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doi: 10.1242/10.1242/jcs.00248

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ANChors away: an actin based mechanism of nuclear positioning

Howard Hughes Medical Institute and Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA

View larger version (12K): [in a new window]   Fig. 1. UNC-84 and ANC-1 are conserved. On the left, the family of SUN domain-containing proteins is depicted. The SUN domains (tan) are between 34 and 47% identical to the UNC-84 SUN domain. All of these proteins, except the Drosophila member (which might not be full length) have a predicted trans-membrane domain (pink). On the right, the Syne/ANC-1 proteins are depicted. The last 60 residues are the KASH domain (light blue) with a predicted trans-membrane domain (pink). These domains are between 50 and 60% identical to one another. The N-termini of these proteins contain two calponin-like domains of about 100 residues each (red). The large central region (blue) of ANC-1 consists of mostly novel repetitive stretches, while central regions of the others consist of mostly spectrin repeats. These domains are both predicted to form extended rod-like structures.

View larger version (27K): [in a new window]   Fig. 2. A model for nuclear anchorage and migration is shown. The KASH domain (light blue) is targeted to the outer nuclear membrane (ONM) through an interaction with the SUN domain (tan) of UNC-84 (yellow), which may occur through an intermediating protein or complex (gray circle). This predicts that Syne/ANC-1, UNC-84, the nuclear lamina, and other unknown proteins create a bridge across both nuclear membranes. Such a novel mechanism would require that the outer nuclear membrane be independently specified from the endoplasmic reticulum (ER) or nuclear pores (gray). The calponin domains of Syne (red) attach to actin microfilaments (green) to effectively anchor nuclei in the cytoplasm.

View larger version (15K): [in a new window]   Fig. 3. Is there a potential role for Syne/ANC-1 in Muscular Dystrophy? This model points out the similarities between the mechanisms of Syne/ANC-1 and dystrophin. Both of these huge proteins bind to actin through N-terminal calponin domains, and extend spectrin repeats through the cytoplasm. Both then function as part of a bridge across membranes. Mutations in many of these components lead to muscular dystrophy (see text).