Morphological patterns of cell death in ovarian follicles of primary and secondary growth and postovulatory follicle complex of the annual killifish Millerichthys robustus (Cyprinodontiformes: Cynolebiidae).

The dynamics of cellular development and homeostasis of the ovary depend on the balance between proliferation and cell death throughout the reproductive cycle. Millerichthys robustus is an annual fish whose ovarian follicles develop asynchronously, allowing daily reproduction from sexual maturity until death. The objective of this research is to describe, histologically, the processes of follicular atresia and regression of postovulatory follicular complexes (POC) throughout a reproductive cycle of M. robustus. Patterns of cell death were documented by apoptosis in atretic follicles and POC, and necrosis in the POC after ovulation with an associated inflammatory response. Atretic follicles were seen from the onset of sexual maturity, during week three post-hatching (PH), both in primary growth (from the Cortical alveoli step, with folliculogenesis completed) and secondary growth Stages, with a higher prevalence in the latter. POCs were observed in different stages of regression from week four PH until the death of the fish. The apoptotic characteristics found were: (i) fragmentation of the nuclear membrane and zona pellucida, and liquefaction of the cortical alveoli and yolk; (ii) follicular cells becoming phagocytic, increasing their size, and migrating within the oocyte; and (iii) formation of an intrafollicular lumen, a product of phagocytosis of the oocyte constituents and dispersed pigments that remain after the digestion of yolk and cortical alveoli. The morphological changes of the follicular cells of the POC, from a squamous morphology after ovulation to columnar during its regression with PAS+ contents, was documented, suggesting a secretory activity.

Ovarian structure, folliculogenesis and oogenesis of the annual killifish Millerichthys robustus (Cyprinodontiformes: Cynolebiidae).

Cellular aspects of oocyte development of the Mexican rivulus Millerichthys robustus were morphologically described in order to analyze ovarian function and the cellular recruitment dynamics associating it with life history strategies of annual killifishes. Millerichthys is an iteroparous batch spawner with continuous oocyte recruitment and indeterminate fecundity with asynchronous development of the follicles. It has two ovaries of cystovarian type, with a central lumen, which communicates with the outside through the caudal region of the ovary, that is, the gonoduct. From the walls of the ovary, irregular lamellae composed of germinal epithelium and vascularized stroma project. Oogenesis starts with oogonial proliferation, found alone or in nests within the germinal epithelium. The oogonia come into meiosis becoming oocytes and advancing to the chromatin nucleolus stage and to early primary growth stage. Folliculogenesis is completed in the primary growth stage and cortical alveoli step. Follicles moves toward the stroma, but they continue to be attached to the germinal epithelium through the basement membrane until ovulation. The inclusion of fluid yolk in the follicles during the secondary growth stage was observed. During ovulation, the follicle collapsed, the oocyte was released into the lumen, and the constitutive elements of the post-ovulatory follicle complex remained in the stroma.

Relationship between bcl-2, bax, beclin-1, and cathepsin-D proteins during postovulatory follicular regression in fish ovary.

In fish ovaries, postovulatory follicles (POFs) are key biomarkers of breeding and provide an interesting model for studying the relationship between autophagy and apoptosis. In this study, we investigated the immunohistochemical expression of autophagic and apoptotic proteins to improve the knowledge on the mechanisms regulating ovarian remodeling after spawning. Females from three neotropical fish species kept in captivity were submitted to hormonal induction. After ova stripping, ovarian sections were sampled daily until 5 days postspawning (dps). Similar events of POF regression were detected by histology, terminal transferase-mediated dUTP nick-end labeling (TUNEL), and electron microscopy in the three species: follicular cells hypertrophy, progressive disintegration of the basement membrane, gradual closing of the follicular lumen, theca thickening, and formation of large autophagic vacuoles preceding apoptosis of the follicular cells. Autophagic and apoptotic proteins were assessed by immunohistochemistry. Morphometric analysis of the immunolabeling revealed a more intense reaction for bcl-2 and beclin-1 (BECN1) in POFs at 0 to 1 dps and for bax at 2 to 3 dps (P < 0.001), the later period being the peak of apoptosis of the follicular cells. The immunostaining for cathepsin-D was more elevated until 2 to 3 dps and decreased significantly at 4 to 5 dps, when the POFs were in late stage of regression. Double labeling for BECN1 and caspase-3 indicated a shift in the relationship between autophagy and apoptosis at 2 to 3 dps, a critical period in determining the fate of follicular cells in POFs. Together, these results indicate that the bcl-2 family, BECN1, and cathepsin-D can be involved in the regulation of ovarian remodeling in teleost fish.

Evidence of a role for prolactin as regulators of ovarian follicular development in goose

Background Prolactin (PRL) regulates development and reproduction, and its effects are mediated by the prolactin receptor (PRLR). In order to clarify the role of PRLR and PRL in the process of follicular development in the goose ovary, the level of PRLR mRNA expression in the ovary and follicles of the Sichuan white goose was determined, as well as the PRL concentration in ovarian follicles. Results The level of PRLR mRNA in the hierarchical follicles (HFs) initially increased, and subsequently decreased, whereas PRLR expression was initially low and later increased in postovulatory follicles (POFs). The level of PRLR mRNA expression was the highest in the F4 follicles, and lowest in the F1 follicles in all of the examined follicles. Compared with the level of PRLR mRNA expression in the small white follicles (SWFs), the level of PRLR mRNA was 2.86- and 1.44-fold higher in the F4 and small yellow follicles (SYFs), respectively (P < 0.05). The level of PRLR mRNA expression in the F4 follicles was highest (P < 0.05) in HFs. The highest PRL concentration in all of the examined samples was observed in SYFs and F1, with concentration of 6162 mLU/g and 6197 mLU/g, respectively. The PRL concentration in SYFs was significantly higher compared with SWFs (P < 0.05). Conclusions The change of PRL concentration was similar to the PRLR mRNA expression level in preovulatory follicles. These results suggest that the PRL mediated by the PRLR plays a stimulatory role in the SWF to SYF transition.