LIN-5 is a novel component of the spindle apparatus required for chromosome segregation and cleavage plane specification in Caenorhabditis elegans

Successful divisions of eukaryotic cells require accurate and coordinated c ycles of DNA replication, spindle formation, chromosome segregation, and cy toplasmic cleavage. The Caenorhabditis elegans gene lin-5 is essential for multiple aspects of cell division. Cells in lin-5 null mutants enter mitosi s at the normal time and form bipolar spindles, but fail chromosome alignme nt at the metaphase plate, sister chromatid separation, and cytokinesis. De spite these defects, cells exit from mitosis without delay and progress thr ough subsequent rounds of DNA replication, centrosome duplication, and abor tive mitoses, In addition, early embryos that lack lin-5 function show defe cts in spindle positioning and cleavage plane specification. The lin-5 gene en-codes a novel protein with a central coiled-coil domain. This protein l ocalizes to the spindle apparatus in a cell cycle- and microtubule-dependen t manner. The LIN-5 protein is located at the centrosomes throughout mitosi s, at the kinetochore microtubules in metaphase cells, and at the spindle d uring meiosis. Our results show that LIN-5 is a novel component of the spin dle apparatus required for chromosome and spindle movements, cytoplasmic cl eavage, and correct alternation of the S and RI phases of the cell cycle.