In Vitro Reconstruction of Xenopus Oocyte Ovulation.

Alexander A Tokmakov,Takumi Isobe,Ken-Ichi Sato,Yuta Matsumoto

doi:10.3390/ijms20194766

Abstract

Progesterone is widely used to induce maturation of isolated fully grown oocytes of the African clawed frog, Xenopus laevis. However, the hormone fails to release oocytes from the layer of surrounding follicle cells. Here, we report that maturation and follicle rupture can be recapitulated in vitro by treating isolated follicular oocytes with progesterone and low doses of the matrix metalloproteinase (MMP), collagenase, which are ineffective in the absence of the steroid. Using this in vitro ovulation model, we demonstrate that germinal vesicle breakdown (GVBD) and oocyte liberation from ovarian follicles occur synchronously during ovulation. Inhibition of the MAPK pathway in these experimental settings suppresses both GVBD and follicular rupture, whereas inhibition of MMP activity delays follicular rupture without affecting GVBD. These results highlight importance of MAPK and MMP activities in the ovulation process and provide the first evidence for their involvement in the release of oocytes from ovarian follicles in frogs. The in vitro ovulation model developed in our study can be employed for further dissection of ovulation.

Highlights

Oocytes of most vertebrate species, including frogs, reside and grow in the ovaries while arrested at the diplotene stage in prophase of the first meiotic division
It is possible that both types of steroids are involved in meiotic maturation of Xenopus oocytes, considering high oocyte levels of CYP17, an enzyme converting progestins to androgens [13,14]
We have found that both maturation and follicle rupture can be recapitulated in vitro in the follicular Xenopus oocytes treated with PG and low concentrations of collagenase, an enzyme of matrix metalloproteinase (MMP) family, (Figure 2), as well as in the oocytes pretreated with collagenase shortly before PG administration (Figure 3)

Summary

Introduction

Oocytes of most vertebrate species, including frogs, reside and grow in the ovaries while arrested at the diplotene stage in prophase of the first meiotic division. PG is suggested to be the major physiological mediator responsible for triggering maturation of frog oocytes because its addition to the isolated defolliculated oocytes at submicromolar and low micromolar concentrations induces meiotic maturation [6,7] and because its intra-oocyte level increases abruptly to micromolar concentrations during meiosis re-entry [8]. This steroid is widely used to induce in vitro oocyte maturation in Xenopus models. It is possible that both types of steroids are involved in meiotic maturation of Xenopus oocytes, considering high oocyte levels of CYP17, an enzyme converting progestins to androgens [13,14]

Methods

Results

Conclusion