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Development of primordial germ cells in the mouse *
Author(s) -
McLaren A.
Publication year - 2009
Publication title -
andrologia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.633
H-Index - 59
eISSN - 1439-0272
pISSN - 0303-4569
DOI - 10.1111/j.1439-0272.1992.tb02647.x
Subject(s) - epiblast , biology , gastrulation , germ line development , mesoderm , primitive streak , endoderm , microbiology and biotechnology , germ cell , embryonic stem cell , yolk sac , somite , germ layer , stem cell , embryo , embryogenesis , anatomy , genetics , gene , induced pluripotent stem cell
Summary. Primordial germ cells in the mouse are known to be derived from the epiblast. They can be identified histochemically, by their high alkaline phosphatase activity. At 8 d post coitum they have been observed within the embryonic part of the egg cylinder, at the posterior end of the primitive streak. Earlier, at 7.25 days post coitum , we have observed them embedded in the extra‐embryonic mesoderm, as a tight clump. Germ cell counts over the 7–8 d period of gastrulation have been made. They are consistent with either of two models: (1) derivation of the germ cell lineage from a very small stem cell pool, followed by a constant rate of proliferation, and (2) derivation from a larger initial stem cell pool, followed by a period when germ cells are differentiating but not dividing. From their initial extra‐embryonic location, germ cells spread into the mesoderm of the primitive streak, and the endoderm of the yolk sac and hind gut. Active locomotion is probably required for their passage up the dorsal mesentery and into the genital ridges. Mutant alleles at two loci, W (White‐spotting) and Sl (Steel), drastically reduce the number of germ cells reaching the ridges. Since those that succeed in reaching the ridges suffer little if any delay, the defect is unlikely to be due to reduced powers of locomotion, but rather to a failure of proliferation or survival. W acts cell‐autonomously: its gene product is the c‐kit polypeptide, a transmembrane tyrosine kinase receptor. Sl acts through the tissue environment, and has been shown to encode a peptide growth factor variously termed SCF (stem cell factor) or MGF (mast cell growth factor). SCF is presumed to act as a ligand for the c‐kit receptor molecule, in a signal transduction pathway functioning not only in primordial germ cells, but also in the other two cell types affected by W and Sl , namely haemopoietic stem cells and melanoblasts. A few days after colonizing the genital ridges, germ cells (XX or XY) in an ovary enter meiosis, but in a testis they undergo mitotic arrest and do not enter meiosis until a week after birth, as primary spermatocytes. The inhibitory effect is exerted by some diffusible substance emanating from the somatic tissue of the testis: germ cells at a sufficient distance from the testis are able to enter meiosis and develop as oocytes. Thus the phenotypic sex of a germ cell (oocyte or spermatocyte) is determined by its tissue environment, not by its own chromosome constitution.