Dunleavy Elaine M, Collins Caitríona M
Centre for Chromosome Biology, Biomedical Sciences, National University of Ireland, Galway, Ireland.
Prog Mol Subcell Biol. 2017;56:357-375. doi: 10.1007/978-3-319-58592-5_15.
In sexually reproducing organisms the germ line is the cellular lineage that gives rise to gametes. All germ cells originate from germline stem cells that divide asymmetrically to generate gonial pre-cursors, which are amplified in number by mitotic divisions, undergo meiosis and eventually differentiate into mature gametes (haploid eggs and sperm). Information transmitted with gametes is inherited by offspring, and potentially by subsequent generations, instructing in organismal development and beyond. Meiosis comprises one round of DNA replication, followed by two rounds of chromosome segregation; homologous chromosomes segregate in the first division (meiosis I) and sister chromatids segregate in the second division (meiosis II). Important mechanistic features of meiosis occur in substages of prophase I and are critical for genetic recombination, including pairing and synapsis of homologous chromosomes (at leptotene and zygotene), crossing-over (at pachytene), and the appearance of chiasmata (at diplotene/diakinesis). Another unique feature of meiosis is the altered centromere/kinetochore geometry at metaphase I, such that sister kinetochores face the same spindle pole (mono-orientation) and stay together at anaphase I. This chapter reviews centromere dynamics in germ cells, focusing on centromere function and assembly in meiotic cell cycles, as well as centromere inheritance in zygotes. Centromeres are functionally defined by the presence of the histone H3 variant CENP-A, the epigenetic determinant of centromere identity. In most eukaryotes, it is well established that CENP-A function is essential for chromosome segregation in mitosis. CENP-A function in meiosis is less well understood and emerging insights into the differential regulation of meiotic and mitotic CENP-A are discussed.
在有性生殖生物中，生殖系是产生配子的细胞谱系。所有生殖细胞都起源于生殖系干细胞，这些干细胞不对称分裂产生生殖前体细胞，后者通过有丝分裂增加数量，进行减数分裂并最终分化为成熟配子（单倍体卵子和精子）。配子传递的信息由后代继承，并可能由随后的世代继承，指导生物体的发育及其他方面。减数分裂包括一轮DNA复制，随后是两轮染色体分离；同源染色体在第一次分裂（减数分裂I）中分离，姐妹染色单体在第二次分裂（减数分裂II）中分离。减数分裂的重要机制特征发生在前期I的亚阶段，对遗传重组至关重要，包括同源染色体的配对和联会（细线期和偶线期）、交叉互换（粗线期）以及交叉点的出现（双线期/终变期）。减数分裂的另一个独特特征是在中期I时着丝粒/动粒几何结构发生改变，使得姐妹动粒面向同一纺锤体极（单极定向），并在后期I保持在一起。本章回顾生殖细胞中的着丝粒动态，重点关注减数分裂细胞周期中的着丝粒功能和组装，以及合子中的着丝粒遗传。着丝粒在功能上由组蛋白H3变体CENP - A的存在定义，CENP - A是着丝粒身份的表观遗传决定因素。在大多数真核生物中，CENP - A功能对于有丝分裂中的染色体分离至关重要，这一点已得到充分证实。CENP - A在减数分裂中的功能了解较少，本文将讨论对减数分裂和有丝分裂CENP - A差异调节的新见解。
