AUTHOR=Konar Essaikiammal Sodalai Muthu , Mai Knut , Brachs Sebastian , Waghmare Swapnil Gorakh , Samarin Azadeh Mohagheghi , Policar Tomas , Samarin Azin Mohagheghi 

TITLE=Evaluation of viability, developmental competence, and apoptosis-related transcripts during in vivo post-ovulatory oocyte aging in zebrafish Danio rerio (Hamilton, 1822)

JOURNAL=Frontiers in Veterinary Science

VOLUME=11

YEAR=2024

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1389070

DOI=10.3389/fvets.2024.1389070

ISSN=2297-1769

ABSTRACT=<sec><title>Introduction</title><p>Post-ovulatory aging is a time-dependent deterioration of ovulated oocytes and a major limiting factor reducing the fitness of offspring. This process may lead to the activation of cell death pathways like apoptosis in oocytes.</p></sec><sec><title>Methodology</title><p>We evaluated oocyte membrane integrity, egg developmental competency, and mRNA abundance of apoptosis-related genes by RT-qPCR. Oocytes from zebrafish <italic>Danio rerio</italic> were retained <italic>in vivo</italic> at 28.5°C for 24 h post-ovulation (HPO). Viability was assessed using trypan blue (TB) staining. The consequences of in vivo oocyte aging on the developmental competence of progeny were determined by the embryo survival at 24 h post fertilization, hatching, and larval malformation rates.</p></sec><sec><title>Results</title><p>The fertilization, oocyte viability, and hatching rates were 91, 97, and 65% at 0 HPO and dropped to 62, 90, and 22% at 4 HPO, respectively. The fertilizing ability was reduced to 2% at 8 HPO, while 72% of oocytes had still intact plasma membranes. Among the apoptotic genes <italic>bcl-2</italic> (b-cell lymphoma 2), <italic>bada</italic> (bcl2-associated agonist of cell death a), <italic>cathepsin D, cathepsin Z, caspase 6a, caspase 7, caspase 8, caspase 9, apaf1, tp53</italic> (tumor protein p53), <italic>cdk1</italic> (cyclin-dependent kinase 1) studied, mRNA abundance of anti-apoptotic <italic>bcl-2</italic> decreased and pro-apoptotic <italic>cathepsin D</italic> increased at 24 HPO. Furthermore, <italic>tp53</italic> and <italic>cdk1</italic> mRNA transcripts decreased at 24 HPO compared to 0 HPO.</p></sec><sec><title>Discussion</title><p>Thus, TB staining did not detect the loss of oocyte competency if caused by aging. TB staining, however, could be used as a simple and rapid method to evaluate the quality of zebrafish oocytes before fertilization. Taken together, our results indicate the activation of cell death pathways in the advanced stages of oocyte aging in zebrafish.</p></sec>