REPRESSION OF GENE-EXPRESSION IN THE EMBRYONIC GERM LINEAGE OF C-ELEGANS

THE distinction between soma and germline was recognized more than a c entury ago: somatic cells form the body of an organism, whereas germ c ells serve to produce future generations', In Caenorhabditis elegans, the separation of soma and germline occurs through a series of asymmet rical divisions, in which embryonic germline blastomeres divide unequa lly to produce one somatic daughter and one germline daughter(2), Here we show that after each asymmetrical division, embryonically transcri bed RNAs are detected in somatic, but not germline, blastomeres, This asymmetry depends on the activity of the germline-specific factor, PIE -1, In the absence of PIE-1, embryonically transcribed RNAs are detect ed in both somatic and germline blastomeres, Furthermore, ectopic expr ession of PIE-1 in somatic blastomeres can significantly reduce the ac cumulation of new transcripts in these cells, Taken together, these re sults suggest that germ-cell fate depends on an inhibitory mechanism t hat blocks new gene expression in the early embryonic germ lineage.