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Becoming Haploid

Session: Poster Session C

(8) The Protein Phosphatase 1 regulatory protein NIPP1 is enriched around the meiotic spindle 

Friday, August 1, 2025
8:30 AM - 9:30 AM EDT
Location: Marquis Ballroom 6-10
Abstract Authors:

Elizabeth D Lawrence1, 2, Tolulope E Ademulegun1, 2, Janice P Evans3, and Nikki J Camlin1, 2. 





  1. Cell and Molecular Biology, School of Biological, Environmental and Earth Sciences, University of Southern Mississippi, Hattiesburg, MS 








  1. Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, MS 








  1. Department of Biological Sciences, Purdue University, West Lafayette, IN 





Abstract Text: Protein phosphatase 1 (PP1) plays an essential role in meiotic maturation in mammalian oocytes. Inhibition and activation of PP1 during mouse oocyte meiotic maturation leads to oocyte death and / or signification meiotic abnormalities. PP1 is a holoenzyme consisting of a catalytic subunit and one of over 200 regulatory subunits. Importantly, these regulatory subunits dictate PP1’s activity, localization, and substrates. NIPP1 (nuclear inhibitor of protein phosphatase 1) is one of the most widely studied PP1 regulators, and as its name suggests inhibits PP1’s catalytic activity. In the testis, gene-deletion of NIPP1 (murine model) impairs spermatogenesis via reduced proliferation and survival of germ cells. Furthermore, overexpression of NIPP1 in mitotic HeLa cells causes prometaphase arrest. Finally, NIPP1 is expressed in sea star oocytes, with sites essential for PP1-NIPP1 interaction phosphorylated during M-Phase re-entry (germinal vesicle breakdown). Of note, phosphorylation of these sites prevents PP1-NIPP1 interaction. However, if NIPP1 is expressed and plays a function role in mammalian oocytes unknown. This preliminary study set out to determine if NIPP1 was expressed in mouse oocytes and define its subcellular localization. We found NIPP1 at an mRNA and protein level in oocytes. NIPP1 localization at germinal vesicle stage was dynamic (discussed in detail in presentation by Godspower Okeke). After germinal vesicle breakdown (3 hours post-meiotic release) and at metaphase II arrest we observed NIPP1 throughout the cytoplasm but also enriched around the microtubules. Notably, this enrichment was not on the metaphase spindles, but rather round the periphery of the spindle. Future studies aim to fully characterize the localization of NIPP1 through murine oocyte meiosis, define the phospho-status of NIPP1 during oocyte maturation, and determine the impact of NIPP1 loss on meiotic progression.