内源性逆转录病毒env基因在胎生鱼许氏平鲉胎盘形成中的功能研究

偶然“捕获”内源性逆转录病毒的env（envelope）基因为其所用，是哺乳动物胎盘出现，从卵生进化为胎生的主要驱动力。鱼类是最早进化出胎盘的脊椎动物，但其胎盘多次独立起源及随机分布的机制仍是个谜题。申请者前期研究发现胎生鱼许氏平鲉属于滤泡内妊娠，具有滤泡性胎盘；8个env基因特异性表达于将发育为胎盘的滤泡细胞，其表达量在胎盘形成过程中显著上调，这证明许氏平鲉“招募”env基因参与其适应性生理活动—胎生。基于以上基础，本项目拟解析许氏平鲉滤泡胎盘精细结构及其发育的动态变化过程，从细胞融合、免疫抑制及转录调控三方面探究env基因在滤泡胎盘形成中的功能，阐明许氏平鲉“偶然”捕获env基因“随机”进化出胎盘的机制。研究结果将有助于深入了解脊椎动物胎盘随机出现的潜在机制，作为趋同进化的一个显著例子，也将为脊椎动物物种进化提供重要提示。

“Capture” envelope genes from the endogenous retrovirus for their own physiological function drives the emergence and evolution of placental mammals from egg-laying animals. The earliest origin of vertebrate placenta identified is that of fishes. However, our understanding of the functional mechanics of why placentation emerged independently and in a stochastic manner in several groups of teleost is still lacking. Our previous study showed that black rockfish is a viviparous teleost with intrafollicular gestation owning follicular placenta. Eight env genes were specific expressed in the ovary and were significantly up-regulated during the formation of placenta. In situ hybridization analysis indicated that env genes were expressed in the follicular cells that will later form the follicular placenta in rockfish. We speculate that env gene is “domesticated” to be involved in follicular placenta formation in rockfish. Further experiment needs to be carried out in terms of fusion, immunosuppressive and transcription regulation of env genes to explore how they functions in the placenta formation of rockfish. This will provide the evidence of how placenta evolutionary origins in rockfish. The results could contribute to a deeper understanding of the mechanisms underlying the rare and stochastic emergence of placentation, a remarkable example of evolutionary convergence, and provide hints on species evolution in vertebrates.