International Journal of Aquaculture, 2025, Vol.15, No.4, 184-196 http://www.aquapublisher.com/index.php/ija 186 the study observed that the gene expression of pituitary FSH and gonadal FSHR was gradually increased; experimental injection of recombinant FSH protein can successfully induce gender reversal of mature female fish. This finding suggests that the gonadotropin-sex hormone axis is one of the key endocrine pathways in grouper gender conversion. 3 Gender Determines Key Genes and Their Expression Patterns 3.1 Identification and expression of key genes related to male and female 3.1.1 The role of dmrt family genes in male decisions The Dmrt1 gene (Doublesex and Mab-3 Related Transcription factor 1) is widely regarded as one of the core decision makers in the gender pathway of vertebrate males, serving as a “testicle determinant” or semen maintenance factor in many species (Augstenová and Ma, 2024). Fish such as grouper do not have the Sry gene on the Y chromosome like mammals, but the high expression of dmrt1 in most fish males suggests its important position in gender decisions. For example, in Nile tilapia, dmrt1 is one of the most expressed genes in the testicles during the gender differentiation stage; gene editing causes Dmrt1 function to be depleted, which will lead to severe testicular dysplasia in XY males, degeneration and disappearance of spermatogonia in the semen, support cells mistakenly transform into follicle cells, and abnormal activation of female pathway genes such as Foxl2 and cyp19a1a. Recent grouper transcriptome analysis further confirmed that dmrt1 was significantly upregulated early in the process of gender reversal, consistent with androgen-induced testicular development. In addition to Dmrt1, other members of the Dmrt gene family such as dmrt2 and dmrt3 have also been reported to be involved in gonadal development in different species, but their effects are mostly indirect or auxiliary (Zhang et al., 2020). Several DMRT family genes have also been identified in the grouper genome, but their functions need further research. 3.1.2 The relationship between Foxl2 and female maintenance Foxl2 is one of the important transcription factors that maintain ovarian fate and oocyte survival. In mammals, the sustained expression of Foxl2 is essential for inhibiting male genes and maintaining the ovarian phenotype; in fish, Foxl2 is also considered a marker gene for the female pathway (Fan et al., 2019). In most female individuals such as grouper, Foxl2 is expressed at high levels in ovarian tissue, while in male sprites, which are extremely low in male sprites. Foxl2 mainly enhances estrogen synthesis by promoting the transcription of the aromatase cyp19a1a, thereby supporting ovarian development. During the gender reversal of grouper, the expression dynamics of Foxl2 also echo the process of the transition from the ovary to the sperm: Foxl2 was rapidly downregulated in the early stage of sexual reversal, while male factors such as dmrt1 and amh were upregulated, marking that the "switch" of molecular regulation was switched from female mode to male mode (Lyu et al., 2019). It is worth noting that in recent years, an ancient paralogous gene of Foxl2, foxl3, has also been found in fish. Its function is both similar and antagonistic to Foxl2. In orange-spot grouper, Foxl3 was shown to directly inhibit the expression of cyp19a1a, thereby promoting schizophrenia differentiation; while Foxl2 promoted cyp19a1a to maintain the ovary. 3.1.3 Synergistic mechanism of bidirectional regulation of genes In the molecular network of grouper gender determination, some key factors do not promote a certain gender in one direction, but work together in an antagonistic pairwise manner to form a steady-state "bistable" switch. This mechanism is widely present in vertebrate gender decisions. For example, Dmrt1 and Foxl2 form a mutual inhibitory network between the male pathway and the female pathway: Dmrt1 not only activates male genes in the testicles, but also prevents the activation of ovarian genes by inhibiting the expression of Foxl2; accordingly, in addition to upregulating estrogen synthetase in the ovary, Foxl2 also inhibits the expression of male-related genes (including Dmrt1) and prevents the initiation of male programs. This mutual suppression of each other's "competition" ensures that the gonads differentiate in a single direction. Once a side has the advantage, it will further consolidate itself and inhibit the other party through positive feedback, thereby maintaining the gender stability of the gonads. However, in hermaphrodites such as grouper, the equilibrium can be broken under certain conditions, causing the otherwise stable ovarian state to turn to the genital state. This often involves the interference of external signals on the "two-way regulatory gene" network. For example, when environmental or
RkJQdWJsaXNoZXIy MjQ4ODYzNA==