Characterization of MPF and MAPK Activities during Meiotic Maturation of Xenopus tropicalis Oocytes

Abstract

Resumption of meiosis in oocytes of Xenopus tropicalis required translation but not transcription, and was marked by the appearance of a white spot and a dark ring, coincident with entry into metaphase I and the onset of anaphase I, respectively. Cyclin B(2)/p34(cdc2) activity increased prior to the first meiotic division, declined at the onset of anaphase I, and subsequently increased again. The capacity of egg cytoplasm to induce germinal vesicle breakdown (GVBD) was inhibited by cycloheximide, despite the fact that these oocytes contained cyclin B(2)/p34(cdc2) complexes. However, cycloheximide-treated oocytes underwent GVBD following injection of constitutively active mitogen-activated protein kinase (MAPK) kinase 2 (MEK2), p33(Ringo), or Delta 90 cyclin B. MAPK activity increased just prior to the first meiotic division and remained stable thereafter. Although injection of constitutively active MEK2 induced GVBD, treatment with the MEK inhibitors U0126 or anthrax lethal factor delayed GVBD and prevented spindle formation. Interestingly, the ability of egg cytoplasm to induce GVBD was unaffected by the inhibition of MEK activity. Our results indicate that the synthesis of a novel or short-lived protein(s) which acts in a MEK-independent fashion is required in order for egg cytoplasm to induce GVBD in X. tropicalis oocytes.

Xenopus laevis oocyte maturation is affected by metal chlorides

“…Nevertheless, amphibian early embryos, and presumably oocytes, lack DNA damage checkpoint and fail to respond to DNA breaks (Anderson et al, 1997;Finkielstein et al, 2001). Then, due to the specificity of our cellular model (Bodart et al, 2002), other mechanisms than those including DNA damage response or transcription inhibition, have to be involved in the G2/M modulation observed. For instance, the inhibition of G2/M transition may rely on inhibition of protein synthesis, an effect that has been observed for cadmium exposure in liver (Smalinskiene et al, 2005).…”

“…laevis oocyte has been used for decades as a model for studying calcium signaling (Delisle, 1991;DeLisle and Welsh, 1992;Marin, 2012;Marin et al, 2010), cell cycle transitions (Bodart et al, 2002;Heikkila et al, 2007;Machaca, 2007). However, this model has been seldom used in toxicological studies in spite of the advantages provided by different species of Xenopus genus (Khokha, 2012;Schultz and Dawson, 2003).…”

Xp42Mpk1 Activation Is Not Required for Germinal Vescicle Breakdown but for Raf Complete Phosphorylation in Insulin-stimulated Xenopus Oocytes

“…Mos synthesis, cyclin B2 phosphorylation was assessed, because the latter is relevant for MPF activity (36,37). In prophase-arrested oocytes, cyclin B2 is detected as a doublet of two isoforms, corresponding to the non-phosphorylated form of the protein whereas, upon hormonal stimulation, cyclin B2 is only detected under its sole phosphorylated form.…”

Discrimination of the Roles of MPF and MAP Kinase in Morphological Changes That Occur during Oocyte Maturation

“…In Xenopus oocytes, the inhibition of MAPK by U0126 before progesterone treatment prevented spindle formation (Gross et al, 2000;Bodart et al, 2002). Oocytes from c-mosknockout mice extruded abnormal polar bodies (Verlhac et al, 1996;Choi et al, 1996) (see also reviews Sagata, 1997;Abrieu et al, 2001).…”