Abstract
Simple SummaryMisgurnus anguillicaudatus not only exhibits sexual size dimorphism, but also shows polyploid size dimorphism. Here, we performed comparative transcriptome integration analysis of multiple tissues of diploid and tetraploid M. anguillicaudatus of both sexes. We found that differences in energy metabolism and steroid hormone synthesis levels may be the main causes of sexual and polyploidy growth dimorphisms of M. anguillicaudatus. Fast-growing M. anguillicaudatus (tetraploids, females) have higher levels of energy metabolism and lower steroid hormone synthesis and fatty acid degradation abilities than slow-growing M. anguillicaudatus (diploids, males).Sexual and polyploidy size dimorphisms are widespread phenomena in fish, but the molecular mechanisms remain unclear. Loach (Misgurnus anguillicaudatus) displays both sexual and polyploid growth dimorphism phenomena, and are therefore ideal models to study these two phenomena. In this study, RNA-seq was used for the first time to explore the differentially expressed genes (DEGs) between both sexes of diploid and tetraploid loaches in four tissues (brain, gonad, liver, and muscle). Results showed that 21,003, 17, and 1 DEGs were identified in gonad, liver, and muscle tissues, respectively, between females and males in both diploids and tetraploids. Regarding the ploidy levels, 4956, 1496, 2187, and 1726 DEGs were identified in the brain, gonad, liver, and muscle tissues, respectively, between tetraploids and diploids of the same sex. When both sexual and polyploid size dimorphisms were considered simultaneously in the four tissues, only 424 DEGs were found in the gonads, indicating that these gonadal DEGs may play an important regulatory role in regulating sexual and polyploid size dimorphisms. Regardless of the sex or ploidy comparison, the significant DEGs involved in glycolysis/gluconeogenesis and oxidative phosphorylation pathways were upregulated in faster-growing individuals, while steroid hormone biosynthesis-related genes and fatty acid degradation and elongation-related genes were downregulated. This suggests that fast-growing loaches (tetraploids, females) have higher energy metabolism levels and lower steroid hormone synthesis and fatty acid degradation abilities than slow-growing loaches (diploids, males). Our findings provide an archive for future systematic research on fish sexual and polyploid dimorphisms.
Highlights
Sexual size dimorphism, which is the relative difference in body size and growth rate between males and females of the same species, has been observed in many cultivable fish species, and this phenomenon varies widely across species
After using the Trinity software, de novo sequence assembly resulted in 351,696 unigenes with 956 bp N50 and an average length of 791 bp ranging from 301 bp to 42,939 bp (Tables S3 and S4)
A heat-map was constructed by filtering some key genes related to glycolysis and oxidative phosphorylation pathways, and the results showed that genes related to glycolysis had high expression levels in both diploid and tetraploid muscle tissues, while most of the genes related to oxidative phosphorylation had high expression levels in multiple tissues (Figure 6)
Summary
Sexual size dimorphism, which is the relative difference in body size and growth rate between males and females of the same species, has been observed in many cultivable fish species, and this phenomenon varies widely across species. RNA-Seq has been used to identify sex-biased genes in many fish species, such as platy fish (Xiphophorus maculatus) [9], O. mykiss [10], O. niloticus [11], rockfish (Sebastiscus marmoratus) [12], catfish (Ictalurus punctatus) [13], and turbot (Scophthalmus maximus) [14]. Such studies have provided some overview of sex-biased gene expression in fish and offer more useful information about sexual dimorphism
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