UNUSUAL CYTOSKELETAL AND CHROMATIN CONFIGURATIONS IN MOUSE OOCYTES THAT ARE ATYPICAL IN MEIOTIC PROGRESSION

Meiotic maturation progresses atypically in oocytes of strain LT/Sv an d I/LnJ mice. LT/Sv occytes show a high frequency of metaphase I-arres t and parthenogenetic activation. I/LnJ oocytes display retarded kinet ics of meiotic maturation and a high frequency of metaphase I-arrest. Some I/LnJ oocytes fail to resume meiosis. Changes in the configuratio n of chromatin, microtubules, and centrosomes are associated with spec ific stages of meiotic progression. In this study, the configuration o f these subcellular components was examined in LT/Sv, I/LnJ, and C57BL /6J (control) oocytes either freshly isolated from large antral follic les or after culture for 15 hr to allow progression of spontaneous mei otic maturation. Differences were found in the organization of chromat in, microtubules, and centrosomes in LT/Sv and I/LnJ oocytes compared to control oocytes. For example, rather than exhibiting multiple cytop lasmic and nuclear centrosomes as in the normal germinal vesicle-stage oocytes, LT/Sv oocytes typically contain a single large cencentrosome . In contrast, I/LnJ oocytes displayed many small centrosomes. The mic rotubules of normal germinal vesicle-stage oocytes were organized as a rrays or asters, but microtubules were shorter in LT/Sv oocytes and ab sent from I/LnJ oocytes. After a 15-hr culture, centrosomal material o f normal metaphase II oocytes was organized at both spindle poles. In contrast, metaphase I-arrested LT/Sv oocytes exhibited an elongated sp indle with centrosomal material appearing more organized at one pole o f the spindle. Both control and LT/Sv oocytes displayed cytoplasmic ce ntrosomes. Metaphase I-arrested I/LnJ oocytes rarely had cytoplasmic c entrosomes but exhibited centrosomal foci at the spindle periphery. Th us, oocytes that are atypical in the progression of meiotic maturation displayed aberrant configurations of microtubules and centrosomes, wh ich are thought to participate in the regulation of meiotic maturation . (C) 1995 Wiley-Liss, Inc.