Early oogenesis in the short-tailed fruit bat Carollia perspicillata: transient germ cell cysts and noncanonical intercellular bridges

The ovaries of early embryos (40 days post coitum/p.c.) of the bat Carollia perspicillata contain numerous germ-line cysts, which are composed of 10 to 12 sister germ cells (cystocytes). Variability in the number of cystocytes within the cyst and between the cysts (defying the Giardina rule) indicates that the mitotic divisions of the cystoblast are asynchronous in this bat species. Serial section analysis showed that the cystocytes are interconnected via intercellular bridges that are atypical, strongly elongated, short-lived, and rich in microtubule bundles and microfilaments. During slightly later stages of embryonic development (44-46 days p.c.), somatic cells penetrate the cyst, and their cytoplasmic projections separate individual oocytes. Separated oocytes surrounded by a single layer of somatic cells constitute the primordial ovarian follicles. The oocytes of C. perspicillata are similar to mouse oocytes and are asymmetric. In both species, this asymmetry is clearly recognizable in the localization of the Golgi complexes. The presence of germ-line cysts and intercellular bridges (although noncanonical) in the fetal ovaries of C. perspicillata suggest that the formation of germ-line cysts is an evolutionarily conserved phase in the development of the female gametes in a substantial part of the animal kingdom.