Jue Nathaniel K, Foley Robert J, Reznick David N, O'Neill Rachel J, O'Neill Michael J
Institute for Systems Genomics and Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269.
Department of Biology, University of California, Riverside, CA 92521.
G3 (Bethesda). 2018 Jul 2;8(7):2181-2192. doi: 10.1534/g3.118.200270.
The evolution of the placenta is an excellent model to examine the evolutionary processes underlying adaptive complexity due to the recent, independent derivation of placentation in divergent animal lineages. In fishes, the family Poeciliidae offers the opportunity to study placental evolution with respect to variation in degree of post-fertilization maternal provisioning among closely related sister species. In this study, we present a detailed examination of a new reference transcriptome sequence for the live-bearing, matrotrophic fish, , from multiple-tissue RNA-seq data. We describe the genetic components active in liver, brain, late-stage embryo, and the maternal placental/ovarian complex, as well as associated patterns of positive selection in a suite of orthologous genes found in fishes. Results indicate the expression of many signaling transcripts, "non-coding" sequences and repetitive elements in the maternal placental/ovarian complex. Moreover, patterns of positive selection in protein sequence evolution were found associated with live-bearing fishes, generally, and the placental , specifically, that appear independent of the general live-bearer lifestyle. Much of the observed patterns of gene expression and positive selection are congruent with the evolution of placentation in fish functionally converging with mammalian placental evolution and with the patterns of rapid evolution facilitated by the teleost-specific whole genome duplication event.
胎盘的进化是一个很好的模型，可用于研究适应性复杂性背后的进化过程，因为胎盘形成在不同动物谱系中是近期独立衍生的。在鱼类中，食蚊鱼科提供了一个机会，可就密切相关的姐妹物种之间受精后母体供应程度的差异来研究胎盘进化。在本研究中，我们根据多组织RNA测序数据，对卵胎生、母性营养型鱼类的一个新的参考转录组序列进行了详细分析。我们描述了在肝脏、大脑、晚期胚胎以及母体胎盘/卵巢复合体中活跃的遗传成分，以及在鱼类中发现的一组直系同源基因中的相关正选择模式。结果表明，母体胎盘/卵巢复合体中有许多信号转录本、“非编码”序列和重复元件表达。此外，一般在卵胎生鱼类中，特别是在胎盘食蚊鱼中发现了蛋白质序列进化中的正选择模式，这些模式似乎独立于一般的卵胎生生活方式。观察到的许多基因表达和正选择模式与鱼类胎盘形成的进化相一致，在功能上与哺乳动物胎盘进化趋同，并且与硬骨鱼特异性全基因组复制事件促进的快速进化模式一致。
