α-endosulfine (ENSA) regulates exit from prophase I arrest in mouse oocytes

Abstract

Mammalian oocytes in ovarian follicles are arrested in meiosis at prophase I. This arrest is maintained until ovulation, upon which the oocyte exits from this arrest, progresses through meiosis I and to metaphase of meiosis II. The progression from prophase I to metaphase II, known as meiotic maturation, is mediated by signals that coordinate these transitions in the life of the oocyte. ENSA (α-endosulfine) and ARPP19 (cAMP-regulated phosphoprotein-19) have emerged as regulators of M-phase, with function in inhibition of protein phosphatase 2A (PP2A) activity. Inhibition of PP2A maintains the phosphorylated state of CDK1 substrates, thus allowing progression into and/or maintenance of an M-phase state. We show here ENSA in mouse oocytes plays a key role in the progression from prophase I arrest into M-phase of meiosis I. The majority of ENSA-deficient oocytes fail to exit from prophase I arrest. This function of ENSA in oocytes is dependent on PP2A, and specifically on the regulatory subunit PPP2R2D (also known as B55δ). Treatment of ENSA-deficient oocytes with Okadaic acid to inhibit PP2A rescues the defect in meiotic progression, with Okadaic acid-treated, ENSA-deficient oocytes being able to exit from prophase I arrest. Similarly, oocytes deficient in both ENSA and PPP2R2D are able to exit from prophase I arrest to an extent similar to wild-type oocytes. These data are evidence of a role for ENSA in regulating meiotic maturation in mammalian oocytes, and also have potential relevance to human oocyte biology, as mouse and human have genes encoding both Arpp19 and Ensa.

Greatwall kinase at a glance

“…Conversely, although Arpp19 and ENSA appear to be essential for proper meiotic progression in this case, most data converge to suggest that the principal function of these substrates is in metaphase I progression. Accordingly, ENSA knockdown in mouse oocytes and the absence of Ensa in Drosophila mutant oocytes prevents prophase I exit (Von Stetina et al, 2008;Matthews and Evans, 2014), whereas, once phosphorylated by Gwl, Arpp19 promotes entry into meiotic divisions (Dupre et al, 2013). Arpp19 is additionally phosphorylated on S109 by the protein kinase A (PKA) during prophase I in Xenopus oocytes.…”

Selective dephosphorylation by PP2A-B55 directs the meiosis I - meiosis II transition in oocytes

“…These results point to PP2A-B55 as a critical conductor of cell cycle progression in oocytes. In diverse species, ARPP19/ENSA is required for exit from Prophase I arrest by inhibiting PP2A-B55 (Dupre et al, 2013;Dupré et al, 2014;Matthews and Evans, 2014;Okumura et al, 2014;Von Stetina et al, 2008). Our data in the sea star indicate that phosphatase activity is critical not only for maintaining the Prophase I arrest, but also to drive the transition between the two meiotic divisions.…”

Mitogenic Signals Stimulate the CREB Coactivator CRTC3 through PP2A Recruitment

“…Various cellular proteins can inhibit PP2A activity, including the phosphorylation-dependent regulators of mitosis ENSA, ARPP19, and Bod1 (Gharbi-Ayachi et al., 2010, Porter et al., 2013). In contrast to CRTC3 (Song et al., 2010), these proteins are small (12–20 kDa) (The UniProt Consortium, 2017) and knockdown or overexpression of any one regulator typically leads to growth arrest and embryonic lethality (Dupre et al., 2014, Matthews and Evans, 2014). Arguing against a role for CRTC3 as a PP2A inhibitor, cellular PP2A activity and proliferation appeared comparable between cells expressing WT or phosphorylation-defective (S391A) CRTC3 in HEK 293T cells (Figure S5).…”