Advisory Committee Chair
Thane Wibbels
Advisory Committee Members
Asim Bej
Gene Hines
Douglas Watson
Douglas Weigent
Document Type
Dissertation
Date of Award
2007
Degree Name by School
Doctor of Philosophy (PhD) College of Arts and Sciences
Abstract
Temperature-dependent sex determination (TSD) is a type of environmental sex determination in which the egg’s incubation temperature determines the sex of the embryo. The exact physiology of TSD is not yet understood. Hormones and temperaturetriggered genes have been hypothesized to play a role. This study evaluates putative male and female factors that may play a role in TSD. Regarding female factors, this study evaluates clutch sensitivity to estradiol-17β and an aromatase inhibitor, and estradiol- 17β’s potential role in müllerian duct differentiation. Regarding male factors, this study also quantifies SOX9 mRNA during TSD in untreated and estradiol-17β treated embryos. In the evaluation of clutch sensitivity to estradiol-17β and fadrozole, results showed clutch sensitivity to both chemicals. Clutch sex ratios of treated eggs ranged from 100% male to 100% female and exhibited significant inter-clutch variation. The current study found that müllerian duct development is estradiol-17β sensitive. Estradiol-17β blocks development of the müllerian duct if applied before the duct’s differentiation began. If differentiation had begun, estradiol-17β caused hypertrophy in the differentiated portion, but prevented further differentiation of the müllerian duct in more caudal regions. SOX9 was chosen for the gene expression portion of the study because it is involved in testis differentiation in all vertebrates studied. Portions of turtle SOX9 were cloned in order to develop a semi-quantitative real-time PCR for examining SOX9 iii expression before, during, and after TSD. Results showed no significant difference in SOX9 expression levels between male-producing temperature and female-producing temperature during the thermosensitive period of sex determination, but a significant increase was detected after the thermosensitive period during a time when the testes were differentiating. SOX9 was also evaluated in estradiol-17β treated embryos. Embryos incubated at male-producing temperatures and treated with estradiol-17β produce females. Adrenalkidney- gonad complexes were dissected from embryos at developmental stages corresponding to SOX9 upregulation in males. Results showed a downregulation of SOX9 at stage 23, the time of testis differentiation, but showed male SOX9 levels at stage 26. This implies that estradiol-17β downregulation of SOX9 at stage 23 is sufficient for ovary formation and that SOX9 activity may be time-specific and temperature-dependent.
Recommended Citation
Dodd, Keela, "The Molecular Biology Of Temperature-Dependent Sex Determination In Reptiles" (2007). All ETDs from UAB. 3690.
https://digitalcommons.library.uab.edu/etd-collection/3690