Global decay of mRNA is a hallmark of apoptosis in aging Xenopus eggs

2021

Antioxidants

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Aging of oocytes and eggs diminishes their reproductive and developmental potential. It has been demonstrated previously that reactive oxygen species (ROS) contribute to accelerated aging of various cells. In the present study, we measured intracellular levels of ROS and investigated effects of several selective antioxidants (AOXs) on the viability and functional activity of aging oocytes and eggs of the African clawed frog Xenopus laevis. The fluorescent cell-permeable dye DCFDA, which is widely employed for ROS detection in cultured mammalian cells, was used to monitor ROS levels in the fresh and bench-aged oocytes and eggs by an optimized protocol. It was found that intracellular ROS contents were increased in frog oocytes and eggs aged for 48 h. It was further demonstrated using selective cell-permeable AOXs targeting different ROS-generating mechanisms, that the major source of ROS in Xenopus oocytes and eggs is the plasma membrane NADPH oxidase, and that mitochondrial generation contributes to the intracellular ROS content to a lesser extent. Targeted inhibition of NADPH oxidase with a natural organic compound apocynin reduced ROS levels significantly in Xenopus oocytes and eggs, maintained their normal phenotype and supported their functional competence. To our knowledge this is the first report concerning beneficial effects of apocynin on the isolated gamete cells, such as oocytes and eggs.

Section: Discussionsupporting

confidence: 93%

Modulation of Intracellular ROS and Senescence-Associated Phenotypes of Xenopus Oocytes and Eggs by Selective Antioxidants

2021

Antioxidants

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“…61 Our more recent studies demonstrated that numerous cytoplasmic mRNAs are robustly degraded in apoptotic Xenopus eggs. 62 63 Apoptotic events were also observed in cell-free extracts of Xenopus eggs, 64 propagating through the egg cytoplasm as apoptosis trigger waves. 65 Notably, only interphase extracts, but not extracts arrested in metaphase, are susceptible to apoptosis.…”

Section: S P Ontaneous Oo C Y Te De Athmentioning

confidence: 94%

“…It has been demonstrated that extracellular signal (eg, sperm)‐independent exit from metaphase II arrest, which we term “spontaneous activation,” precedes apoptosis . Our more recent studies demonstrated that numerous cytoplasmic mRNAs are robustly degraded in apoptotic Xenopus eggs . Such global decay of mRNA is mediated by endonucleolysis and becomes evident in the eggs after meiotic exit at the time of cytochrome c release.…”

Section: Spontaneous Oocyte Deathmentioning

confidence: 95%

Toward the understanding of biology of oocyte life cycle in Xenopus Laevis: No oocytes left behind

Reprod Medicine & Biology

2020

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Background For the past more than 25 years, we have been focusing on the developmental and reproductive biology of the female gametes, oocytes, and eggs, of the African clawed frog Xenopus laevis. Methods The events associated with the life cycle of these cells can be classified into the four main categories: first, oogenesis and cell growth in the ovary during the first meiotic arrest; second, maturation and ovulation that occur simultaneously and result in the acquisition of fertilization competence and the second meiotic arrest; third, fertilization, that is sperm‐induced transition from egg to zygote; and fourth, egg death after spontaneous activation in the absence of fertilizing sperm. Main findings Our studies have demonstrated that signal transduction system involving tyrosine kinase Src and other oocyte/egg membrane‐associated molecules such as uroplakin III and some other cytoplasmic proteins such as mitogen‐activated protein kinase (MAPK) play important roles for successful ovulation, maturation, fertilization, and initiation of embryonic development. Conclusion We summarize recent advances in understanding cellular and molecular mechanisms underlying life cycle events of the oocytes and eggs. Our further intention is to discuss and predict potentially promising impact of the recent findings on the challenges facing reproductive biology and medicine, as well as societal contexts.

“…It has been reported previously that unfertilized matured Xenopus oocytes die by a well-defined apoptotic process within 48–72 h of hormonal stimulation ( Du Pasquier et al, 2011 ; Tokmakov et al, 2011 ; Iguchi et al, 2013 ). Eggs from different species, including mammals, have been shown to die by apoptosis in the absence of fertilization ( Tokmakov et al, 2017 , 2018 ). Clearance of large follicle-entrapped apoptotic eggs from the ovaries may represent a formidable homeostatic challenge that would potentially overload the immune system.…”

Section: On the Coordination Of Maturation And Follicular Rupturementioning

confidence: 99%

Dissection of the Ovulatory Process Using ex vivo Approaches

Стефанов

2020

Front. Cell Dev. Biol.

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Ovulation is a unique physiological phenomenon that is essential for sexual reproduction. It refers to the entire process of ovarian follicle responses to hormonal stimulation resulting in the release of mature fertilization-competent oocytes from the follicles and ovaries. Remarkably, ovulation in different species can be reproduced out-of-body with high fidelity. Moreover, most of the molecular mechanisms and signaling pathways engaged in this process have been delineated using in vitro ovulation models. Here, we provide an overview of the major molecular and cytological events of ovulation observed in frogs, primarily in the African clawed frog Xenopus laevis, using mainly ex vivo approaches, with the focus on meiotic oocyte maturation and follicle rupture. For the purpose of comparison and generalization, we also refer extensively to ovulation in other biological species, most notoriously, in mammals.