Date of Award

8-2021

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology/Molecular, Cellular, and Organismal Biology

First Advisor

Kellee R. Siegfried

Second Advisor

Alexey Veraksa

Third Advisor

Catherine McCusker

Abstract

The dmrt gene family is ancient and highly conserved, with roles in sex determination and differentiation, in addition to other developmental processes. In domesticated zebrafish, sex determination is polygenic, making identification of underlying mechanisms that regulate sex difficult. My thesis aims to parse the roles of the dmrt gene family in zebrafish sex determination and differentiation. The zebrafish dmrt1 gene was previously shown to be critical for normal male development, so to better understand how dmrt1 functions in the gonad, we developed and analyzed transgenic zebrafish expressing dmrt1 specifically in the germ cells and in gonadal somatic cells. We found that dmrt1 expression in germ cells, but not in gonadal somatic cells, is sufficient to partially rescue the dmrt1-/- phenotype, and that overexpression of dmrt1 in germ cells causes male-biased populations. Thus, over-expression of dmrt1 in germ cells can drive male fate. The dmrt1 mutants are heavily female biased, however a small percentage of mutants develop as sterile males, thus male fate can be specified independently of dmrt1. We posit that other members of the dmrt gene family act redundantly with dmrt1 to determine male sexual fate. Zebrafish have five dmrt genes: dmrt1, dmrt2a, dmrt2b, dmrt3, and dmrt5, which all exhibit expression in both male and female gonads. We characterized mutations disrupting dmrt2a/2b/3/5 to identify any roles in gonad development. We found that while dmrt2a and dmrt5 homozygous mutants were nonviable, dmrt3 and dmrt2b mutants were homozygous adult viable. Loss of dmrt2b did not affect family sex ratios, gonad histology, or fertility indicating that this gene does not have necessary roles in sexual development, whereas dmrt3 loss produced only minor effects on male fate. To ask if dmrt2a/2b/3 synergize with dmrt1, we analyzed double mutants. Interestingly, dmrt2a mutations were partially viable when double-mutant with dmrt1. Data for dmrt1;dmrt2a mutants suggest that loss of dmrt2a biased fish towards a male fate. Furthermore, double mutants for dmrt1;dmrt2a or dmrt1;dmrt3 exhibited defects in ovary development and misexpression of genes involved in sexual development. Overall, my data demonstrates that dmrt1 drives male fate whereas dmrt2a and dmrt3 have roles in female sexual development.

Comments

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