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RISS 인기검색어
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- 저자 : Kossack, Michelle E (검색결과 1 건)
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Kossack, Michelle E University of California, Davis ProQuest Dissertat 2019 해외박사(DDOD)
Passing on genetic information from one generation to another through sexual reproduction hinges on the successful process of sex determination. Sex determination, or the process of becoming female or male, is a balance of male and female specific pathways. By better understanding these pathways I hope to strengthen the use of zebrafish as a model for reproductive toxicology.Over the last several decades, zebrafish (Danio rerio) have become a major model organism for the study of vertebrate development and physiology. Given this, it may be surprising how little is known about the mechanism by which sex is determined in zebrafish. While zebrafish are a gonochoristic species (having two sexes) that do not switch sex as adults, it was appreciated early on that sex ratios obtained from breeding lab domesticated lines were not typically a 1-to-1 ratio of male to female which suggests that sex is not determined solely by a chromosomal mechanism. In chapter 1, I review what is known about the recent progress towards defining the genetic mechanism for sex determination in both wild and domesticated zebrafish.In mammals, WNT4 is a signaling ligand that is essential for ovary and Mullerian duct development, where it antagonizes the male-promoting FGF9 signal. Wnt4 is well conserved across all vertebrates, but it is not known if Wnt4 plays a role in sex determination and/or the differentiation of sex organs in non-mammalian vertebrates. This question is especially interesting in teleosts, such as zebrafish, because they lack an Fgf9 ortholog. In chapter 2, I show that wnt4a is the ortholog of mammalian Wnt4, and that wnt4b in teleosts was present in the last common ancestor of humans and zebrafish but was lost in mammals. I show that wnt4a loss-of-function mutants develop predominantly as males and conclude that wnt4a activity promotes female sex determination and/or differentiation in zebrafish. Additionally, both male and female wnt4a mutants are sterile due to defects in reproductive duct development.It had been previously characterized that Amh signaling is critical for normal gonad function in mammals and zebrafish. In mammals AMHR2 is the TGF-棺 type 2 receptor known to activate AMH signaling. However, zebrafish do not have an amhr2 gene in their genome. It was previously identified that two TGF-棺 type 2 receptors, bmpr2a and bmpr2b, are expressed in the follicle layer in zebrafish ovaries. Using CRISPR/Cas9, I created null alleles for bmpr2a and bmpr2b. In chapter 3, I show that bmpr2a mutant males develop hypertrophic gonads that overaccumulate early stage germ cells consistent with previously described amh and bmpr1bb mutants. bmpr2a mutant females are initially normal. However, they slowly accumulate early stage oocytes by 6 months post fertilization, similar to amh and bmpr1bb mutants. bmpr2b mutant males have no obvious gonad defect, yet bmpr2b mutant females are unable to mature their oocytes beyond stage III similar to bmp15 mutants. Finally, I found that double bmpr2a.
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