Primordial germ cell-somatic cell partnership: A balancing cell signaling act

Recent studies demonstrate that the normal progression of the germ cell lin eage during gonadogenesis involves a delicate balance of primordial germ ce ll survival and death factors generated by surrounding somatic cells. This balance operates in a different fashion in females and males. The fine tuni ng primordial germ cell specification in the wall of the yolk sac, migratio n through the hindgut and dorsal mesentery, and colonization in the urogeni tal ridges involves the temporal and spatial activation of the following si gnaling pathways: Primordial germ cell specification involves bone morphoge netic proteins 2, 4 and 8b, and their migration is facilitated by the c-kit receptor-ligand duet. When colonization occurs: (1) neuregulin-beta ligand is expressed and binds to an ErbB2-ErbB3 receptor tyrosine kinase heterodi mer on primordial germ cells; (2) Vasa, an ortholog of the Drosophila gene vasa, member of an ATP-dependent RNA helicase of the DEAD (Asp-Glu-Ala-Asp) -box family protein is also expressed by primordial germ cells; (3) Bcl-x ( cell survival factor) and Bax (cell death factor) join forces to modulate t he first burst of primordial germ cell apoptosis; (4) Cadherins, integrins, and disintegrins bring together primordial germ cells and somatic cells to organize testis and ovary. Information on other inducers of primordial cel l survival, such as TER (teratoma) factor, is beginning to emerge. (C) 2001 Wiley-Liss, Inc.