FOXL3 (forkhead box L3) is a transcriptional regulator that functions as a germ cell-intrinsic determinant of sexual fate in vertebrates, particularly in teleost fish 1. As a DNA-binding transcription factor specific to RNA polymerase II, FOXL3 plays a critical role in gonadal sex differentiation through evolutionarily conserved mechanisms 2. In testicular development, FOXL3 operates within the AR-foxl3-rec8/fbxo47 signaling axis, where androgens enhance FOXL3 promoter activity, enabling FOXL3 to upregulate meiotic genes rec8 and fbxo47 that facilitate spermatogenesis 3. Expression patterns indicate FOXL3 is predominantly expressed in male germ cells, whereas its paralog FOXL2 specializes in ovarian somatic cells, representing subfunctionalization following gene duplication 2. FOXL3 expression is tightly regulated by miRNA suppression and is sensitive to endocrine disruption; environmental exposure to pharmaceutical mixtures increases FOXL3 mRNA levels approximately 5-fold, affecting germ cell fate determination 4. Loss-of-function studies demonstrate that FOXL3-established germ cell sexual identity enables proper gametogenesis independently of surrounding somatic cell sex 1. This makes FOXL3 essential for the cell-autonomous determination of germline sexual identity distinct from other gametogenic pathways.