Meiotic Progression of Sheep Oocytes from Preantral Follicles with Two Different Sizes

Background: Oocyte nuclear and cytoplasmic maturation aregradually acquired during folliculogenesis in vivo. One of theoocyte in vitro maturation challenges is heterozygous populationof oocytes which have different nuclear and cytoplasmicpotential. We aim to investigate meiotic progression of sheepoocytes from preantral follicles with two different sizes.Materials and Methods: Cumulus oocyte complexes wereisolated by puncturing ۲ to ۴ mm and ۴ to ۶ mm diameter follicles,and then were cultured for ۰ to ۲۴h maturation in M۱۹۹.For assessing meiotic progression, oocytes were fixed in ۴%paraformaldehyde and stained with Hoechst. Meiotic progressionwas classified into germinal vesicle (GV), germinal vesiclebreakdown and metaphase I, II stages. The percentages of GVin different hours of maturation were compared between twofollicular sizes.Results: In ۲-۴ mm group, the percentage of GV oocyte in ۲,۴, ۶, ۸, ۱۰, ۱۲, and ۲۴ h of maturation was ۹۲.۷۴, ۹۴.۴, ۹۸.۳۳,۷۶.۳۱, ۵۳.۴۰, ۳۳.۸, ۲۴.۳۰, and ۲۰.۹۵, respectively. The correspondingpercentage for ۴-۶ mm group was ۹۷.۳۳, ۹۶.۶۷,۹۶.۶۷, ۷۸, ۶۷.۶۷, ۵۴.۳۳, ۳۴.۳۳, and ۲۰.۳۳, respectively. Rescueof meiosis occurs faster in oocytes with ۲-۴ mm follicular diameteras it is observed that after ۱۰h of maturation ۵۳.۴۰% of۲-۴ mm group and ۶۷.۶۷% of ۴-۶ mm group remain in GV state(P<۰.۰۵).Conclusion: This study provides evidence that different follicularstages have different meiotic progression, thus the selectionof appropriate follicles for in vitro maturation requiresfurther study.

کلیدواژه ها:

Meiotic Progression ، Preantral Follicles ، Maturation ، Oocyte