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First published online 8 July 2008
doi: 10.1242/jcs.033233

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Progression of meiotic recombination requires structural maturation of the central element of the synaptonemal complex

¹ Department of Cell and Molecular Biology, Karolinska Institute, Berzelius väg 35, Stockholm, SE-171 77, Sweden
² Medical Research Council Human Genetics Unit, Western General Hospital, Edinburgh EH4 2XU, Scotland, UK
³ Department of Cell and Developmental Biology, Biocenter of the University of Würzburg, Am Hubland, Würzburg 97074, Germany

View larger version (19K): [in this window] [in a new window]   Fig. 1. Generation of Tex12–/– mice. (A) Exon 2 to exon 5 of the Tex12 gene were replaced by a neomycin cassette to generate Tex12–/– mice. (B,C) The mice were genotyped using PCR (black primers in A, two in the gene, one in the neomycin cassette) and did not contain the Tex12 RNA (RT-PCR, grey primers in A, positive control using Trip13) or protein (western blot, WB, positive control -tubulin).

View larger version (73K): [in this window] [in a new window]   Fig. 2. Histological analysis of wild-type and Tex12–/– testes and ovaries. (A) Spermatogenesis is halted at epithelial stage IV in the Tex12–/– testes leading to a total absence of round and elongated spermatids. Stages of the seminiferous epithelium are shown as roman numerals. Different testicular cell types depicted are: Int, intermediate spermatogonia; Ls, leptotene spermatocytes; Zs, zygotene spermatocytes; Ps, pachytene spermatocytes; Ps*, apoptotic spermatocytes; Ds, diplotene spermatocytes; M, meiotic cell division; Rs, round spermatids; Es, elongated spermatids; Ser, Sertoli cells. Oogenesis proceeds until the dictyate arrest stage, even though 30% of the oocytes are lost during early embryonic development. After birth, the Tex12–/– oocytes degenerate rapidly and virtually no oocytes can be found in ovaries more than 1 week after birth. Oocytes are labeled with anti-GCNA (brown). Bars: 20 µm (testes) and 5 µm (ovaries). (B) Average number of oocytes (± s.e.m.) per ovary in wild-type and Tex12–/– ovaries at embryonic stage E16.5 and day 1 after birth (n=3).

View larger version (49K): [in this window] [in a new window]   Fig. 3. Initiation of synapsis without an intact central element. Meiotic chromosomes in wild-type and Tex12–/– spermatocytes and oocytes immunolabeled for SYCP1 (transverse filaments, green), STAG3 (axial elements, blue) and SYCE1 (central elements, red) (A) or STAG3 (axial elements, green) and SYCE2 (central elements, red) (B). Centromeres are labeled with CREST (white) (B). Bar: 5 µm.

View larger version (121K): [in this window] [in a new window]   Fig. 4. Initiation of synapsis without an intact central element. Electron microscopy of the synaptonemal complex in wild-type, Tex12–/– and Sycp1–/– oocytes and spermatocytes. AE, axial elements (lateral elements after synapsis); TF, transverse filaments; CE, central element; CE*, central-element-like structure. Bar: 100 nm. A schematic representation of these results is shown in the cartoon at the bottom left.

View larger version (42K): [in this window] [in a new window]   Fig. 5. The central element is required for the development of meiotic crossovers. (A) Meiotic chromosomes in wild-type and Tex12–/– oocytes immunolabeled for STAG3 (axial elements, green) and DMC1 (red, E16.5 and E18.5), RPA (red, E17.5 and E18.5) or MLH1 (red, E18.5). Centromeres are labeled with CREST (white). Bar: 5 µm. (B) Average number of DMC1 and RPA foci (± s.e.m.) at E16.5 (wt, n=7; –/–, n=4) and E18.5 (wt, n=12; –/–, n=9) and E17.5 (wt, n=6; –/–, n=10) and E18.5 (wt, n=10; –/–, n=9).

View larger version (19K): [in this window] [in a new window]   Fig. 6. Repair of DNA double-strand breaks is impaired without an intact central element. Meiotic chromosomes in wild-type and Tex12–/– E17.5 oocytes immunolabeled for STAG3 (axial elements, green) and -H2AX (red) or BRCA1 (red). Centromeres are labeled with CREST (white). Bar: 5 µm.

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