Degree Type

Thesis

Date of Award

2020

Degree Name

Doctor of Philosophy

Department

Ecology, Evolution, and Organismal Biology

Major

Genetics and Genomics

First Advisor

Nicole N Valenzuela

Abstract

Sex determination is a biological process that decides the sexual fate of an organism. Sex determining mechanisms can range between two extremes: genotypic sex determination (GSD) and environmental sex determination (ESD). In most turtle species, sex is determined by the environment, being temperature the most common factor in a process called temperature-dependent sex determination, a textbook example of phenotypic plasticity. However, sexual development is not only affected by temperature, but it is also susceptible to contaminants that can alter the endocrine system, influencing the sex fate directly.This dissertation investigated the effects of temperature and contaminants on DNA methylation, an epigenetic mechanism that directly influences gene expression of regulators of sexual development. In Chapter 1, I reviewed the literature to provide an overview of current knowledge of how endocrine disrupting compounds (EDCs) affect genetic and hormonal processes in sex determination. In Chapter 2, I examined the gene Dmrt1, which is necessary for vertebrate male sexual development, in the painted turtle Chrysemys picta. I identified and characterized a novel Dmrt1 isoform and profiled the expression of the canonical and novel Dmrt1 transcripts during embryonic development of C. picta. In Chapter 3, I tested the application of a method that combines DNA digestion by methylation-sensitive restriction enzymes and PCR to assess the methylation status of genes of interest. For this, I analyzed high-throughput data from a hybrid methylome sequencing method that combines immunoprecipitation (MeDIP) and bisulfite conversion of methylated DNA, in order to identify differentially methylated regions in the tail tissue of C. picta that could be used as a molecular marker for sex diagnosis of TSD turtles. In Chapter 4, I analyzed embryonic methylomes of C. picta from stages before, at the onset of, and late in the thermosensitive period for sex determination, to explore when the DNA methylation patterns observed in hatchling gonads in previous studies are established during development, and whether DNA methylation profiles are affected by temperature in ways likely to drive differential transcription of the sexual development genetic network (by comparing DNA methylation to matched transcriptomic data). This chapter replaced my original project to investigate the effects of cadmium (an ecotoxin) on DNA methylation of two sexual development genes, Dmrt1 and aromatase during embryonic development, which was disrupted by the COVID-19 pandemic. Together, these chapters enlighten the effects of environmental factors, specially temperature, on the genetic and epigenetic architecture of sex determination, and advances our understanding of the challenges that environmental disturbance from climate change and pollution might pose to natural population of turtles

DOI

https://doi.org/10.31274/etd-20210114-95

Copyright Owner

Beatriz Akemi Mizoguchi

Language

en

File Format

application/pdf

File Size

148 pages

Available for download on Friday, January 07, 2022

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