Germ Cell Specification
The germline of Caenorhabditis elegans derives from a single founder cell, the germline blastomere P4. P4 is the product of four asymmetric cleavages that divide the zygote into distinct somatic and germline (P) lineages. P4 inherits a specialized cytoplasm (“germ plasm”) containing maternally encoded proteins and RNAs. The germ plasm has been hypothesized to specify germ cell fate, but the mechanisms involved remain unclear. Three processes stand out: (1) inhibition of mRNA transcription to prevent activation of somatic development, (2) translational regulation of the nanos homolog nos-2 and of other germ plasm mRNAs, and (3) establishment of a unique, partially repressive chromatin. Together, these processes ensure that the daughters of P4, the primordial germ cells Z2 and Z3, gastrulate inside the embryo, associate with the somatic gonad, initiate the germline transcriptional program, and proliferate during larval development to generate ∼2,000 germ cells by adulthood.
KeywordsGerm plasm Polarity Germ granules Cell fate Transcriptional repression Germline blastomeres Primordial germ cells P lineage Maternal RNA
We thank members of the Seydoux lab for helpful discussions. We gratefully acknowledge funding from NIH (T32 HD007276 to J.W. and HD037047 to G.S.) and the Howard Hughes Medical Institute.
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