Abandonment of germ cells in the embryonic chick ovary: TEM and SEM studies.

Abstract

Embryonic chick ovary forms medulla and cortex successively in early developmental stages. Unlike the cortex, which is a functioning tissue in the adult, the medulla regresses as development advances. Although germ cells are included in these respective regions, their behavior within these regions is different. This study focuses on the fate of germ cells in the medulla of both ovaries. Germ cells found in the medulla of the developing chick ovary from 7 to 19 days of incubation were observed by TEM and SEM. From 10 days of incubation onward, medullary germ cells in both right and left ovaries were often released into medullary lacunae. During the releasing process, germ cells were covered by thin cytoplasm of epithelial cells of the lacunae. After release, however, they were freed from the thin coat of epithelial cells. Abandoned germ cells were seen in the lacunae as solitary cells or as a mass composed of several cells. In the right ovary, germ cells released into the lacunae were subsequently found at the holes of the ovarian surface, which were continuous with the medullary lacunae. Moreover, germ cell death was often found in late stages in the medullary tissues of both right and left ovaries. The present study clarifies the fact that chick germ cells of the medulla of both right and left ovaries are either discarded by a process of programmed cell death and/or released into medullary lacunae with increasing embryo age.