Microtubule and microfilament organization in maturing human oocytes

Various stages of immature human oocytes were imaged for microtubule, microfilament and chromatin organization. After germinal vesicle breakdown, a small microtubule aster was observed near the condensed chromatin. The asters appeared to elongate and encompass the condensed chromatin. At metaphase I stage, microtubules were detected in the meiotic spindle. The meiotic spindle in metaphase II was a symmetric, barrel-shaped structure containing anastral broad poles, located peripherally and radially oriented. After germinal vesicle breakdown, treatment with taxol induced numerous cytoplasmic foci of microtubules, mainly in the cortex of the oocyte. Microfilaments were observed as a relatively thick uniform area around the cell cortex and were also found near the germinal vesicle position. After germinal vesicle breakdown, the microfilaments were seen in both the cortex and around the female chromatin. In conclusion, this study suggests that both microtubules and microfilaments are closely associated with the reconstruction and proper positioning of chromatin after germinal vesicle breakdown and during meiotic maturation in human oocytes.