Transcript level of NF-kappa-B inhibitor alpha (IkBa) is regulated during mammalian meiosis.

NF-kB is a transcription factor involved in the regulation of gamete maturation, a complex process, which concludes meiosis. This process that sustains genome reprogramming and embryo development is associated to a specific expression pattern. NF-kB activity is primarily regulated by interaction with inhibitory proteins (IkB). The best-studied NF-kB-IkB interaction is IkBa-p50/RelA that inhibits the NF-kB activity by masking its NLS domain and so blocking the ability of NF-kB to bind DNA. NF-kB-IkBa complex is continuously shuttling between the nucleus and the cytoplasm, but its nuclear export rate exceeds its import rate and thus the complex is generally cytoplasmic. An upregulation of IkBa expression has been observed in association with murine oocyte aging suggesting that a deregulation of NF-kB pathway may be related to oocyte competence. However, NF-kB signalling studies during oocyte maturation have been limited. In male gamete development, NF-kB is activated in a stage-specific manner. It appears at pachitene and remains activated in the following germinal differentiation steps triggering specialized genes expression. We report on the study of IkBa in bovine oocytes at different meiotic stages that are transcriptionally quiescent: diplotene of prophase I and metaphase II. During this time, a subset of maternal transcript undergoes post-transcriptional regulation and is stored protected; when the protein is required, dormant transcripts can undergo polyadenylation and translation, and rapid degradation. Immature oocytes arrested in diplotene were obtained from bovine cumulus ovary and in vitro meiosis progression were performed with FSH and estradiol hormones. Using Real-TimePCR, we examined IkBa transcript levels in immature and mature oocyte pools. We included four expressed oocyte genes that are BMP15, GDF9, SPIN1, FMR1. We examined also ZAR1, as a specific oocyte maturation marker, whose transcript generally underwent degradation during meiosis. Our data showed a reduction of IkBa transcript during in vitro nuclear maturation suggesting that oocyte competence could be regulated through NF-kB pathway. Western-blot analysis in immature and mature oocytes is currently carrying out to correlate transcript and protein levels. Further analysis will be performed to establish how IkBa is regulated during developmental competence and if it is involved in human diseases such as premature aging and infertility.