from Section 2 - Life cycle
Published online by Cambridge University Press: 05 October 2013
Introduction
Mammalian ovarian formation and differentiation takes place early in life, often before birth, but the ovary is not ready to fulfill its main purpose, that is, to ovulate a mature oocyte, until puberty. During early fetal development the germ cells populate the gonadal areas in close association with the mesonephros. The following developmental pattern of the ovary differs greatly among species, but one parameter is a must for all: each germ cell differentiates to an oocyte and becomes together with granulosa cells enclosed in a follicular entity. The pool of follicles is final and determines the length of the future reproductive lifespan. The finely tuned interaction between germ cells and somatic cells early in life is therefore crucial.
Origin and migration of primordial germ cells (PGCs) from the epiblast to the gonadal anlage: role of the autonomic nervous system
The classic concept of gonadal formation is that the PGCs arise in the proximal part of the yolk sac, the proximal epiblast [1], and migrate a relatively long distance within the hindgut that grows towards the area where the gonads will develop, around somite 16 [2]. Then the PGCs leave the hindgut and move towards the developing gonads at the ventral part of the mesonephros. Thus, the PGCs are first guided by the hindgut and thereafter by other mechanisms to the gonadal anlage. The importance of the hindgut for PGC movement was shown in Sox17-null mouse embryos in which the hindgut does not expand and the PGCs become immobilized in the hindgut [3].
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