Reorganisation of Cell Cytoskeleton of Cat Oocytes Matured in vitro

Abstract

Developmental capacity of domestic cat oocyte matured in vitro is poor when compared to that of in vivo matured oocyte. While cytoplasmic maturation of the oocytes is essentially required for embryo development, little is really known about distribution of cell components during the course of in vitro maturation (IVM). The aims of this study were to examine and to describe the changes in the distribution of microtubule and actin microfilaments in relation to stage of nuclear maturation during IVM. Cumulus oocyte complexes were matured in vitro for 0, 6, 12, 18 and 24 h and then labeled with immunofluorescent dyes against microtubules, actin microfilaments and chromatin to enable examination of a series of changes in nuclear and cytoplasmic maturation. A total of 302 oocytes were examined with a confocal laser scanning microscope. Immature oocytes were arrested at germinal vesicle stage for approximately 6-12 h, where actin microfilaments were typically distributed throughout the ooplasm. Metaphase I plate (meiotic spindles) was then completely formed by 12-18 h. The meiotic spindle and actin microfilaments facilitated segregation of the homologous chromosomes resulting in extrusion of the first polar body. The second meiotic spindle was soon established, and the oocytes then finally reached MII stage. In conclusion, this study described a series of nuclear and cytoplasmic changes during in vitro maturation of cat oocytes. Nuclear maturation of cat oocytes asynchronously resumed and reached metaphase II, while examination of the oocytes every 6 h was sufficient to evaluate the redistribution of microtubules and actin microfilaments during the course of nuclear maturation.