Sex determination is a key developmental process in several species regulated by sexrelated
transcription factors. In many species a gene called doublesex and mab-3 related
transcription factor 1 (dmrt1), plays an important role in sexual differentiation. I used African
clawed frogs (Xenopus) to examine function of dmrt1 in two species: a diploid species, X.
tropicalis, and an allotetraploid species, X. laevis. In both species, dmrt1 is an autosomal gene;
Xenopus tropicalis has one copy of dmrt1 and X. laevis has two homeologous copies that by
definition are derived from whole genome duplication: dmrt1.L and dmrt1.S in X. laevis. We
generated knockouts of each of these genes to further examine their function in sexual
differentiation. Histological examination showed testicular dysgenesis in X. tropicalis dmrt1 and
X. laevis dmrt1.L null males whereas dmrt1.S null males presented no obvious difference in
sperm density compared to wildtype males. X. tropicalis dmrt1 and X. laevis dmrt1.L null
females were found to completely lack reproductive organs and are infertile whereas dmrt1.S
null females appeared unaffected. The contrasting results between dmrt1.L and dmrt1.S in X.
laevis provides evidence of both neofunctionalization and subfunctionalization following gene
duplication and suggest that gene duplication is a major contributor to evolutionary change.
Additional investigation of the transcriptome of these frogs and the role of dmrt1 in the
secondary sex characteristic vocalization provides further evidence of the role of dmrt1 in
development. Comprehensively, this investigation provides further knowledge of the role of
dmrt1 and homeologs of this gene in sexual differentiation and introduces a novel aspect of this
gene in female development. Future efforts are focused on generating double knockouts for
dmrt1.L and dmrt1.S, further examining the role of dmrt1.S in somatic cell function and
developing additional mutant lines in other Xenopus for comparative analysis. / Thesis / Master of Science (MSc) / In many species sexual differentiation is a crucial developmental event. Surprisingly,
however, the systems orchestrating sexual differentiation are highly variable among species. The
doublesex and mab-3 related transcription factor 1 (dmrt1) gene plays a role in sexual
differentiation in many groups, but its specific roles in this process are incompletely
characterized and potentially diverse. We used genetic engineering in two species of African
clawed frog (Xenopus) to disable function of dmrt1 in order to explore effects on gonadal
development and the development of secondary sex characteristics. We found that dmrt1 is
required for normal ovary or testis development in both Xenopus species, and that functional
divergence occurred following duplication of dmrt1 by whole genome duplication. Taken
together, these findings identify previously uncharacterized roles of dmrt1 in Xenopus and
provide evidence of dynamic functional evolution of this important gene.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/28873 |
| Date | 11 1900 |
| Creators | Kukoly, Lindsey |
| Contributors | Evans, Ben, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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