Autophagy and apoptosis interplay during follicular atresia in fish ovary: a morphological and immunocytochemical study

Abstract

Follicular atresia in fish ovary provides an interesting model for studying autophagy and apoptosis. In order to improve knowledge of the mechanisms regulating ovarian regression, we investigated the immunolocalisation of various proteins involved in the complex network of autophagy and apoptosis. Females of three species of freshwater fish maintained in captivity were sampled after the reproductive period and the main events of follicular atresia were assessed by histology: splits in the zona radiata, yolk degradation and reabsorption, hypertrophy of the follicular cells, accumulation of autophagic vacuoles, closing of the follicular lumen and thickening of the theca. The interplay of apoptosis and autophagy was analysed by TUNEL in situ and by immunocytochemistry for caspase-3, bax, bcl-2, beclin-1 and cathepsin-D. During early and advanced stages of follicular regression, the actin cytoskeleton was well developed and labelling for bcl-2 and cathepsin-D were pronounced in the follicular cells at a stage when they were intensively involved in yolk phagocytosis. Immunofluorescence for beclin-1 was prevalent in the follicular cells, punctate labelling often surrounding autophagic vacuoles during the advanced stage of follicular regression, a critical step towards cell death. TUNEL-positive reaction and immunostaining for bax and caspase-3 demonstrated the participation of apoptosis in late follicular regression. Overall, this study provides evidence that autophagic and apoptotic proteins are activated in a coordinated fashion depending on the stage of follicular regression, with interplay between autophagy and apoptosis being essential in determining the fate of the cell during follicular atresia in fish ovary.

High insulin impaired ovarian function in early pregnant mice and the role of autophagy in this process

“…ment, and protein homeostasis. Autophagy is reported to contribute to the maintenance of ovarian functioning in many ways [23][24][25]. Insulin is reported to be involved in the regulation of autophagy, and studies have shown that insulin can inhibit autophagy through activating mTORC1 (mechanistic target of rapamycin complex 1) and PKB (protein kinase B) [26].…”

Alterations in gene expression during fasting-induced atresia of early secondary ovarian follicles of coho salmon, Oncorhynchus kisutch

“…Although no genes involved in autophagy were found in the present SSH libraries, some recent studies have indicated that both autophagic and apoptotic processes are involved in follicular atresia in fishes (Morais et al, 2012;Gioacchini et al, 2013). Autophagy is a catabolic pathway for the recycling of cytoplasmic components (Kang et al, 2011).…”

“…Autophagy is a catabolic pathway for the recycling of cytoplasmic components (Kang et al, 2011). In Characiformes, the autophagic protein, beclin-1, associated with the accumulation of autophagic vacuoles has a central role in autophagy, concomitantly acting with apoptotic proteins such as bax and caspase 3 during follicular atresia in hypertrophied follicular cells, suggesting that both autophagy and apoptosis are activated in a coordinated fashion (Morais et al, 2012). Thus, analysis of some candidate genes involved in autophagy may be worthwhile to obtain additional gene markers of atresia.…”

Hatching enzymes disrupt aberrant gonadal degeneration by the autophagy/apoptosis cell fate decision

“…Gonadal atresia, a nutrient-circulating process, is activated in a synchronized manner and involves both autophagy and apoptosis 7, 35 . Starvation and high temperature (HT) are known to induce atresia in various animals 36 .…”

“…Two pathways of PCD, apoptosis and autophagy, have been well characterized in several species 7 . While apoptosis and autophagy may occur together or distinctly, the expected outcome is the physiological removal of marked cells, leading to the development of new structures (morphogenesis), removal of damaged cells, and tissue homeostasis.…”