Abstract：
In most eukaryotes, pairing of homologous chromosomes is an essential feature of meiosis that ensures homologous recombination and segregation. However, when the pairing process begins, it is still under investigation. Contrasting data exists in Mus musculus, since both leptotene DSB-dependent and preleptotene DSB-independent mechanisms have been described. To unravel this contention, we examined homologous pairing in pre-meiotic and meiotic Mus musculus cells using a three-dimensional fluorescence in situ hybridization-based protocol, which enables the analysis of the entire karyotype using DNA painting probes. Our data establishes in an unambiguously manner that 73.83% of homologous chromosomes are already paired at premeiotic stages (spermatogonia-early preleptotene spermatocytes). The percentage of paired homologous chromosomes increases to 84.60% at mid-preleptotene-zygotene stage, reaching 100% at pachytene stage. Importantly, our results demonstrate a high percentage of homologous pairing observed before the onset of meiosis; this pairing does not occur randomly, as the percentage was higher than that observed in somatic cells (19.47%) and between nonhomologous chromosomes (41.1%). Finally, we have also observed that premeiotic homologous pairing is asynchronous and independent of the chromosome size, GC content, or presence of NOR regions.
摘要：
在大多数真核生物中，同源染色体的配对是减数分裂的一个重要特征，确保同源重组和分离。然而,当配对过程开始时，它仍在调查中。对比数据存在于小家鼠中，因为已经描述了leptoteneDSB依赖性和leptoteneDSB无关的机制。为了解开这个争论，我们使用基于三维荧光原位杂交的方案检查了减数分裂前和减数分裂小家鼠细胞的同源配对，这使得能够使用DNA绘画探针分析整个核型。我们的数据以明确的方式确定了73.83％的同源染色体已经在减数分裂前期（精原细胞-早期前精母细胞）配对。配对同源染色体的百分比在前期-受精卵阶段增加到84.60％，在粗品阶段达到100%。重要的是,我们的结果表明，在减数分裂开始之前观察到的同源配对比例很高;这种配对不是随机发生的，因为该百分比高于在体细胞（19.47％）和非同源染色体之间（41.1％）观察到的百分比。最后,我们还观察到，减数分裂前同源配对是异步的，并且与染色体大小无关，GC含量,或存在NOR区域。
