Graduate Student University of Southern Mississippi HATTIESBURG, Mississippi, United States
Abstract Authors: Godspower N. Okeke1, 2, Janice P. Evans3, Nicole (Nikki) J. Camlin1, 2 1. Cell and Molecular Biology, School of Biological, Environmental and Earth Sciences, University of Southern Mississippi, Hattiesburg, MS 2. Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, MS 3. Department of Biological Sciences, Purdue University, West Lafayette, IN
Abstract Text: Acquisition of meiotic competence by oocytes is critical for meiotic resumption and for successful embryo development. Previous research has found the phosphatase PP1 becomes enriched in the nucleus during acquisition of meiotic competence. However, the mechanisms regulating this are unclear. Proper meiotic events, such as nuclear envelope breakdown, rely on the precise activation or inhibition of PP1. Importantly, PP1 is a holoenzyme consisting of a catalytic subunit and one of over 200 regulatory subunits. NIPP1 (nuclear inhibitor of protein phosphatase 1) is a on such regulator that inhibits PP1. We hypothesized that NIPP1 plays a role in oocyte meiotic competence via PP1 regulation. In this study, we investigated the relationship between NIPP1 localization and the acquisition of meiotic competence, classifying oocytes based on DNA morphology into meiotically incompetent (non-surrounded nucleolus; NSN) and meiotically competent (surrounded nucleolus; SN). Using immunofluorescence, we observed a distinct NIPP1 localization pattern between NSN and SN. We observed three localization patterns: enriched in the nucleus, excluded from the nucleus, and even distribution between the cytoplasm and the nucleus. In meiotically incompetent oocytes (NSN), NIPP1 was predominantly nuclear enriched (p < 0.0001). Conversely, NIPP1 in meiotically competent oocytes (SN) was evenly distributed (p = 0.0045). In support of this nuclear-to-cytoplasmic shift, the nuclear-to-cytoplasmic ratio of NIPP1 was significantly lower in SN oocytes compared to NSN oocytes (p < 0.0001). This reflects a transition of NIPP1 from the nucleus to the cytoplasm as oocytes acquire meiotic competence. These findings indicate that the localization of NIPP1 is dynamically regulated during meiotic competence acquisition. The reduction of nuclear NIPP1 in SN oocytes is potentially linked to decreased nuclear PP1 inhibition. This increased PP1 activity could play a role in meiotic resumption. Future studies will elucidate the role of NIPP1 in oocyte maturation via NIPP1 knockdown experiments. By carefully observing how this affects the timing of nuclear envelope breakdown, the formation of the meiotic spindle, and other critical steps in meiosis, we will define the NIPP1 role in oocyte maturation.
