Figure 1.

Grb7 triggers an accelerated germinal vesicle breakdown (GVBD) in oocytes deprotected from their layer of surrounding follicular cells and expressing the epidermal growth factor (EGF) receptor (EGFR). The human EGFR was expressed in stage VI Xenopus oocytes surrounded by follicular cells (FCs) and stage VI oocytes deprotected from their follicular cells (DEs, defolliculated oocytes). One hour before EGF stimulation (5 nM) or not in control (Ct), Grb7 was microinjected in the equatorial region at concentrations of 5, 10, 20, or 100 ng. A, Hoechst 33258 staining of the surrounding layer of oocytes with follicular cells (left) or defolliculated (right); the scale bars represent 1000 μm. B, EGFR immunoprecipitations followed by Western blots with anti-EGFR and anti–phospho-tyrosine (P-Tyr). C, example of GVBD of stage VI Xenopus oocytes; the scale bars represent 1000 μm. D and E, the GVBD attesting for the progression from prophase I to metaphase II (maturation) was scored 12 h after stimulation by EGF or not (Ct) in FC and DE oocytes. F, the GVBD₅₀ representing the time required to obtain half of the response of FC and DE oocytes to undergo GVBD was determined. Experiments were performed on 10 to 20 oocytes from three different females. Statistical significance was accepted in DE and FC for ∗p < 0.05.