Eijpe M, Offenberg H, Goedecke W, Heyting C
Laboratory of Genetics, Wageningen University and Research Centre, The Netherlands.
Chromosoma. 2000;109(1-2):123-32. doi: 10.1007/s004120050420.
Synaptonemal complexes (SCs) are zipperlike structures that are assembled between homologous chromosomes during meiotic prophase. They consist of two axial elements (AEs) (one along each of the two homologous chromosomes), which, in mature SCs, are connected by numerous transverse filaments along their length. Several proteins involved in the later steps of meiotic recombination most probably function in close association with the AEs of SCs, because the proteins involved in these steps have all been localised along AEs or SCs by immunocytochemical methods. It is not known at which step in meiotic recombination this association with the AEs is established. In order to shed some light on this issue, we analysed the localisation of two proteins that are involved in early steps of meiotic recombination, RAD50 and MRE11, relative to AEs and SCs by immunofluorescence labelling of paraffin sections of the mouse testis, using affinity-purified polyclonal antibodies against RAD50 and MRE11, and monoclonal and polyclonal antibodies against SC components. The localisation patterns of MRE11 and RAD50 within spermatocytes were very similar. MRE11 and RAD50 appeared in high abundance in preleptotene spermatocytes, just before SC components could be detected. From preleptotene until early zygotene they were present throughout the nucleus. In mid and late zygotene, MRE11 and RAD50 concentrated in distinct areas; in early pachytene the two proteins had almost disappeared from the nucleus, except from the sex vesicle (the chromatin of the XY bivalent), where they persisted in high abundance until diplotene. We propose that MRE11 and RAD50, together with other proteins, prepare chromatin throughout the early meiotic prophase nucleus for the initiation of meiotic recombination. Possibly, only a small fraction of the RAD50- and MRE11-containing (pre)recombination complexes associates transiently with AEs, where further steps in meiotic recombination can take place.
联会复合体（SCs）是在减数分裂前期同源染色体之间组装形成的拉链状结构。它们由两个轴元件（AEs）组成（分别沿着两条同源染色体中的每一条），在成熟的SCs中，这两个轴元件沿着其长度由众多横向细丝相连。减数分裂重组后期步骤中涉及的几种蛋白质很可能与SCs的AEs紧密相关，因为通过免疫细胞化学方法已将参与这些步骤的蛋白质定位到AEs或SCs上。目前尚不清楚在减数分裂重组的哪个步骤中建立了与AEs的这种关联。为了阐明这个问题，我们通过对小鼠睾丸石蜡切片进行免疫荧光标记，使用针对RAD50和MRE11的亲和纯化多克隆抗体以及针对SC成分的单克隆和多克隆抗体，分析了参与减数分裂重组早期步骤的两种蛋白质RAD50和MRE11相对于AEs和SCs的定位。MRE11和RAD50在精母细胞内的定位模式非常相似。在细线前期精母细胞中，就在能够检测到SC成分之前，MRE11和RAD50大量出现。从细线前期到偶线期早期，它们遍布整个细胞核。在偶线期中后期，MRE11和RAD50集中在不同区域；在粗线期早期，这两种蛋白质几乎从细胞核中消失，除了性泡（XY二价体的染色质），在那里它们一直大量存在直到双线期。我们提出，MRE11和RAD50与其他蛋白质一起，在减数分裂前期早期的整个细胞核中为减数分裂重组的启动准备染色质。可能只有一小部分含有RAD50和MRE11的（预）重组复合体与AEs短暂结合，减数分裂重组的后续步骤可能在此发生。
