2002 West Coast Worm Meeting abstract 61
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HHMI and MCD Biology, University of Colorado, Boulder, CO, 80309
Little is know about organelle membrane proteins that mediate the anchorage of nuclei and organelles within cells. We show here that ANC-1 functions to position syncytial nuclei and muscle mitochondria by linking the actin cytoskeleton to the nuclear envelope. Mutations in anc-1 disrupt the proper positioning of nuclei and mitochondria in Caenorhabditis elegans. anc-1 was shown to encode an 8546 residue protein consisting of mostly coiled regions and a C-terminal nuclear envelope localization domain (KASH domain) conserved with the Drosophila klarsicht and msp-300 and vertebrate syne-1 and syne-2 genes. The N-terminal regions of ANC-1, Msp-300, Syne-1, and Syne-2 contain two calponin-like domains; the ANC-1 domain bound to filamentous actin in vitro. When overexpessed, the N-terminal region of ANC-1 co-localized with actin filaments, disrupted muscle function, and partially disrupted nuclear anchorage. An actin disrupting mutation in unc-60/cofilin also disrupted mitochondrial anchorage. Antibodies against the large repeat region of ANC-1 were localized cytoplasmically, and were enriched at the nuclear periphery. Localization of ANC-1 to the nuclear envelope was dependent on UNC-84, another nuclear envelope-localized protein required for nuclear anchorage. Overexpression of the KASH domain localized to the nuclear envelope and caused a dominant negative nuclear anchorage defect. We propose that ANC-1 connects nuclei to the cytoskeleton by interacting with UNC-84 at the nuclear envelope and directly binding to actin in the cytoplasm. Similarity in the overall structure between ANC-1, Msp-300, and vertebrate Syne proteins suggests that this novel nuclear anchorage mechanism is conserved. Potential similarities between the mechanisms of ANC-1 and Dystrophin will be discussed.