Nanos is required to prevent mitosis and somatic differentiation and for the pole cells to migrate to function as PGCs (see next section).
In addition to these genes, Pgc polar granule component blocks phosphorylation and consequently activation of RNA polymerase II and shuts down transcription.
[citation needed] Similar germ plasm has been identified in Amphibians in the polar cytoplasm at the vegetal pole.
In frogs, the PGCs migrate along the mesentery to the gonadal mesoderm facilitated by orientated extracellular matrix with fibronectin.
[citation needed] In birds, the PGCs arise from the epiblast and migrate to anteriorly of the primitive streak to the germinal crest.
[3] In the mouse, primordial germ cells (PGCs) arise in the posterior primitive streak of the embryo[4] and start to migrate around 6.25 days after conception.
PGCs start to migrate to the embryonic endoderm and then to the hindgut and finally towards the future genital ridges where the somatic gonadal precursors reside.
[4] Around 10 days post conception; the PGCs occupy the genital ridge[5] where they begin to lose their motility and polarized shape.
[6] In mice, PGCs originate from the proximal epiblast, close to the extra-embryonic ectoderm (ExE), of the post-implantation embryo as early as embryonic day 6.5.
[8][9][10] The epiblast, however, also give rise to somatic cell lineages that make up the embryo proper; including the endoderm, ectoderm and mesoderm.
[22] WNT3 mutants fail to establish a primordial germ cell population, but this can be restored with exogenous WNT activity.
[14] In this way, Blimp1 and Prdm14 drive PGC specification by promoting germ line development and potential pluripotency transcriptional programs while also keeping the cells from taking on a somatic fate.
[14] With the vast knowledge about in-vivo PGC specification collected over the last few decades, several attempts to generate in-vitro PGCs from post-implantation epiblast were made.
[34] PGC-like cells generated using this method can be transplanted into a gonad, where the differentiate, and are able to give viable gametes and offspring in vivo.
Point mutations or deletions in the human or mouse Sry coding region can lead to female development in XY individuals.
In the gonads, the germ cells undergo either spermatogenesis or oogenesis depending on whether the sex is male or female respectively.
[citation needed] Mitotic germ stem cells, spermatogonia, divide by mitosis to produce spermatocytes committed to meiosis.
[46] In Drosophila, the ability of premeiotic male germ line cells to repair double-strand breaks declines dramatically with age.
[48] Mitotic germ stem cells, oogonia, divide by mitosis to produce primary oocytes committed to meiosis.
After puberty in primates, small groups of oocytes and follicles prepare for ovulation by advancing to metaphase II.
Meiosis is asymmetric producing polar bodies and oocytes with large amounts of material for embryonic development.