Molecular Population Genetics and Breeding Group, Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore, 117604, Singapore.
School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore, 637551, Singapore.
Mar Biotechnol (NY). 2021 Apr;23(2):201-214. doi: 10.1007/s10126-020-10015-2. Epub 2021 Feb 12.
Sexual dimorphism is common across the animal kingdom. Knowledge of the mechanisms of sexual size dimorphism is limited although it is important in biology and aquaculture. Tilapia is the common name for ~ 100 species of cichlid fish. Some are important aquaculture species and males outgrow females. To gain novel insights into the mechanisms underlying sexual size dimorphism, we analyzed the differences of brain transcriptomes between males and females in Mozambique tilapia and studied the function of the pro-opiomelanocortin (Pomc) gene in tilapia and zebrafish. The transcriptome analysis identified 123, 55, and 2706 sex-biased genes at 5, 30, and 90 dph (days post-hatch), respectively, indicating sexual dimorphism of gene expressions in the brain. The expression of Pomc in the tilapia brain was a female-biased at 30, 90, and 120 dph. An analysis of the DNA sequence located upstream of the tilapia Pomc transcriptional start site identified two estrogenic response elements. In vitro luciferase assay of the two elements revealed that β-estradiol significantly enhanced the expression of luciferase activity, suggesting that the expression of Pomc is mediated by estrogen. We knocked out Pomc in zebrafish using Crispr/Cas-9. The Pomc-knockout zebrafish showed faster growth and higher sensitivity to feeding as compared to the wild-type fish. Taken together, our results indicate that Pomc contributes to sexual size dimorphism and suggest that the high estrogen level in females promotes the expression of Pomc and suppresses feeding in female tilapias, which leads to the slower growth of female tilapias.
性二型是动物界中普遍存在的现象。尽管性大小二型在生物学和水产养殖中很重要，但人们对其机制的了解有限。罗非鱼是约 100 种慈鲷鱼的通用名称。有些是重要的水产养殖物种，雄性比雌性生长得更大。为了深入了解性大小二型的机制，我们分析了莫桑比克罗非鱼雌雄个体之间的大脑转录组差异，并研究了 pro-opiomelanocortin (Pomc) 基因在罗非鱼和斑马鱼中的功能。转录组分析分别在 5、30 和 90 dph（孵化后天数）确定了 123、55 和 2706 个性别偏向基因，表明大脑中基因表达存在性二型。罗非鱼脑中 Pomc 的表达在 30、90 和 120 dph 时呈雌性偏倚。对罗非鱼 Pomc 转录起始位点上游的 DNA 序列进行分析，确定了两个雌激素反应元件。体外荧光素酶测定两个元件的活性表明，β-雌二醇显著增强了荧光素酶活性的表达，提示 Pomc 的表达受雌激素调节。我们使用 Crispr/Cas-9 在斑马鱼中敲除了 Pomc。与野生型鱼相比，Pomc 敲除的斑马鱼生长更快，对摄食的敏感性更高。总之，我们的研究结果表明，Pomc 参与了性大小二型，并提示雌鱼中高水平的雌激素促进了 Pomc 的表达，抑制了雌罗非鱼的摄食，导致雌罗非鱼生长缓慢。
