Pomc Plays an Important Role in Sexual Size Dimorphism in Tilapia

Abstract

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.

Tissue-Specific Expression Pattern in Ancherythroculter nigrocauda, a Sexually Size Dimorphic Fish

“…When fishes reach sexual maturity, the brain’s differentiation in both sexes is completed due to exposure to different sex steroid hormones. Previous studies have reported Pomc as a candidate gene for SSD in tilapia ( Wan et al, 2021 ). Its high expression in the female tilapia brain has been associated with the slow growth of the fish ( Wan et al, 2021 ).…”

Genome editing and its applications in genetic improvement in aquaculture

“…To knockout one target gene/sequence, it is essential that several sgRNAs are designed to ensure high successful rate of knockout. 60 After getting Cas9 and sgRNAs, they are mixed (e.g. 250 ng/µl Cas9 and 200 ng/µl of sgRNA in RNase free water) in a final volume of 5 µl.…”

“…250 ng/µl Cas9 and 200 ng/µl of sgRNA in RNase free water) in a final volume of 5 µl. 60 One nanoliter of the mixture is injected into fertilised eggs at the one-cell stage. Usually, one-cell fertilised eggs are obtained with artificial insemination.…”

“…To allow GE to play a greater role in aquaculture breeding, it is essential to identify and functionally analyse genes identified by QTL mapping or GWAS, 6,7 as well as the function of genes identified from the researches on the regulation signal pathways for the formation of traits. 60,104 Due to the conservation of gene functions during evolution, 105 genes found in model organisms and livestock may be used as candidates for genome editing. 106 Furthermore, most economically important traits (e.g.…”

“…Genome editing helps to increase selection accuracy. Genome editing is widely used to analyse the functions of candidate genes in model organisms, including zebrafish 60 and also in aquaculture species. 55,124 By the knocking out and knocking in of different alleles of candidate genes, the favourite alleles for important traits can be identified.…”