Can A, Semiz O, Cinar O
Laboratory for Reproductive Cell Science, Department of Histology-Embryology, Ankara University School of Medicine, Ankara, Sihhiye, 06339, Turkey.
Mol Hum Reprod. 2003 Dec;9(12):749-56. doi: 10.1093/molehr/gag093.
Centrosomes, major regulatory sites for the microtubule (MT) nucleation, are regulated in a dynamic manner throughout the process of meiotic maturation. Recently, centrosome orientation in mouse oocytes has been demonstrated in metaphase I through metaphase II. However, centrosomal protein expression in concordance with MT polymerization in earlier stages of oocyte maturation from germinal vesicle stage (GV) to prometaphase I still remains unclear. The present study aims to assess the centrosome-microtubule remodelling during the onset of meiosis based on strict criteria of nuclear maturation. Six consecutive stages were determined for scoring the oocytes as unrimmed nucleolus (UR), partially rimmed nucleolus (PR), fully rimmed nucleolus (FR), nuclear lamina dissolution (NLD), disappearance of nucleolus (DON), and chromatin condensation (CC). A centrosomal protein, pericentrin, was found tightly localized adjacent to nuclear lamina in UR, lacking any MT nucleation activity. In concordance with the competency to resume meiosis, an increase in the amount and nucleation capacity of pericentrin is noted. In FR, cytoplasmic MT almost disappeared while de-novo microtubule polymerization was found in small aggregates of pericentrin localized around the nucleus. Towards the end of DON and CC, a sudden burst of pericentrin was noted with an extreme MT nucleation activity in an organized fashion that is essential for the rapid formation of first meiotic spindle. The results show that centrosomes display precisely controlled spatio-temporal changes during the onset of meiotic maturation. Accumulation of centrosomal proteins to a single locus followed by a sequestration to several spots might be evidence of a mechanism by which the proper distribution of centrosomal material during nuclear breakdown and subsequently formation of spindle are regulated in concordance with the nuclear maturation.
中心体是微管（MT）成核的主要调控位点，在减数分裂成熟过程中受到动态调控。最近，已证明小鼠卵母细胞从减数分裂中期I到中期II的中心体方向。然而，从生发泡期（GV）到减数分裂前期I的卵母细胞成熟早期阶段，中心体蛋白表达与MT聚合的一致性仍不清楚。本研究旨在基于严格的核成熟标准，评估减数分裂开始时中心体-微管的重塑情况。确定了六个连续阶段，用于将卵母细胞评分如下：未边缘化核仁（UR）、部分边缘化核仁（PR）、完全边缘化核仁（FR）、核膜溶解（NLD）、核仁消失（DON）和染色质凝聚（CC）。发现一种中心体蛋白，即中心体蛋白，在UR中紧密定位于核膜附近，缺乏任何MT成核活性。随着恢复减数分裂能力的出现，中心体蛋白的数量和成核能力增加。在FR中，细胞质MT几乎消失，而在围绕细胞核定位的中心体蛋白小聚集体中发现了从头微管聚合。在DON和CC接近尾声时，观察到中心体蛋白突然爆发，具有极端的MT成核活性，呈有组织的方式，这对于第一次减数分裂纺锤体的快速形成至关重要。结果表明，在减数分裂成熟开始时，中心体表现出精确控制的时空变化。中心体蛋白在单个位点积累，随后隔离到几个位点，这可能是一种机制的证据，通过该机制，中心体物质在核破裂期间的正确分布以及随后纺锤体的形成与核成熟协调调节。
