The Role of Estrogens in Zebrafish Socio-Sexual Behaviors

Title: The Role of Estrogens in Zebrafish Socio-Sexual Behaviors
Authors: Shaw, Katherine
Date: 2023-11-20
Abstract: Sex steroids are important hormones produced in the body to regulate an individual's physiology and behavior in preparation for reproduction. Aromatase (Cyp19a1) is the steroidogenic enzyme that converts aromatizable androgens into bioactive estrogens, and hence is in a pivotal position to mediate reproductive processes and sexual behavior. In mice, evidence from whole body aromatase knockout and estrogen receptor knockout lines has revealed the critical roles of estrogen signalling in ovarian development, gonadotropin signalling, ovulation, and sexual behavior. While the ovaries have high aromatase activity levels and are a major source of circulating estrogens in the female body, they can also be locally produced in tissues via tissue-specific aromatase expression. Of particular interest, the importance of brain-derived estrogens for reproductive processes and sexual behavior is still under study. Teleosts are an amenable model system for understanding the role of brain-derived estrogens in reproduction as they have two aromatase paralogs, cyp19a1a and cyp19a1b, that are highly expressed in the ovary and brain, respectively. In this thesis, I sought to identify the importance of brain-derived estrogens for sexual behaviors and reproductive health in zebrafish using cyp19a1⁻ᐟ⁻ mutant lines and a transgenic cyp19a1b-GFP line. In dyadic sexual behavior assays, female cyp19a1b⁻ᐟ⁻ mutants took 4.1 times longer to initiate spawning behavior with wildtype (WT) males compared to WT females. This suggested a potential impairment in mate identification and assessment in the female cyp19a1b⁻ᐟ⁻ mutants. The importance of the cyp19a1 paralogs for early larval development was revealed by 4 times higher progeny mortality from cyp19a1b⁻ᐟ⁻ mutant female and cyp19a1a⁻ᐟ⁻;cyp19a1b⁻ᐟ⁻ mutant male pairings compared to WT pairings. Gene expression analyses identified significantly lower levels of important neuroendocrine genes including the estrogen receptors and the nonapeptides, arginine vasopressin (avp) and oxytocin, in the telencephalon and hypothalamus of cyp19a1b⁻ᐟ⁻ mutant female compared to WT female brains. I performed acute intraperitoneal injections of Avp and Oxytocin, as well as mixtures of their respective receptor antagonists, in cyp19a1b⁻ᐟ⁻ mutant females to determine if the behavioral impairments could be rescued in adult fish. Arginine vasopressin was found to uniquely recover the delayed oviposition in female cyp19a1b⁻ᐟ⁻ mutants. Immunohistochemistry experiments using the transgenic cyp19a1b-GFP zebrafish line with a zebrafish-validated Avp antibody revealed a close neuroanatomical proximity and contact points between radial glial cell Cyp19a1b-expressing fibres and Avp-immunopositive neurons in preoptic areas. These findings suggest that brain-derived estrogens, via Cyp19a1b activity, might affect female sexual behavior by diffusing to nearby neurons to regulate Avp signalling levels in preoptic areas. Together, these findings establish the importance of cyp19a1b for female zebrafish sexual behavior and identify a positive link between Cyp19a1b and Avp. Future study can help to characterize the estrogen-dependent pathways involved in regulating Avp signalling in the female brain and the extent of evolutionary conservation of this regulation pathway for female sexual behavior across vertebrates.
CollectionThèses, 2011 - // Theses, 2011 -