Sex-Specific Gene Expression Ontogeny During Gonadal Development in Post-Metamorphic Xenopus tropicalis

Sexual differentiation in amphibians involves dynamic coordination between germ cells, somatic tissues, and gene expression. However, post-metamorphic gonadal maturation and sex-specific transcriptional programs underlying it remain poorly characterized. In this study, pre-pubertal gonadal development was analyzed in Xenopus tropicalis by integrating morphological, histological, and gene expression analyses. Froglets were sampled weekly from one until 8 weeks post-metamorphosis. Morphometric and histological assessments revealed progressive gonadal maturation in both sexes. In males, testicular growth correlated with body size, whereas in females, ovarian development occurred independently of somatic parameters. Expression profiling of 12 genes showed sex-specific mRNA patterns: cyp17, amh, and amhr2 displayed a male-biased expression correlated with testicular development, while aldh1a2 and ddx4 were preferentially upregulated in females and associated with ovarian growth and follicular oocyte number. Id4 declined in females but remained stable in males, reflecting, together with ddx4 expression, distinct pregametogenesis and germline maintenance strategies. Opposite regulation of aldh1a2 and cyp26b1 supported a transient meiotic wave in females versus its basal maintenance in males. Multivariate and network analyses highlighted dmrt1, amhr2, cyp17, esr1, and ddx4 as potential nodes of sex-specific regulatory networks. These findings reveal post-metamorphic, sex-specific transcriptional programs, and provide integrated molecular and histological endpoints for studies on vertebrate sex differentiation.