Laboratory of Non-Mendelian Evolution, Institute of Animal Physiology and Genetics, Czech Academy of Sciences, Rumburská 89 , Liběchov 277 21, Czech Republic.
Laboratory of Fish Genetics, Institute of Animal Physiology and Genetics, Czech Academy of Sciences, Rumburská 89 , Liběchov 277 21, Czech Republic.
Biol Lett. 2024 Sep;20(9):20240182. doi: 10.1098/rsbl.2024.0182. Epub 2024 Sep 18.
Among vertebrates, obligate parthenogenesis occurs exclusively in squamate reptiles. Premeiotic endoreplication in a small subset of developing oocytes has been documented as the mechanism of production of unreduced eggs in minutely explored obligate parthenogenetic lineages, namely in teiids and geckos. The situation in the lacertid genus has been discussed for decades. Certain observations suggested that the ploidy level is restored during egg formation through a fusion of egg and polar body nuclei in and . In this study, we re-evaluated the fusion hypothesis by studying diplotene chromosomes in adult females of sexual species and obligate parthenogens and . We revealed 19 bivalents in the sexual species and 38 bivalents in the diploid obligate parthenogens, which uncovers premeiotic endoreplication as the mechanism of the production of non-reduced eggs in parthenogenetic females. The earlier contradicting reports can likely be attributed to the difficulty in identifying mispairing of chromosomes in pachytene, and the fact that in parthenogenetic reptiles relying on premeiotic endoreplication only a small subset of developing oocytes undergo genome doubling and overcome the pachytene checkpoint. This study highlights co-option of premeiotic endoreplication for escape from sexual reproduction in all independent hybrid origins of obligate parthenogenesis in vertebrates studied to date.
在脊椎动物中，强制性孤雌生殖仅发生在有鳞目爬行动物中。在研究较少的强制性孤雌生殖谱系中，即胎生蜥科和壁虎科中，已经记录了一小部分发育中的卵母细胞的减数分裂前内复制，作为产生未减数卵子的机制。关于蜥蜴属的情况已经讨论了几十年。某些观察结果表明，在 和 中，通过卵和极体核的融合，在卵形成过程中恢复了倍性水平。在这项研究中，我们通过研究有性物种 和强制性孤雌生殖 的成年雌性的二价体染色体，重新评估了融合假说。我们在有性物种中发现了 19 个二价体，在二倍体强制性孤雌生殖中发现了 38 个二价体，这揭示了减数分裂前内复制是产生非减数卵子的机制在孤雌生殖雌性中。早期的矛盾报告可能归因于在粗线期难以识别染色体的错配，以及在仅依赖减数分裂前内复制的孤雌生殖爬行动物中，只有一小部分发育中的卵母细胞经历基因组加倍并克服粗线期检查点。这项研究强调了在迄今为止研究的所有独立起源的强制性孤雌生殖的脊椎动物中，减数分裂前内复制被选择用于逃避有性繁殖。
