Analyses of the regulatory mechanism of porcine WEE1B: the phosphorylation sites of porcine WEE1B and mouse WEE1B are different.
ABSTRACT WEE1B, an oocyte-specific kinase, phosphorylates the CDC2 inhibitory site and maintains the meiotic arrest of oocytes at the first meiotic prophase in several mammalian species. However, the molecular mechanisms controlling WEE1B activity have not been fully examined in species other than mice. In the present study, we analyzed the regulation mechanisms of porcine WEE1B (pWEE1B), focusing on the cAMP-dependent protein kinase (PKA) phosphorylation site and intracellular localization. As the PKA phosphorylation site in mouse WEE1B (mWEE1B) was not conserved in pWEE1B, we predicted that four serine residues would be phosphorylatable by PKA in pWEE1B (Ser77, Ser118, Ser133 and Ser149) and constructed FLAG-tagged replaced-pWEE1Bs, in which each of the PKA-phosphorylatable serines was mutated into a non-phosphorylatable alanine. We injected one of their mRNAs into porcine immature oocytes and found that the Ser77-replaced pWEE1B lost the WEE1B function, whereas the wild-type and other replaced-pWEE1Bs could maintain the meiotic arrest of oocytes. Next, the localization of pWEE1B was examined by immunohistochemistry, and exclusive nuclear localization was revealed in the fully grown oocytes. We generated a nuclear localization signal (NLS)-deleted pWEE1B (ΔNLS-pWEE1B) and then overexpressed it in porcine immature oocytes. We found that ΔNLS-pWEE1B was distributed uniformly in the cytoplasm and could not maintain the meiotic arrest of porcine oocytes. These results suggest that pWEE1B is activated after phosphorylation of the Ser77 residue, which is different from the phosphorylation site that activates mWEE1B; that pWEE1B is localized in the nucleus; and that the nuclear localization is essential for its function.
- [Show abstract] [Hide abstract]
ABSTRACT: Mammalian growing oocytes (GOs) lack the ability to resume meiosis, although the molecular mechanism of this limitation is not fully understood. In the present study, we cloned cDNAs of cAMP-dependent protein-kinase (PKA) subunits from porcine oocytes and analyzed the involvement of the PKA regulation mechanism in the meiotic incompetence of GOs at the molecular level. We found a cAMP-independent high PKA activity in GOs throughout the in vitro culture using a porcine PKA assay system we established, and inhibition of the activity by injection of the antisense RNA of the PKA catalytic subunit (PKA-C) induced meiotic resumption in GOs. Then we examined the possibility that the amount of the PKA regulatory subunit (PKA-R), which can bind and inhibit PKA-C, was insufficient to suppress PKA activity in GOs because of the overexpression of two PKA-Rs, PRKAR1A and PRKAR2A. We found that neither of them affected PKA activity and induced meiotic resumption in GO although PRKAR2A could inhibit PKA activity and induce meiosis in cAMP-treated full-grown oocytes (FGOs). Finally, we analyzed the subcellular localization of PKA subunits and found that all the subunits were localized in the cytoplasm during meiotic arrest and that PKA-C and PRKAR2A, but not PRKAR1A, entered into the nucleus just before meiotic resumption in FGOs, whereas all of them remained in the cytoplasm in GOs throughout the culture period. Our findings suggest that the continuous high PKA activity is a primary cause of the meiotic incompetence of porcine GOs and that this PKA activity is not simply caused by an insufficient expression level of PKA-R, but can be attributed to more complex spatial-temporal regulation mechanisms.Biology of Reproduction 06/2012; 87(3):53. · 3.45 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Most mammalian oocytes are arrested at the germinal vesicle stage by activation of Wee1B. Meiotic resumption is regulated by inactivation of Wee1B and activation of cell division cycle 25B. The aim of this study was to determine whether treatment with Wee1B-targeting small interfering RNA (Wee1B-siRNA) promotes nuclear maturation of canine oocytes from germinal vesicle stage to metaphase II (MII) stage. In experiment 1, the percentage of canine oocytes that matured to MII stage was higher (P < 0.05) among oocytes cultured in vitro for 72 hours than among those cultured for 24 and 48 hours (5.4 ± 2.5% vs. 0.0 ± 0.0% and 1.4 ± 1.0%, respectively). Furthermore, the percentage of oocytes that matured to metaphase I (MI) stage was higher (P < 0.05) among oocytes cultured for 48 and 72 hours than among those cultured for 24 hours (14.9 ± 10.0% and 22.4 ± 8.1%, respectively, vs. 5.7 ± 6.0%). In experiment 2, canine oocytes were intracytoplasmically microinjected with Wee1B-siRNA (50 μM) at various culture time points (0, 24, 48, or 72 hours). The nuclear configuration of the exception of oocytes in the 72-hour group was examined after 84 hours of culture. The percentage of oocytes that matured to the MII stage was higher (P < 0.05) among those treated with Wee1B-siRNA at 0 hours than among control oocytes and those injected at 72 hours (18.0 ± 1.7% vs. 2.1 ± 2.8% and 0.0 ± 0.0%, respectively). Moreover, the percentage of oocytes that matured to the MI stage was higher (P < 0.05) among those injected at 0 hours than among control oocytes and those injected at 24 and 72 hours (45.9 ± 6.8% vs. 22.1 ± 3.5%, 22.8 ± 10.0%, and 10.0 ± 4.4%, respectively). In experiment 3, oocytes were intracytoplasmically microinjected with Wee1B-siRNA at 0 hours of IVM and cultured for 0, 24, 48, or 72 hours. Thereafter, maturation-related gene expression was analyzed by quantitative real-time polymerase chain reaction. Messenger RNA expression of cAMP and cell division cycle 25B was lower (P < 0.05) in oocytes injected at 48 hours than in the other groups. Messenger RNA expression of cAMP was lower (P < 0.05) in oocytes injected at 0 hours than in control oocytes and those injected at 72 hours. Messenger RNA expression of mitogen-activated protein kinase 1 and mitogen-activated protein kinase 3 was higher (P < 0.05) in oocytes injected at 72 hours than in the other groups. In conclusion, we confirmed that Wee1B-siRNA microinjection enhances the percentages of canine oocytes that reach the MI and MII stages. These data suggest that Wee1B-siRNA microinjection could be a useful strategy to obtain mature canine oocytes for research and assisted canine reproduction. Copyright © 2014 Elsevier Inc. All rights reserved.Theriogenology 10/2014; · 1.85 Impact Factor