Abstract
Simple SummaryThe fate of the gonad in teleost is influenced by various factors, including genetics and external factors. Several species-specific genes and environmental factors involved in sex determination and differentiation have been identified in teleost. In addition, these factors are species-specific. At the brain level, suppression of key molecule of the hypothalamus–gonadal axis affects sex determination. At the same time, pituitary hormones are required for regulating sex differentiation. However, the role of the brain during sex determination and differentiation remains elusive. In this review, we have gathered and discussed the findings on the role of prominent genes, environmental factors, and the brain in regulating sex determination and differentiation of teleost. The fish reproductive system is a complex biological system. Nonetheless, reproductive organ development is conserved, which starts with sex determination and then sex differentiation. The sex of a teleost is determined and differentiated from bipotential primordium by genetics, environmental factors, or both. These two processes are species-specific. There are several prominent genes and environmental factors involved during sex determination and differentiation. At the cellular level, most of the sex-determining genes suppress the female pathway. For environmental factors, there are temperature, density, hypoxia, pH, and social interaction. Once the sexual fate is determined, sex differentiation takes over the gonadal developmental process. Environmental factors involve activation and suppression of various male and female pathways depending on the sexual fate. Alongside these factors, the role of the brain during sex determination and differentiation remains elusive. Nonetheless, GnRH III knockout has promoted a male sex-biased population, which shows brain involvement during sex determination. During sex differentiation, LH and FSH might not affect the gonadal differentiation, but are required for regulating sex differentiation. This review discusses the role of prominent genes, environmental factors, and the brain in sex determination and differentiation across a few teleost species.
Highlights
Teleost have the most diverse reproductive system and reproductive strategies among vertebrate species
Teleost is an exciting group of organisms to investigate the evolution of sex determination and sex differentiation due to their vast range of reproductive systems, from hermaphrodites to gonochoristic and plasticity of adult sex change [1]
As the Müllerian duct is absent in teleost [44], Amhy protein regulates the expression of foxl2 and cyp19a1a mRNAs [45] and plays a critical role as a sex determination gene in male fishes. amhy was discovered as a sex determination gene in the Patagonian pejerrey (Odontestes hatcheri) [46] and, more recently, in the Nile tilapia [5], cobaltcap silverside [33], Northern pike [34], and rockfish [35]
Summary
Teleost have the most diverse reproductive system and reproductive strategies among vertebrate species. As the Müllerian duct is absent in teleost [44], Amhy protein regulates the expression of foxl and cyp19a1a mRNAs [45] and plays a critical role as a sex determination gene in male fishes. Dmy, known as dmrt1by gene, is a male sex-determining gene in Japanese medaka This gene is identified as a duplicate of the autosomal dmrt gene found in the sex-determining region of the Y-chromosome. Besides the Philippine medaka, the autosomal gsdf gene (chromosome 6) has been classified as a sex determination gene in the rainbow trout [9]. To generate a novel Y chromosome, the sox3Y gene can be independently recruited where sox can activate downstream gsdf gene (a critical factor in fish male differentiation pathway) function [59]. Few reports in the teleost indicate sox3Y as a master sex-determining gene, further studies are needed across the species to conclude sox3Y as a significant player
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