Dedukh Dmitrij, Lisachov Artem, Panthum Thitipong, Singchat Worapong, Matsuda Yoichi, Imai Yukiko, Janko Karel, Srikulnath Kornsorn
Laboratory of Non-Mendelian Evolution, Institute of Animal Physiology and Genetics, Czech Academy of Sciences, Liběchov, Czechia.
Animal Genomics and Bioresource Research Unit (AGB Research Unit), Faculty of Science, Kasetsart University, Bangkok, Thailand.
Front Cell Dev Biol. 2024 Aug 23;12:1465335. doi: 10.3389/fcell.2024.1465335. eCollection 2024.
Reproductive isolation and hybrid sterility are mechanisms that maintain the genetic integrity of species and prevent the introgression of heterospecific genes. However, crosses of closely related species can lead to complex evolution, such as the formation of all-female lineages that reproduce clonally. Bighead catfish () and North African catfish () diverged 40 million years ago. They are cultivated and hybridized in Thailand for human consumption. Male hybrids are sterile due to genome-wide chromosome asynapsis during meiosis. Although female hybrids are sometimes fertile, their chromosome configuration during meiosis has not yet been studied.
We analyzed meiosis in the hybrid female catfish at pachytene (synaptonemal complexes) and diplotene (lampbrush chromosomes), using immunostaining to detect chromosome pairing and double-stranded break formation, and FISH with species-specific satellite DNAs to distinguish the parental chromosomes.
More than 95% of oocytes exhibited chromosome asynapsis in female hybrid catfish; however, they were able to progress to the diplotene stage and form mature eggs. The remaining oocytes underwent premeiotic endoreplication, followed by synapsis and crossing over between sister chromosomes, similar to known clonal lineages in fish and reptiles.
The occurrence of clonal reproduction in female hybrid catfish suggests a unique model for studying gametogenic alterations caused by hybridization and their potential for asexual reproduction. Our results further support the view that clonal reproduction in certain hybrid animals relies on intrinsic mechanisms of sexually reproducing parental species, given their multiple independent origins with the same mechanism.
生殖隔离和杂种不育是维持物种遗传完整性并防止异种基因渗入的机制。然而，近缘物种的杂交会导致复杂的进化，例如形成无性繁殖的全雌系。大口鲶（）和北非鲶鱼（）在4000万年前分化。它们在泰国被养殖并杂交以供人类食用。雄性杂种由于减数分裂期间全基因组染色体不联会而不育。尽管雌性杂种有时可育，但其减数分裂期间的染色体构型尚未得到研究。
我们分析了杂种雌性鲶鱼在粗线期（联会复合体）和双线期（灯刷染色体）的减数分裂，使用免疫染色检测染色体配对和双链断裂形成，并利用物种特异性卫星DNA进行荧光原位杂交以区分亲本染色体。
超过95%的卵母细胞在杂种雌性鲶鱼中表现出染色体不联会；然而，它们能够进入双线期并形成成熟卵子。其余卵母细胞经历减数分裂前的核内复制，随后姐妹染色体之间发生联会和交叉，这与鱼类和爬行动物中已知的克隆系相似。
杂种雌性鲶鱼中克隆繁殖的出现为研究杂交引起的配子发生改变及其无性繁殖潜力提供了一个独特模型。我们的结果进一步支持了这样一种观点，即某些杂种动物中的克隆繁殖依赖于有性繁殖亲本物种的内在机制，因为它们具有相同机制的多个独立起源。
