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The position of the germinal vesicle and the chromatin organization together provide a marker of the developmental competence of mouse antral oocytes

¹ Dipartimento di Biologia Animale, Università degli Studi di Pavia, Piazza Botta 9-10, 27100 Pavia, Italy² Sezione di Istologia e Embriologia, Dipartimento di Medicina Sperimentale, Università degli Studi di Parma, Via Volturno 39, 43100 Parma, Italy³ Fondazione IRCCS, Policlinico San Matteo, Viale Golgi 19, 27100 Pavia, Italy⁴ Centro di Ricerca Interdipartimentale di Ingegneria Tissutale e Centro di Eccellenza in Biologia Applicata, Università degli Studi di Pavia, Via Ferrata 1, 27100 Pavia, Italy

Correspondence should be addressed to M Zuccotti; Email: maurizio.zuccotti{at}unipv.it; S Garagna at Dipartimento di Biologia Animale, Università degli Studi di Pavia; Email: silvia.garagna{at}unipv.it

Based on their chromatin organization, antral oocytes can be classified into two classes, namely surrounded nucleolus (SN, chromatin forms a ring around the nucleolus), and not surrounded nucleolus (NSN, chromatin has a diffuse pattern). Oocytes of both classes are capable of meiotic resumption, but while SN oocytes, following fertilization, develop to term, NSN oocytes never develop beyond the two-cell stage. A recent study has shown that the position of the germinal vesicle (GV) can be used as a morphological marker predictive of oocyte meiotic competence, i.e. oocytes with a central GV have a higher meiotic competence than oocytes with an eccentric GV. In the present study, we have associated both markers with the aim of identifying, with more accuracy, the oocytes' developmental competence. Following their isolation, antral oocytes were classified on the basis of both SN and NSN chromatin configuration and their GV position, matured to metaphase II and fertilized in vitro. We demonstrated that the position of the GV is a good marker to predict the oocytes' developmental competence, but only when associated with the observation of the chromatin organization.