Cleavage-like cell division and explosive increase in cell number of neonatal gonocytes.
Based on previous conventional quantitative observations of rat testes, it was proposed that large numbers of gonocytes degenerate after birth and this notion was widely accepted. However, many studies show that neonatal gonocytes display high levels of mitotic activity. In order to resolve the apparent contradiction of increased mitotic activity in gonocytes despite a decrease in their numbers at the neonate stage, quantitative analysis using a marker of suitably higher resolution is required. It has been shown that the vasa protein could be used as a marker of germ cells. In this study, quantitative changes in gonocytes were re-examined using a germ-cell-specific marker in order to delineate more clearly the process of development from gonocytes to spermatogonia after birth. The vasa-positive cells, which correspond to gonocytes and spermatogonia, increased exponentially after birth. This observation suggests that all gonocyte divide actively after birth and do not degenerate as previously believed. Surprisingly, the cell volume of gonocytes decreased during their division. The largest population size was 2000-4000 micro3 at day 2, 1000-2000 micro3 at day 4 and 500-1000 micro3 at day 6. This finding suggests that gonocytes divide in a similar way to cleavage, which can be considered a special mode of fertilized eggs. Judging from the growth of seminiferous tubules and the degree of volume reduction, 60% of the contribution rate is estimated to be due to ordinal cell growth, and 40% due to volume reduction as in cleavage of a fertilized egg. This unique cleavage-like division may contribute to the supply of large numbers of spermatogonia.
Department of Anatomy, Kitasato University School of Medicine, Sagamihara 228-8555, Japan. ysakai@m.med.kitasato-u.ac.jp
Yasuhiro
Y
Sakai
Toshiaki
T
Noce
Shohei
S
Yamashina
D000818:Animals; D015415:Biomarkers; D002455:Cell Division / Q000502:physiology*; D007150:Immunohistochemistry; D008297:Male; D051379:Mice / Q000254:growth & development*; D012670:Seminiferous Epithelium / Q000166:cytology* / Q000254:growth & development*; D013091:Spermatogenesis / Q000502:physiology*
D015415:Biomarkers