SEGREGATION OF GERM GRANULES IN LIVING CAENORHABDITIS-ELEGANS EMBRYOS- CELL-TYPE-SPECIFIC MECHANISMS FOR CYTOPLASMIC LOCALIZATION

Germ granules are ribonucleoprotein particles that are thought to func tion in germline specification in invertebrates and possibly in verteb rates. In Caenorhabditis elegans, these structures, termed P granules, are partitioned to the germline P cells during the early embryonic di visions, By injecting a fluorescently labelled anti-P-granule antibody into the C. elegans germline syncitium, we followed P-granule segrega tion in live embryos using laser-scanning confocal microscopy. We show that, in early P cells (P-0 and P-1), P-granule partitioning is achie ved primarily by their migration through the cytoplasm towards the sit e of formation of the germline daughter cell. A different mechanism ap pears to operate in later P cells (P-2 and P-3): P granules associate with the nucleus and move with it toward the site of formation of the germline daughter cell, where they are then deposited, At each divisio n, there is also disassembly or degradation of those P granules that r emain in the cytoplasm destined for the somatic daughter cell, Microfi laments, microtubules and the product of the gene mes-1 are required f or the normal pattern of P-granule segregation in P-2.