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

Abstract

The ovaries of early embryos (40 days after fertilization) of the bat Carollia perspicillata contain numerous germ-line cysts, which are composed of 10 to 12 sister germ cells (cystocytes). The variability in the number of cystocytes within the cyst and between the cysts (that defies the Giardina rule) indicates that the mitotic divisions of the cystoblast are asynchronous in this bat species. The 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 the later stages of embryonic development (44–46 days after fertilization), the somatic cells penetrate the cyst, and their cytoplasmic projections separate individual oocytes. Separated oocytes surrounded by the 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 non-canonical) in the fetal ovaries of C. perspicillata indicate that the formation of germ-line cysts is an evolutionarily conserved phase in the development of the female gametes throughout the animal kingdom.

Histological description of gonadal development in a neotropical insectivorous bat Eumops patagonicus (Chiroptera: Molossidae)

“…Moreover, in the undifferentiated gonad that becomes in the ovary, the primitive sex cord formed for the rst time and secondly the epithelium continuously proliferation and forms de second generation of sex cords (Lamothe et al, 2020). This aligns with the initiation of gonadal differentiation at the 17 developmental stage, as described for S. lilium (Porras-Gomez et al, 2017) Studies in C. perspicillata (Lechowska et al, 2012) describe early oogenesis in prenatal ovaries, noting the presence of germ line PGCs forming germ cell cysts by the 12th developmental stage. In E. patagonicus, cysts are observed in an advanced stage of development, speci cally at stage 23.…”

“…However, data pertaining to gonadogenesis within this order remain largely absent. Recently, early oogenesis has been delineated in Carollia perspicillata (Lechowska et al, 2012), where the formation of germ cell cysts consisting of 10 to 12 germ cells (oogonia) was observed in embryonic ovaries. Furthermore, the presence of transient cytoplasmic bridges between distinct cysts, an unusual feature, was noted.…”

Female mice lack adult germ-line stem cells but sustain oogenesis using stable primordial follicles

“…Female germ-line biology provides clear predictions of how individual lineage-labeled germ cells will behave, depending on whether the primordial follicle pool is maintained by stem cells. During mouse fetal germ-line development (16,17) and in known cases in which adult female GSCs maintain vertebrate oocyte production (18,19), progenitor cell progeny do not differentiate directly into oocytes, but first undergo a series of special mitotic divisions with incomplete cytokinesis to form germ-line cysts (20,21). We lineagemarked widely spaced, random germ cells within the adult ovary and followed the behavior of individual cells and their progeny over time (Fig.…”

Ovarian nests in cultured Russian sturgeon Acipenser gueldenstaedtii and North American paddlefish Polyodon spathula comprised of previtellogenic oocytes

“…Cells that were interconnected by this bridge most probably represented PE 1 or EP 1 according to the classification presented in this study. In vertebrates, the bridges that lack a rim were described in the ovaries of embryos obtained from Seba's short‐tailed fruit bats Carollia perspicillata (Lechowska et al , ).…”