Neural and molecular control of subordinate social status in a cichlid fish

PROJECT SUMMARY/ABSTRACT Social stability for many species is maintained via social hierarchies, wherein displaying subordinate behavior to higher ranking individuals is key. A subordinate social rank influences the brain and behavior by altering neural circuitry and the production and signaling of neuromodulators, such as steroid hormones and neurotransmitters. For example, androgens tend to be negatively correlated with a subordinate social rank, while the neural expression of the serotonin 1A (5-HT1A) receptor is positively associated with subordinate behavior. Although clear relationships have been established between a subordinate social status, the brain, and behavior, the molecular and neural mechanisms regulating these changes are not known. A major challenge in elucidating these mechanisms is that social rank is often tied to both physiological and behavioral traits, making it difficult to distinguish the effects of neuromodulators (e.g., androgens and serotonin) on individual traits associated with social subordination. Thus, the use of novel model organisms, in which distinct traits of subordinate social status can be studied in isolation, is necessary to enhance our understanding of the neuroendocrine regulation of subordination. The proposed work will use state-of-the-art sequencing and genome editing technologies to identify genes and cell types in the brain that govern subordinate social status in the African cichlid fish Astatotilapia burtoni. A. burtoni is a highly social species in which males display subordinate or dominant behavior based on social status. Recent work showed that androgen receptor (AR) mutant males generated via CRISPR/Cas9 gene editing do not exhibit distinct traits of dominant social rank. For example, ARα mutants do not perform dominant behaviors (mating or aggression), whereas ARβ mutants lack bright coloration and show reduced testes growth, making these fish an excellent tool for taxing the molecular and neural systems controlling distinct aspects of subordinate social status. In Specific Aim 1, I will identify cell types and their genetic signatures in the hypothalamus of dominant WT males and subordinate WT and AR mutant males using single-nucleus RNA sequencing. In Specific Aim 2, I will determine the role of androgens in regulating subordinate social status by measuring physiological and behavioral traits of social rank in subordinate AR mutants. Finally, in Specific Aim 3, I will generate novel mutant A. burtoni lacking the 5-HT1Aβ receptor using CRISPR/Cas9 gene editing to assess the role of serotoninergic signaling in governing social subordination. Based on preliminary data showing that AR and AR mutants display distinct physiological responses to social suppression, I predict these mutants will have cell type-specific gene expression patterns that mirror different aspects of subordination. Moreover, given the known relationship between androgen and serotoninergic signaling, I expect to observe contrasting deficits in physiological and behavioral traits of subordination in AR and 5-HT1Aβ mutants that reveal the roles of these systems in controlling subordinate social status. Collectively, these studies will yield important insights into the basic neural and molecular mechanisms that regulate subordination in social animals, including humans.