Pingrui Xu

Sex determination and gonadal differentiation are essential for vertebrate development and reproduction. Fish, with both genetic and environmental sex-determining mechanisms, serve as ideal models for exploring environmental effects on gonadal development. The hypothalamic–pituitary–gonadal (HPG) axis is involved in sex differentiation, but its role as a key mediator in temperature-dependent sex differentiation remains unclear. Sebastes schlegelii is an economically important marine fish species along the northern coast of China. It exhibits obvious sexual growth dimorphism and typical temperature-dependent sex differentiation, making it an excellent model for investigating the mechanism of sex differentiation. In this study, individuals of S. schlegelii at the sex differentiation stage were treated with a GnRH receptor antagonist and subjected to transcriptome sequencing analysis. The results revealed that GnRH may regulate sex differentiation through steroid biosynthesis, TGF-β and MAPK signaling pathways. We identified several key genes, including srd5, bmp8a, bmp2, fgf23, pdgfra, and egfr, which may affect gonadal differentiation by acting on core sex-determining genes and steroidogenesis. In conclusion, GnRH precisely mediates the process of sex differentiation by modulating the TGF-β signaling pathway, the MAPK signaling pathway, and local gonadal steroidogenic networks.

The fish species Oplegnathus fasciatus exhibits an X₁X₁X₂X₂/X₁X₂Y sex determination mechanism. This species holds considerable economic value and displays pronounced sexual dimorphism in growth. Therefore, the development of a rapid and accurate method for sex identification is critical to enhancing breeding efficiency and maximizing production value. Using third-generation PacBio whole-genome sequencing, we identified a homologous region in the samd3/elf3 intergenic region of the X and Y chromosomes of O. fasciatus. Analysis of the whole-genome sequence revealed a large DNA insertion marker fragment within this region. Using specifically designed primers, two bands of 390 bp and 1008 bp were successfully amplified in males, whereas only a single 390 bp band was detected in females. This marker can be easily distinguished by agarose gel electrophoresis, greatly enhancing the efficiency and accuracy of sex identification. This study not only expands the molecular marker system for sex identification of O. fasciatus but also offers a valuable methodological reference for sex identification in other economically important fish species. These findings have significant implications for germplasm improvement and efficient selection in aquaculture.

Spotted knifejaw (Oplegnathus punctatus) is an economically important marine cultured species exhibiting a unique complex sex chromosome system (X₁X₁X₂X₂ in females and X₁X₂Y in males), with males possessing one fewer chromosome (2n = 47) than females (2n = 48) and an abnormally large Y chromosome. Additionally, males demonstrate significant growth advantages over females. Rapid and accurate sex identification is essential for effective culture management, selective breeding, and population control. In this study, we identified a homologous region of the tmem88 gene containing large DNA insertion markers on the X and Y chromosomes through whole-genome sequencing of O. punctatus. The X₁ chromosome harbors a 278 bp DNA fragment, whereas the Y chromosome contains a 1472 bp fragment, resulting in a 1194 bp size difference indicative of structural variation in the non-coding region of the tmem88 gene. We developed a rapid detection method based on this variation, utilizing a pair of primers that amplify two distinct bands (278 bp and 1472 bp) in male (X₁X₂Y) individuals and a single 278 bp band in female (X₁X₁X₂X₂) individuals when analyzed by agarose gel electrophoresis. This method enables efficient and accurate sex differentiation in O. punctatus, significantly reducing the time required for identification and enhancing detection efficiency. This study provides a valuable tool for the rapid identification of sex in O. punctatus, facilitating improved breeding strategies and supporting the large-scale production of high-quality fry.

Spotted knifejaw (Oplegnathus punctatus), one of the most valuable mariculture species, grows with significant sexual dimorphism, with males growing significantly faster than females. O. punctatus not only has excellent growth characteristics and high food value, but also shows high economic value in aquaculture, which has become a hotspot in the field of aquaculture. The current insufficiency of sex marker identification in O. punctatus restricts the process of its unisexual breeding. Rapid identification of sex will help to study the mechanisms of sex determination and accelerate the development of sex-controlled breeding. With the completion of the sequencing of the male and female genomes of O. punctatus, the efficient and precise development of genetic sex markers has been made possible. In this study, we used genome-wide information combined with molecular biology techniques from marker sequences to further establish a rapid method for DNA insertion variant detection in the intron of O. punctatus erc2 gene, which can be used to rapidly, accurately, and efficiently identify whether DNA insertion occurs in the intron of O. punctatus erc2 gene to be detected, and to identify the sex of O. punctatus to be detected. It could also be distinguished by agarose gel electrophoresis, which would shorten the time for accurate identification and improves the detection efficiency. Homozygous comparison of male and female individuals showed that the length of the DNA fragment of the erc2 gene was 239 bp on chromosome X₁ and 1173 bp on chromosome Y. It can therefore be inferred that a 934 bp insertion fragment exists on the Y chromosome. The PCR amplification results showed that two DNA fragments of 1173 bp and 239 bp could be amplified in male O. punctatus, and the 1173 bp fragment was a marker fragment specific to the variant intron erc2 gene, while only a single DNA fragment of 239 bp was amplified in female O. punctatus. It has important significance and application value in the study of neurotransmitter transmission and environmental adaptability of female and male fish based on erc2 gene, as well as the identification of male and female sex, the preparation of high male fry, and family breeding.