A study on division of primordial germ cells in the early chick embryo

Abstract

The purpose was to determine the sites, times and frequency of mitotic activity in primordial germ cells in the white Leghorn chick embryo during the period of migration. Colchicine was employed to facilitate the identification of dividing germ cells in embryos ranging in age from 18 hours to five days of incubation (stages 3-27). An increase in the number of germ cells was observed during the period of migration, due primarily to proliferation of intraembryonic cells, since no significant increase in the number of extra-embryonic germ cells was seen during this period. The number of germ cells during this period ranged from 43 at 18 hours to 2211 at 120 hours. Two periods of intense proliferation were observed, the first between 48 and 72, the second between 96 and 120 hours. This coincided with a simultaneous increase in the number of germ cells during these periods. Dividing germ cells were present in the extraembryonic blood vessels anterior, lateral and posterior to the embryo at 28, 48 and 72 hours and within the intra-embryonic circulatory network at 48, 72, 96 and 120 hours. At 72, 96 and 120 hours, dividing germ cells were numerous in the tissues of the dorsal mesentery adjacent to the developing gonads and within the gonads. Dividing germ cells were also located in head mesenchyme, limb buds and mesenchyme surrounding the notochord-neural tube complex. Dividing germ cells were found in the chick embryo throughout the entire migratory period.

Left-Right Asymmetry in Chicken Embryonic Gonads

“…It is not yet clear what actually controls asymmetric germ cell distribution. It is possible that chemotactic and/or mitogenic factors play a role in germ cells migration, and it has been proposed that the left gonadal ridge secretes such factors more than the right, leading to increased PGCs migration and/or division in the left gonad (Witschi, 1935;Swartz and Domm, 1972). One study supported this by showing that engrafted quail PGCs differentially colonized the left and right presumptive gonads at limb bud stages (HH 18-24) (Didier and Fargeix, 1976).…”

Extragonadal distribution of primordial germ cells in the early chick embryo

“…Ectopic PGCs may gradually and slightly increase in number by their own cell division. In regard to this, Swartz and Domm (1972) observed dividing PGCs in extragonadal sites in the chick, and also reported that in the figure). G, future gonadal area.…”

“…After leaving the blood vessels, the PGCs finally migrate into the developing gonadal anlagen in the embryo proper (Swift, 1914;Fujimoto et al, 1976). However, it has been reported that, in the chick embryo, some PGCs deviate from the normal route of their migration and are found in extragonadal sites (Swartz and Domm, 1972). In lower vertebrates, a similar abnormal localization of PGCs has been noted; 25% of the germ cells are ectopic in elasmobranchs (Beard, 1902) and 5% in urodeles (Humphrey, 1925).…”

Genistein causes germ cell reduction in the genital ridges of Japanese quail Coturnix japonica embryo

“…We found that the number of quail PGCs was reduced significantly by two doses of genistein. It has been reported that mitotic figures can be found in dividing PGCs during germ cell migration (Swartz and Domm 1972). Thus, genistein may inhibit germ cell division and proliferation.…”