4 signal was slightly weaker in the K5-Cre KO epidermis compared to controls (Fig. 3B). This observation was confirmed by immunoblotting data showing reduced Int4 levels in detergent resistant, keratin-containing cell fractions from trunk skin of K5-Cre KO mice (see Fig. S3B in supplementary material). In addition, in the absence of plectin the localization of Int4 seemed to be less polarized, since the protein was also found at lateral cell borders of basal keratinocytes (Fig. 3B). In blistered areas, the Int4 signal was located at blister floors, indicating disruption of basal keratinocytes at the level of the inner hemidesmosomal plaque (inset in Fig. 3B). BPAG1 staining at the basal surface membrane of K5-Cre KO keratinocytes was well preserved, although it appeared slightly more patchy than in the control samples (Fig. 3C,D). Similar to Int4, in blistered areas, the BPAG1 signal was located at the blister floor (inset in Fig. 3D). K5, the cytoskeletal binding partner of hemidesmosomal plectin, was faithfully located in the basal keratinocyte cell layer as well as in transit amplifying cells (arrow in Fig. 3E), with similar fluorescence intensities in control and K5-Cre KO specimens (Fig. 3E,F). In blisters, K5 was localized in blister roofs (inset in Fig. 3F). Regarding K6, which is normally expressed in hair follicle keratinocytes and in some basal and suprabasal keratinocytes in ridged skin (Swensson et al., 1998), we found expression in the companion layer of epidermal hair follicles without any difference between K5-Cre KO and control animals (Fig. 3G,H). However, consistent with its known upregulation under pathological and hyperproliferative conditions (Coulombe et al., 2004), K6 was found strongly upregulated in areas of K5-Cre KO fore- and hindleg tissue, where the epidermis had become detached from the dermis (Fig. 3I). Similar observations were previously reported for other mouse models of skin blistering diseases (Dowling et al., 1996; Peters et al., 2001; Raymond et al., 2005). In addition, our observation was confirmed by immunoblotting data revealing increased expression levels of K6 in knockout compared to wild-type skin (Fig. S3B).
|
Apart from HDs, actin-linked adherens junctions (AJs) and desmosomes have central functions in establishing the epithelial sheet and its polarity (Green and Gaudry, 2000). However, AJ formation appeared to be normal in K5-Cre KO epidermis as visualized using antibody (E-cadherin) and phalloidin (actin) labeling (see Fig. S4A-D in supplementary material), whereas desmoplakin staining revealed a slight reduction of desmosome structures in suprabasal epidermal cell layers of K5-Cre KO epidermis (Fig. S4E,F in supplementary material). Similar trends were observed by immunoblotting (Fig. S3B in supplementary material). However, when macroscopically intact K5-Cre KO backskin was subjected to electron microscopy, neither desmosomal structures nor anchored keratin filaments showed any abnormalities (data not shown).
Finally, we examined the differentiation capacity of knockout epidermis by tracing K10 and involucrin as early and late differentiation markers. However, no differences in the staining patterns of either K10 or involucrin were detectable in control and K5-Cre KO keratinocytes (see Fig. S5A-D in supplementary material), indicating that epidermal stratification and differentiation proceeded normally in the mutant mice.
Plectin-deficiency does not affect proliferation and survival of keratinocytes
To investigate whether plectin deficiency affects epidermal proliferation, sections of leg skin from 1-day-old wild-type and knockout mice were immunostained using antibodies to Ki-67 (see Fig. S6A,B in supplementary material). A statistical analysis carried out in nonlesional areas of interfollicular epidermis showed that similar numbers of stained cells were present per linear millimeter of basal membrane, namely 58±13.1 and 61±14.3 for wild-type and knockout, respectively (Fig. S6C in supplementary material). This result indicated that plectin deficiency did not affect proliferation of keratinocytes in vivo. We also examined the effects of plectin deficiency on apoptosis by TUNEL analysis of the skin of newborn mice. Neither K5-Cre KO basal keratinocytes, nor control cells showed signs of apoptotic cell death (Fig. S6D,E in supplementary material). Occasionally, singular TUNEL-positive cells lining the exposed epidermal surface of blister roofs were found in K5-Cre KO mice (data not shown), indicating the occurrence of some apoptotic events after epidermal detachment.
Inducible knockout of plectin in adult skin leads to increased epidermal fragility and lesional barrier defects
Since K5-Cre KO mice, similar to plectin-null mice, died within a few days after birth, they were not suitable as an animal model for studying consequences of plectin loss at later stages in life. To overcome these limitations, we employed conditional gene targeting, using the Cre-loxP recombination system with an inducible chimeric Cre-ERT recombinase that can be activated by 4-hydroxy-tamoxifen (OHT), but not by endogenous estradiol (Feil et al., 1996; Indra et al., 1999). To achieve temporally controlled somatic plectin ablation in the epidermis, we crossed mice with one floxed and one null allele (Plecflox/–) with transgenic mice expressing the chimeric Cre-ERT recombinase under the control of the bovine K5 promoter (Feil et al., 1996). Resulting mice with a Plecflox/–:K5-Cre-ERT genotype were injected intraperitoneally with 1 mg OHT per day for five consecutive days and were subjected to phenotypic analyses 2 weeks after the last injections. Southern blotting analysis showed that 35% of the floxed plectin allele was converted to the allele under these conditions (Fig. 4A).
|
To quantify any focal defects in epidermal barrier function, we measured TEWL before and during acute barrier disruption by repeated tape strippings, as described above for constitutive conditional plectin knockout mice. In addition, the amount of proteins removed by serial tape strippings was measured to analyze stratum corneum cohesion. Under basal (non-stripped) conditions, animals with induced mosaic plectin deletion did not show a difference in TEWL, compared to control animals (Fig. 4H). However, after four subsequent strippings, TEWL began to increase sharply in mice with induced plectin deletion, but only modestly in control mice (Fig. 4H). No differences in TEWL could be observed between non-induced Plecflox/–:K5-Cre-ERTand non-induced Plecflox/flox:K5-Cre-ERT mice either under basal conditions or after tape stripping (data not shown). Estimates of the amount of proteins removed after each stripping demonstrated that during the last strippings proportionally more cells had been removed from the skin of mice with induced mosaic plectin deletion compared to control mice, suggesting increased fragility of the cell layers adjacent to the induced lesions (Fig. 4I). Overall, the data obtained with the inducible mouse model demonstrated that even localized plectin deficiency in the epidermis renders keratinocytes more prone to mechanical stress-inflicted damage.
|
Discussion |
|---|
|
TopSummaryIntroductionResultsDiscussionMaterials and MethodsReferences |
|---|
) where they were related to localized acantholysis. Small Toluidine-Blue-stained lesions were also found in the skin of K5 knockout mice, where they were attributed to cytolysis of basal keratinocytes (Peters et al., 2001). The early onset of blister formation and the severity of tissue fragility clearly showed that plectin is more important than BPAG1 in linking keratin filaments to hemidesmosomes, as BPAG1 knockout mice grow to adulthood and display only mild blistering (Guo et al., 1995). Apart from the formation of blisters and lesions due to epidermal detachment, the epidermis of K5-Cre KO displayed a normal stratified organization and correct expression patterns of differentiation markers, and proliferation and survival of keratinocytes were unaffected. The occasional presence of apoptotic cells in the lumen-proximal keratinocyte layer of blister roofs indicated that, although cytolysis due to keratinocyte disruption above the HDs predominated, some still intact keratinocytes underwent programmed cell death. However, massive apoptosis of basal keratinocytes, as it was observed upon epidermal detachment in Int4-deficient mice (Dowling et al., 1996; DiPersio et al., 2003), was not evident.
The skin phenotype of K5-Cre KO mice resembled that of children suffering from EB-PA (EB-PA; OMIM accession no. 226730), who are born with an extremely fragile skin (Charlesworth et al., 2003; Pfendner and Uitto, 2005). As most of these patients harbored premature termination codon or nonsense mutations in exons encoding N-terminal parts of the protein, a rapid decay of the prematurely terminated short RNA transcripts formed is very likely, leading to a complete absence of the protein (Charlesworth et al., 2003). EB-PA mutations being located upstream of exon 31 [the exon encoding plectin's rod domain (Liu et al., 1996)] could therefore not be compensated for by rodless plectin isoforms, explaining the more severe phenotype of patients with plectin-associated EB-PA, compared with patients suffering from EB-MD. Thus, mice with a specific deletion of plectin in stratified epithelia, such as our K5-Cre KO mice, can be considered as an ideal model for the stratified epithelia phenotypes of patients with severe forms of plectin-associated EB-PA.
Before dying, K5-Cre KO mice became progressively weaker, ceased to grow and apparently became unable to suckle, as their stomachs remained empty. Inspection of the oral cavities of newborn K5-Cre KO mice after at least one nursing showed the presence of multiple blisters on their palates and in some cases also on their tongues. Therefore, we reason that the mechanical stress applied to the oral epithelia by sucking and swallowing was the cause of the oral blister formation. As a consequence, the pups' desire for food was probably reduced due to pain and possibly obstruction of the oral cavity by especially large blisters or cellular debris. A similar runting due to prevention of feeding by erosive mucosal blistering was described for mice lacking desmoglein 3 (Koch et al., 1997). In these mice, lesions were initially caused by sucking and became even worse when growing mice began eating solid food. The finding that K5-Cre KO mice did not show epithelial detachment in the esophagus was not surprising, as the liquid diet of neonatal mice exerts only low mechanical stress on such organs.
Mucosal involvement is common in various forms of EB and cases of mucosal blistering associated with EB-MD (OMIM accession no. 226670) have been described (Kunz et al., 2000; Schara et al., 2004). The mouth and throat problems of patients suffering from EB have been reported to often cause a serious disruption of nutrient intake, similar to what we observed with K5-Cre KO mice. Because of oral blistering these children barely grow, as there is a higher need for nutrients because the body loses proteins along with the wound exudate and also has to sustain normal metabolism (information available at the DEBRA website: www.debra-international.org). Pyloric atresia manifests with gastric abnormalities, primarily pyloric and duodenal atresia. However, in K5-Cre KO mice, the movement of coagulated milk from the pylorus into the intestine was not obstructed and consequently, the stomachs were not distended, ruling out that conditional knockout animals were suffering from pyloric atresia. Moreover, the absence of gastric pathologies in K5-Cre KO mice proved the targeting of the plectin gene to be exclusive for stratified epithelia, without affecting simple epithelia.
Even though the epidermis of OHT-treated Plecflox/–:K5-Cre-ERT mice showed only a mosaic pattern of plectin deletion, its susceptibility towards mechanical stress-induced damage was found to be clearly increased. Evidently, the patchwise deletion of plectin rendered the epidermis more prone to trauma, as revealed by increased TEWL and lesion formation. The observed more readily removable cells of the deeper epidermal cell layers by tape stripping may also be related to the lesion formation, although reduced cohesion of keratinocytes in the outer epidermal layers due to weakened desmosomal connections cannot be ruled out at the present stage.
Although we used quite high concentrations of OHT to activate Cre recombinase, plectin deletion was achieved only in patches of adult mouse epidermis. Inducible deletion of floxed genes in adult mice via Cre-ERT recombinase is not always 100% effective and appears to be especially difficult to achieve when cytoskeleton-associated proteins with a long half-life are targeted (López-Rovira et al., 2005). The very low turn-over rate of plectin in polarized epithelia (Eger et al., 1997) might explain the relatively weak deletion of plectin expression 14 days after Cre activation, since Cre is activated within 24 hours of the final OHT treatment (Indra et al., 1999). It might be advantageous for future studies to use K14-Cre-ERT2 mice, in which induction efficiency is more potent than in K5-Cre-ERT mice (Indra et al., 1999), and to combine this approach with topical application of OHT, which is less toxic than intraperitoneal injection (Vasioukhin et al., 1999) and can be done over longer periods (Benitah et al., 2005). Once more efficient deletion of plectin in adult stratified epithelia has been achieved, it will be interesting to re-evaluate skin barrier function, and moreover, investigate other yet unaddressed skin-related topics, such as wound healing and hair growth.
In summary, the generation of conditional stratified epithelia-specific plectin knockout mice has improved our understanding of the phenotypic manifestations of plectin deficiency in multilayered epithelia. Most importantly, the generation of mice carrying floxed plectin alleles makes it now possible to analyze the function of plectin in various other tissues known to be affected by EB-MD, such as skeletal muscle and brain. In addition, by refining the inducible knockout of plectin in skin, deeper insights into plectin functions in the adult organism might be gained, and a test system for the development of therapeutic approaches for skin-blistering in EB-MD/EB-PA might be obtained.
|
Materials and Methods |
|---|
|
TopSummaryIntroductionResultsDiscussionMaterials and MethodsReferences |
|---|
Engineering of plectin conditional knockout mice
To prepare the targeting construct, an FRT-PGKneor-FRT sequence plus a loxP site were inserted into intron 25 of the C-terminal part of the plectin gene. A second loxP site was introduced into intron 31. The targeting construct (linearized with SalI) was electroporated into E14.1 embryonic stem cells. Colonies resistant to geneticin (G418) were screened for the desired homologous recombination by Southern blotting. To generate chimeric mice, two recombinant ES cell clones (10-15 cells) harboring the conditional allele of the plectin gene (Plecflox(neo)) were injected into blastocysts (isolated from C57BL/6 mice at day 3.5 postcoitum; p.c.) that were transferred into pseudopregnant C57BL/6 x CBA females (3.5 day p.c.). A chimeric male offspring was then mated with C57BL/6 mice. Agouti coat-colored offspring was screened for the presence of the Plecflox(neo) allele by PCR analysis of tail DNA, using the primers Neo3086 (5'-TCGGCAGGAGCAAGGTGAGATG-3'), pleIn25-26U (5'-GTATTTGGATTCAGAGGCACAGTA-3') and pleEx26L (5'-CTTCAAGCTCTTGGAGAGTGGCAGG-3'), specific for neor, intron 25 and exon 26, respectively. Heterozygous mice were bred to FLP deleter mice and offspring was screened for the excised neor gene using primers pleIn25-26U and pleEx26L. After intercrossing mice that were heterozygous for the floxed Plec allele (Plec+/flox), homozygous mice were used to generate animals (Plec/:K5-Cre) that were transgenic for the K5-Cre recombinase and carried the deletion alleles of the plectin gene. The K5-Cre transgene was detected by PCR amplification with the primers Cre sense (5'-CCAATTTACTGACCGTACACC-3') and Cre antisense (5'-TAATCGCCATCTTCCAGCAGG-3'). The removal of exon 26 to exon 31 by Cre-mediated recombination was confirmed by Southern blotting and PCR analysis using primers pleIn25-26U and pleEx32/L7714 (5'-GCAGCCGCTGGTTTTCCTCCGCCA-3').
Preparation of 4-hydroxy-tamoxifen solutions
A 10 mg/ml 4-hydroxy-tamoxifen (OHT; Sigma) solution was prepared as described previously (Metzger and Chambon, 2001). Mice were injected with 1 mg OHT per day for 5 consecutive days.
Antibodies
For a complete list of primary antibodies refer to Table S1 in supplementary material. All secondary antibodies were purchased from Jackson Immuno-Research Laboratories (West Grove, PA).
Immunofluorescence and phase contrast microscopy of tissue sections, apoptosis assay, and dye penetration assay
Tissues were fixed in 4% paraformaldehyde in PBS and embedded in paraffin, or shock frozen in isopentane (cooled with liquid N2), sectioned (2 µm) on a cryomicrotome, and fixed in acetone at –20°C (Spazierer et al., 2006). Samples were examined using a Zeiss fluorescence laser-scanning microscope (LSM 510) or a Zeiss Axiophot microscope equipped with an AxioCam Hrc camera (Zeiss). Digital images were processed using Adobe Photoshop and Adobe Illustrator software.
Apoptosis was analyzed using the DeadEndTM Fluorimetric TUNEL System (Promega, Madison, WI). Dye penetration assays were performed as described previously (Spazierer et al., 2006).
Preparation of cell and tissue extracts, and immunoblotting
Epidermis and dermis from newborn mice were separated by treatment with dispase (30 minutes, 37°C), frozen in liquid nitrogen and pulverized. Tissue homogenates were prepared in Triton X-100 high-salt buffer (Eger et al., 1997) by mechanical disruption using a Polytron PT-3000 homogenizer (Kinematica, Littau-Luzern, Switzerland). Cell fractions were obtained from ground frozen tissue following the protocol of Vasioukhin et al. (Vasioukhin et al., 2001). Proteins were subjected to SDS-PAGE and immunoblotting as previously described (Spazierer et al., 2006).
Tape stripping, protein removal assay and TEWL
Tape stripping and measurement of transepidermal water loss (TEWL) were performed as described previously (Spazierer et al., 2006). TEWL of 1-day-old mice was measured with a Tewameter TM-300 equipped with a small-diameter (3 mm) probe, and measurements were digitally recorded via a MPA5 mulitprobe adapter (Courage and Khazaka, Cologne, Germany). The amount of protein removed per D-Squame disk (CuDerm corporation, Dallas, TX) was measured by a modification of the method of Dreher et al. (Dreher et al., 1998). Disks from two subsequent strippings were combined and the NaOH-soluble protein content after neutralization with HCl was determined using the Bio-Rad Protein Assay Kit. Absorption was measured with a spectrophotometer at 595 nm. An empty D-Squame disk and distilled water incubated with the Bio-Rad dye, served as negative controls. The amount of protein measured was then normalized to skin surface area (µg/cm2).
|
Acknowledgments |
|---|
|
Footnotes |
|---|
* These authors contributed equally to this work 
|
References |
|---|
|
TopSummaryIntroductionResultsDiscussionMaterials and MethodsReferences |
|---|
Abrahamsberg, C., Fuchs, P., Osmanagic-Myers, S., Fischer, I., Propst, F., Elbe-Bürger, A. and Wiche, G. (2005). Targeted ablation of plectin isoform 1 uncovers role of cytolinker proteins in leukocyte recruitment. Proc. Natl. Acad. Sci. USA 102, 18449-18454.
Andrä, K., Lassmann, H., Bittner, R., Shorny, S., Fässler, R., Propst, F. and Wiche, G. (1997). Targeted inactivation of plectin reveals essential function in maintaining the integrity of skin, muscle, and heart cytoarchitecture. Genes Dev. 11, 3143-3156.
Andrä, K., Nikolic, B., Stöcher, M., Drenckhahn, D. and Wiche, G. (1998). Not just scaffolding: plectin regulates actin dynamics in cultured cells. Genes Dev. 12, 3442-3451.
Andrä, K., Kornacker, I., Jörgl, A., Zörer, M., Spazierer, D., Fuchs, P., Fischer, I. and Wiche, G. (2003). Plectin-isoform-specific rescue of hemidesmosomal defects in plectin (–/–) keratinocytes. J. Invest. Dermatol. 120, 189-197.[CrossRef][Medline]
Benitah, S. A., Frye, M., Glogauer, M. and Watt, F. M. (2005). Stem cell depletion through epidermal deletion of Rac1. Science 309, 933-935.
Byrne, C. and Fuchs, E. (1993). Probing keratinocyte and differentiation specificity of the human K5 promoter in vitro and in transgenic mice. Mol. Cell. Biol. 13, 3176-3190.
Charlesworth, A., Gagnoux-Palacios, L., Bonduelle, M., Ortonne, J. P., De Raeve, L. and Meneguzzi, G. (2003). Identification of a lethal form of epidermolysis bullosa simplex associated with a homozygous genetic mutation in plectin. J. Invest. Dermatol. 121, 1344-1348.[CrossRef][Medline]
Chidgey, M., Brakebusch, C., Gustafsson, E., Cruchley, A., Hail, C., Kirk, S., Merritt, A., North, A., Tselepis, C., Hewitt, J. et al. (2001). Mice lacking desmocollin 1 show epidermal fragility accompanied by barrier defects and abnormal differentiation. J. Cell Biol. 155, 821-832.
Coulombe, P. A., Tong, X., Mazzalupo, S., Wang, Z. and Wong, P. (2004). Great promises yet to be fulfilled: defining keratin intermediate filament function in vivo. Eur. J. Cell Biol. 83, 735-746.[CrossRef][Medline]
DiPersio, C. M., van der Neut, R., Georges-Labouesse, E., Kreidberg, J. A., Sonnenberg, A. and Hynes, R. O. (2000). Alpha3beta1 and alpha6beta4 integrin receptors for laminin-5 are not essential for epidermal morphogenesis and homeostasis during skin development. J. Cell Sci. 113, 3051-3062.[Abstract]
Dowling, J., Yu, Q. C. and Fuchs, E. (1996). Beta4 integrin is required for hemidesmosome formation, cell adhesion and cell survival. J. Cell Biol. 134, 559-572.
Dreher, F., Arens, A., Hostynek, J. J., Mudumba, S., Ademola, J. and Maibach, H. I. (1998). Colorimetric method for quantifying human stratum corneum removed by adhesive-tape stripping. Acta Derm. Venereol. 78, 186-189.[CrossRef][Medline]
Eger, A., Stockinger, A., Wiche, G. and Foisner, R. (1997). Polarisation-dependent association of plectin with desmoplakin and the lateral submembrane skeleton in MDCK cells. J. Cell Sci. 110, 1307-1316.[Abstract]
Feil, R., Brocard, J., Mascrez, B., LeMeur, M., Metzger, D. and Chambon, P. (1996). Ligand-activated site-specific recombination in mice. Proc. Natl. Acad. Sci. USA 93, 10887-10890.
Green, K. J. and Gaudry, C. A. (2000). Are desmosomes more than tethers for intermediate filaments? Nat. Rev. Mol. Cell Biol. 1, 208-216.[CrossRef][Medline]
Guo, L., Degenstein, L., Dowling, J., Yu, Q. C., Wollmann, R., Perman, B. and Fuchs, E. (1995). Gene targeting of BPAG1: abnormalities in mechanical strength and cell migration in stratified epithelia and neurologic degeneration. Cell 81, 233-243.[CrossRef][Medline]
Indra, A. K., Warot, X., Brocard, J., Bornert, J. M., Xiao, J. H., Chambon, P. and Metzger, D. (1999). Temporally-controlled site-specific mutagenesis in the basal layer of the epidermis: comparison of the recombinase activity of the tamoxifen-inducible Cre-ER(T) and Cre-ER(T2) recombinases. Nucleic Acids Res. 27, 4324-4327.
Koch, P. J., Mahoney, M. G., Ishikawa, H., Pulkkinen, L., Uitto, J., Shultz, L., Murphy, G. F., Whitaker-Menezes, D. and Stanley, J. R. (1997). Targeted disruption of the pemphigus vulgaris antigen (desmoglein 3) gene in mice causes loss of keratinocyte cell adhesion with a phenotype similar to pemphigus vulgaris. J. Cell Biol. 137, 1091-1102.
Kunz, M., Rouan, F., Pulkkinen, L., Hamm, H., Jeschke, R., Bruckner-Tuderman, L., Brocker, E. B., Wiche, G., Uitto, J. and Zillikens, D. (2000). Mutation reports: epidermolysis bullosa simplex associated with severe mucous membrane involvement and novel mutations in the plectin gene. J. Invest. Dermatol. 114, 376-380.[CrossRef][Medline]
Liu, C. G., Maercker, C., Castanon, M. J., Hauptmann, R. and Wiche, G. (1996). Human plectin: organization of the gene, sequence analysis, and chromosome localization (8q24). Proc. Natl. Acad. Sci. USA 93, 4278-4283.
López-Rovira, T., Silva-Vargas, V. and Watt, F. M. (2005). Different consequences of beta1 integrin deletion in neonatal and adult mouse epidermis reveal a context-dependent role of integrins in regulating proliferation, differentiation, and intercellular communication. J. Invest. Dermatol. 125, 1215-1227.[CrossRef][Medline]
Mahrle, G., Schulze, H. J., Kuhn, A. and Wevers, A. (1989). Immunostaining of keratin and vimentin in epidermis: comparison of different post-embedding immunogold techniques for electron microscopy. J. Histochem. Cytochem. 37, 863-868.[Abstract]
Metzger, D. and Chambon, P. (2001). Site- and time-specific gene targeting in the mouse. Methods 24, 71-80.[CrossRef][Medline]
Peters, B., Kirfel, J., Bussow, H., Vidal, M. and Magin, T. M. (2001). Complete cytolysis and neonatal lethality in keratin 5 knockout mice reveal its fundamental role in skin integrity and in epidermolysis bullosa simplex. Mol. Biol. Cell 12, 1775-1789.
Pfendner, E. and Uitto, J. (2005). Plectin gene mutations can cause epidermolysis bullosa with pyloric atresia. J. Invest. Dermatol. 124, 111-115.[CrossRef][Medline]
Pfendner, E., Rouan, F. and Uitto, J. (2005). Progress in epidermolysis bullosa: the phenotypic spectrum of plectin mutations. Exp. Dermatol. 214, 241-249.
Raymond, K., Kreft, M., Janssen, H., Calafat, J. and Sonnenberg, A. (2005). Keratinocytes display normal proliferation, survival and differentiation in conditional beta4-integrin knockout mice. J. Cell Sci. 118, 1045-1060.
Rezniczek, G. A., de Pereda, J. M., Reipert, S. and Wiche, G. (1998). Linking integrin alpha6beta4-based cell adhesion to the intermediate filament cytoskeleton: direct interaction between the beta4 subunit and plectin at multiple molecular sites. J. Cell Biol. 141, 209-225.
Schara, U., Tucke, J., Mortier, W., Nüsslein, T., Rouan, F., Pfendner, E., Zillikens, D., Bruckner-Tuderman, L., Uitto, J., Wiche, G. et al. (2004). Severe mucous membrane involvement in epidermolysis bullosa simplex with muscular dystrophy due to a novel plectin gene mutation. Eur. J. Pediatr. 163, 218-222.[CrossRef][Medline]
Schoch, K. G., Lori, A., Burns, K. A., Eldred, T., Olsen, J. C. and Randell, S. H. (2004). A subset of mouse tracheal epithelial basal cells generates large colonies in vitro. Am. J. Physiol. Lung Cell. Mol. Physiol. 286, 631-642.
Spazierer, D., Fuchs, P., Reipert, S., Fischer, I., Schmuth, M., Lassmann, H. and Wiche, G. (2006). Epiplakin is dispensable for skin barrier function and for integrity of keratin network cytoarchitecture in simple and stratified epithelia. Mol. Cell. Biol. 26, 559-568.
Swensson, O., Langbein, L., McMillan, J. R., Stevens, H. P., Leigh, I. M., McLean, W. H., Lane, E. B. and Eady, R. A. (1998). Specialized keratin expression pattern in human ridged skin as an adaptation to high physical stress. Br. J. Dermatol. 139, 767-775.[CrossRef][Medline]
Tarutani, M., Itami, S., Okabe, M., Ikawa, M., Tezuka, T., Yoshikawa, K., Kinoshita, T. and Takeda, J. (1997). Tissue-specific knockout of the mouse Pig-a gene reveals important roles for GPI-anchored proteins in skin development. Proc. Natl. Acad. Sci. USA 94, 7400-7405.
Vasioukhin, V., Degenstein, L., Wise, B. and Fuchs, E. (1999). The magical touch: genome targeting in epidermal stem cells induced by tamoxifen application to mouse skin. Proc. Natl. Acad. Sci. USA 96, 8551-8556.
Vasioukhin, V., Bowers, E., Bauer, C., Degenstein, L. and Fuchs, E. (2001). Desmoplakin is essential in epidermal sheet formation. Nat. Cell Biol. 3, 1076-1085.[CrossRef][Medline]
Wiche, G. (1998). Role of plectin in cytoskeleton organization and dynamics. J. Cell Sci. 111, 2477-2486.[Abstract]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
|
|
 |
|
  J. Kostan, M. Gregor, G. Walko, and G. Wiche Plectin Isoform-dependent Regulation of Keratin-Integrin {alpha}6{beta}4 Anchorage via Ca2+/Calmodulin J. Biol. Chem., July 3, 2009; 284(27): 18525 - 18536. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Na, F. Chowdhury, B. Tay, M. Ouyang, M. Gregor, Y. Wang, G. Wiche, and N. Wang Plectin contributes to mechanical properties of living cells Am J Physiol Cell Physiol, April 1, 2009; 296(4): C868 - C877. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Konieczny, P. Fuchs, S. Reipert, W. S. Kunz, A. Zeold, I. Fischer, D. Paulin, R. Schroder, and G. Wiche Myofiber integrity depends on desmin network targeting to Z-disks and costameres via distinct plectin isoforms J. Cell Biol., October 17, 2008; 181(4): 667 - 681. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
