Germ and somatic cell lineages in the developing gonad

The germ cell lineage in the mouse becomes lineage-restricted about 7.2 day s post coitum. Its progenitors have migrated from the proximal region of th e epiblast, where they were subject to a predisposing signal from the adjac ent extra-embryonic ectoderm. It appears that this and other signals determ ine the emergence of germ cells: unlike in some other organisms, this event is not pre-determined, After about 24 h in their initial extraembryonic lo cation, the primordial germ cells migrate back into the embryo and make the ir way into the legion of the developing gonad. Less is known about the ori gin of the various somatic cell lineages in the gonad, but some are known t o derive from cells that migrate in from the mesonephros and others from th e coelomic epithelium. Within the developing gonad, numerous interactions o ccur between the germ and somatic cell lineages. These are particularly imp ortant for the establishment of the spermatogenic lineage in the testis and for the differentiation of somatic tissue in the ovary. This payer will de scribe first the development of the germ cell lineage, up until about the t ime of birth, then the various somatic components of the gonad and finally the interactions that are known to occur between lineages. Unless otherwise stated, all the information refers to the mouse. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.