Microglia and Chek2 contribute to sex-specific organization of the adult zebrafish brain

Sex specific differences in size and distribution of cell types have been observed in mammalian brains. How sex-specific differences in the brain are established and to what extent sexual dimorphism contributes to sex-biased neurodevelopment and neurological disorders is not well understood. Microglia are the resident immune cells of the nervous system and have been implicated in masculinizing the mammalian brain and refining neural connections to promote remodeling of neural circuitry, yet their contributions to developmental brain patterning and plasticity in zebrafish remains unclear. Here, we report anatomical and cellular differences between juvenile brains and adult female and male brains. Leveraging the plasticity of the zebrafish female brain and genetic models lacking microglia and tumor suppressor factors, we provide insight into the mechanisms that establish sex-specific brain dimorphism in zebrafish. Specifically, we identified sexually dimorphic features in the adult zebrafish brain that depend on microglia and Chek2, which may have broader implications and represent therapeutic targets for sex-biased neurological disorders. Plain language summaryMales and females of species can have significant differences in appearance, including differences in size, color, or sex specific anatomical structures. In addition to overt morphological differences, sex specific differences in size and distribution of cell types have been observed in mammalian brains. How these sex-specific differences in the brain are established and to what extent these differences contribute to sex-specific neurodevelopment and neurological disorders that differentially impact males and females is not well understood. Despite an incomplete picture of the mechanisms regulating sex-specific development, some of the cell types involved include microglia. Microglia are the resident immune cells of the nervous system and have been implicated in promoting features that are typical in the male mammalian brain. Specifically, microglia may refine neural connections and promote remodeling of neural circuitry and influence sex-specific behaviors. The contributions of microglia to developmental brain patterning and plasticity in zebrafish remain unclear. Here, we report anatomical and cellular differences between juvenile brains and adult female and male brains. Leveraging zebrafish genetic models lacking microglia and tumor suppressor factors, and the unique plasticity of the zebrafish female brain, we investigated and provide insight into the mechanisms that establish sex-specific brain differences in zebrafish. Specifically, we identified sexually distinct features in the adult zebrafish brain that depend on microglia and the tumor suppressor Chek2. If these or similar mechanisms operate in other species, our findings may have broader implications for sex-specific brain development and represent therapeutic targets for sex-biased neurological disorders. HighlightsO_LITissue clearing and immunostaining of juvenile and adult whole-mount zebrafish brains allows analysis of sex differences. C_LIO_LIAnatomical and cellular sexual dimorphism in the adult vertebrate brain appears after gonadal sex differentiation. C_LIO_LISexual dimorphism in the adult brain is driven by differences in cell death regulation. C_LIO_LIMicroglia colonization of brain areas involved in courtship is sexually dimorphic. C_LIO_LIMicroglia involvement in establishing sex-specific differences in the adult brain. C_LI