MRT-2 checkpoint protein is required for germline immortality and telomerereplication in C-elegans

The germ line is an immortal cell lineage that is passed indefinitely from one generation to the next. To identify the genes that are required for ger mline immortality, we isolated Caenorhabditis elegans mutants with mortal g erm lines-worms that can reproduce for several healthy generations but even tually become sterile. One of these mortal germline (mrt) mutants, mrt-2, e xhibits progressive telomere shortening and accumulates end-to-end chromoso me fusions in later generations, indicating that the MRT-2 protein is requi red for telomere replication. In addition, the germ line of mrt-2 is hypers ensitive to X-rays and to transposon activity. Therefore, mrt-2 has defects in responding both to damaged DNA and to normal double-strand breaks prese nt at telomeres. mrt-2 encodes a homologue of a checkpoint gene that is req uired to sense DMA damage in yeast. These results indicate that telomeres m ay be identified as a type of DNA damage and then repaired by the telomere- replication enzyme telomerase.