Vitellogenin (Vtg) is a precursor to yolk-proteins produced in the liver of many invertebrates and non-mammalian vertebrates; its synthesis is stimulated by the hormone estradiol (E2). This study is the first to characterize vitellogenin synthesis in a placental viviparous elasmobranch, the yolk-sac placental bonnethead shark, Sphyrna tiburo. This study focused on determining where and when Vtg is produced, as well as what hormonal factors regulate Vtg production. The liver was confirmed as the site of Vtg production via immunohistochemistry. Immunoreactivity was also observed within granulosa cells of ovarian follicles; further experimentation is needed to determine if this is indicative of Vtg production by these cells. Using immunoblotting, the highest proportions of Vtg positive females were found in March, with Vtg production continuing into April and May. Putative Vtg production was found to begin in August for some individuals, with production continuing throughout the fall and winter months. In regards to hormonal regulation, immunohistochemical analysis identified receptors for E2 and progesterone (P4) within the liver. Comparison of the monthly E2 and Vtg cycles provides evidence that E2 stimulates Vtg production in S. tiburo, as high or increasing concentrations of E2 correlated with Vtg presence in the plasma. Preliminary results also suggest in vitro production of Vtg by liver tissue when exposed to E2. Comparison of the monthly P4 and Vtg cycles suggests P4 may inhibit Vtg synthesis, with higher levels of P4 found in the months when Vtg production declines. Additionally, the methods developed for this study were able to identify Vtg in the plasma of other elasmobranch species. Vtg detection in plasma may thus be an ideal new, nonlethal method for characterizing elasmobranch reproductive periodicity, which will aid in assessing population growth and allow for managers to possess more accurate information to make appropriate decisions for the populations.
| Identifer | oai:union.ndltd.org:unf.edu/oai:digitalcommons.unf.edu:etd-1868 |
| Date | 01 January 2018 |
| Creators | Mowle, Adrien Kathleen |
| Publisher | UNF Digital Commons |
| Source Sets | University of North Florida |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | UNF Graduate Theses and Dissertations |
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