Nath Shivangi, Welch Lucille A, Flanagan Mary K, White Michael A
Department of Genetics, University of Georgia, 120 Green St, Athens, GA, 30602, USA.
Chromosome Res. 2022 Dec;30(4):429-442. doi: 10.1007/s10577-022-09699-0. Epub 2022 May 30.
Double-strand break repair during meiosis is normally achieved using the homologous chromosome as a repair template. Heteromorphic sex chromosomes share little sequence homology, presenting unique challenges to the repair of double-strand breaks. Our understanding of how heteromorphic sex chromosomes behave during meiosis has been focused on ancient sex chromosomes, where the X and Y differ markedly in overall structure and gene content. It remains unclear how more recently evolved sex chromosomes that share considerably more sequence homology with one another pair and form double-strand breaks. One possibility is barriers to pairing evolve rapidly. Alternatively, recently evolved sex chromosomes may exhibit pairing and double-strand break repair that more closely resembles that of their autosomal ancestors. Here, we use the recently evolved X and Y chromosomes of the threespine stickleback fish (Gasterosteus aculeatus) to study patterns of pairing and double-stranded break formation using molecular cytogenetics. We found that the sex chromosomes of threespine stickleback fish did not pair exclusively in the pseudoautosomal region. Instead, the chromosomes fully paired in a non-homologous fashion. To achieve this, the X chromosome underwent synaptic adjustment during pachytene to match the axis length of the Y chromosome. Double-strand break formation and repair rate also matched that of the autosomes. Our results highlight that recently evolved sex chromosomes exhibit meiotic behavior that is reminiscent of autosomes and argues for further work to identify the homologous templates that are used to repair double-strand breaks on the X and Y chromosomes.
减数分裂过程中的双链断裂修复通常利用同源染色体作为修复模板来实现。异形性染色体的序列同源性很低，这给双链断裂的修复带来了独特的挑战。我们对于异形性染色体在减数分裂过程中行为的理解一直集中在古老的性染色体上，其中X染色体和Y染色体在整体结构和基因含量上有显著差异。目前尚不清楚，那些彼此之间序列同源性高得多的最近进化出的性染色体是如何配对并形成双链断裂的。一种可能性是配对障碍迅速进化。另一种可能性是，最近进化出的性染色体可能表现出更类似于其常染色体祖先的配对和双链断裂修复方式。在这里，我们利用三刺鱼（Gasterosteus aculeatus）最近进化出的X染色体和Y染色体，通过分子细胞遗传学来研究配对模式和双链断裂形成情况。我们发现，三刺鱼的性染色体并非仅在拟常染色体区域配对。相反，这些染色体以非同源的方式完全配对。为了实现这一点，X染色体在粗线期进行了突触调整，以匹配Y染色体的轴长。双链断裂的形成和修复速率也与常染色体的情况相匹配。我们的研究结果表明，最近进化出的性染色体表现出类似于常染色体的减数分裂行为，并主张开展进一步工作来确定用于修复X染色体和Y染色体上双链断裂的同源模板。
