Extragonadal distribution of primordial germ cells in the early chick embryo

Abstract

Chick primordial germ cells (PGCs), after separation from the endoderm in early embryonic development, temporarily circulate via the blood vascular system and finally migrate into the gonadal anlagen. It has been noted by some authors that some PGCs are present in extragonadal sites in some vertebrates. In the present study, we examined the distribution and localization of PGCs in extragonadal sites in the chick embryo. PGCs were identified by periodic acid-Schiff staining with light microscopy. In embryos at stages 20-24 (PGCs are in the settlement stage in the gonadal primordium), approximately 20% of the total number of PGCs were observed in extragonadal regions. Approximately 90% of these ectopic PGCs were found in the head, mainly in the mesenchyme surrounding the neural tube. Even at stage 14 when PGCs were usually circulating in the blood vessels, some of the PGCs had emerged from the blood vessels and were detected in the extragonadal site. This pattern of distribution of ectopic PGCs in the head area is probably attributed to the earlier, dominant development of the capillary network, and to the sluggish capillary blood flow in that region, which allows intravascular PGCs to escape into the tissue.

Is the embryo culture system useful for collecting primordial germ cells from endangered avian embryos?

“…In chickens, the optimal developmental stages for collection of PGCs were stages 14 and 15, in both the S.II-cultured embryos and the control intact embryos. Previous studies have shown that in intact chick embryos the highest number of PGCs circulate in the blood vessels during stages 13 and 15, and that the number of circulating PGCs varies with the developmental stage [Singh and Meyer, 1967;Nakamura et al, 1988;Tajima et al, 1999]. The present results using the S.II-cultured embryos showed, in accordance with those previous findings, that the number of PGCs circulating in the bloodstream (and recoverable) reached a peak at stage 14 and then decreased.…”

Migratory Ability of Chick Primordial Germ Cells Transferred into Quail Embryos

“…The present results are in agreement with those of Yasuda et al [7], who transferred 100 chick PGCs into the marginal sinus of 2.5-day-old quail embryos and found that approximately 63 and 13% of the PGCs were in the gonadal and extragonadal regions of the quail embryos 24 h after transfer, respectively. Nakamura et al [25] reported that the proportion of extragonadal PGCs in the normal developing 3-day-old chick embryo at stage 19 [6] is 15.5%. These results indicate that extragonadal migration of chick PGCs occurs probabilistically in normal Chick PGC located in the mesenchyme of the trunk (arrow).…”

A Novel Method to Isolate Primordial Germ Cells and Its Use for the Generation of Germline Chimeras in Chicken1

“…The chick PGCs migrate into the germinal ridge [1][2][3][4], where they differentiate into either spermatogonia in the testis or oogonia in the ovary. The unique migratory pathway of avian PGCs facilitates their isolation and transfer, especially from the blood vessels.…”