Segregation of primordial germ cells: Their numbers and fate during early development of Barbus conchonius (Cyprinidae, Teleostei) as indicated by ³H‐thymidine incorporation

Abstract

H-Thymidine incorporation experiments in Barbus conchonius showed that presumptive primordial germ cells (PGCs) terminated their mitotic activity between midepibolys, and late epiboly. At the ten-somite stage, shortly after labeling of PGCs by uptake of H-thymidine became arrested, they could be recognized by their relatively large size and large nucleus. They were located in two longitudinal rows of cells between mesoderm and periblast, always at the same distance to the left and right of the notochord. Contact with the endoderm was not observed before the 16- to 23-somite stage. The numbers of PGCs were small (mean number, 18-19) and remained small for nearly 3 weeks. Mitotic activity was not observed in PGCs during that period; thereafter, rapid proliferation began. There is no evidence for active migration of PGCs; it is assumed that they are merely translocated passively together with their surrounding tissues. No specific constituents were detected with histochemical methods for glycogen, alkaline phosphatase, and RNA. Electron microscopy revealed the presence of "nuage" around the nucleus of PGCs. This material corresponded with perinuclear dense bodies as seen with light microscopy from the 19-somite stage onward. It is concluded that presumptive PGCs segregate from the somatic cells between midepiboly and late epiboly, before the three germ layers have been formed, and that locations of PGCs in the endodermal or mesodermal layer may be merely transitory stages during their translocation toward the gonadal primordia.

Germ Cell Lineage from a Single Blastomere at 8-Cell Stage in Shiro-uo (ice goby)

“…Serial sections were cut at a thickness of 8 µ m, and stained with hematoxylin-eosin, using standard procedures. PGCs were confirmed based on location and characteristics similar to those observed in other teleosts; round shape, relatively large size, large nuclei, and clear nuclear membrane (Hamaguchi, 1982;Timmermans and Taverne, 1989;Braat et al , 1999;Kazama-Wakabayashi et al ., 1999;Nagai et al ., 2001).…”

Germline Cysts and the Formation of the Germinal Epithelium During the Female Gonadal Morphogenesis in Cyprinus carpio (Teleostei: Ostariophysi: Cypriniformes)

“…The period between time zero and the 7th day post-fertilization, includes embryogenesis, and it is the period when the primordial germ cells migrate from extragonadal regions to the genital ridge giving arise to the gonadal primordium (Satoh, 1974;Hamaguchi, 1982;Timmermans and Taverne, 1989;Winkoop et al, 1992;Flores and Burns, 1993). The gonadal primordium, found along both sides of the swim bladder and dorsal to the gut, can be identified by the presence of large primordial germ cells surrounded by somatic cells that are coming from the genital ridge (Parmentier and Timmermans, 1985;Timmermans et al, 1996; current study).…”

Histological Differentiation of Primordial Germ Cells in Zebrafish

“…In these animals, germ line cells can be identified only after the expression of morphological features of germ cells. In teleost, PGCs have been investigated exclusively by both light and electron microscopy (Johnston, 1951;Gamo, 1961;Hamaguchi, 1982;Timmermans and Taverne, 1989;Gevers et al, 1992b;Kazama-Wakabayashi et al, 1999;Braat et al, 1999). In these studies, PGCs have been identified by their morphological characteristics, namely roundish shape, relatively large size, large nucleus, and a clear nuclear membrane.…”

“…In these studies, PGCs have been identified by their morphological characteristics, namely roundish shape, relatively large size, large nucleus, and a clear nuclear membrane. Eosinophilic granules have been reported as histological characteristics common to PGCs in some species, such as medaka (Gamo, 1961), rosy barb (Timmermans and Taverne, 1989), and goldfish (Kazama-Wakabayashi et al, 1999). However, fish PGCs have not been traced back by these histological markers to before the gastrula period.…”