Unusual cytoskeletal and chromatin configurations in mouse oocytes that are atypical in meiotic progression

Meiotic maturation progresses atypically in oocytes of strain LT/Sv and I/LnJ mice. LT/Sv occytes show a high frequency of metaphase I-arrest and parthenogenetic activation. I/LnJ oocytes display retarded kinetics of meiotic maturation and a high frequency of metaphase I-arrest. Some I/LnJ oocytes fail to resume meiosis. Changes in the configuration of chromatin, microtubules, and centrosomes are associated with specific stages of meiotic progression. In this study, the configuration of these subcellular components was examined in LT/Sv, I/LnJ, and C57BL/6J (control) oocytes either freshly isolated from large antral follicles or after culture for 15 hr to allow progression of spontaneous meiotic maturation. Differences were found in the organization of chromatin, microtubules, and centrosomes in LT/Sv and I/LnJ oocytes compared to control oocytes. For example, rather than exhibiting multiple cytoplasmic and nuclear centrosomes as in the normal germinal vesicle-stage oocytes, LT/Sv oocytes typically contain a single large centrosome. In contrast, I/LnJ oocytes displayed many small centrosomes. The microtubules of normal germinal vesicle-stage oocytes were organized as arrays or asters, but microtubules were shorter in LT/Sv oocytes and absent from I/LnJ oocytes. After a 15-hr culture, centrosomal material of normal metaphase II oocytes was organized at both spindle poles. In contrast, metaphase I-arrested LT/Sv oocytes exhibited an elongated spindle with centrosomal material appearing more organized at one pole of the spindle. Both control and LT/Sv oocytes displayed cytoplasmic centrosomes.(ABSTRACT TRUNCATED AT 250 WORDS)