Influence of Insulin, Insulin-Like Growth Factor I and Sex Steroids On the Regulation of the Vitellogenin Receptor In Developing Oocytes of Largemouth Bass (Micropterus Salmoides)

<p> Fish vitellogenin synthesized and released from the liver of oviparous animals is taken up into oocytes by the vitellogenin receptor (<italic>vtgr</italic>). This is an essential process in providing nutrient yolk to developing embryos to ensure successful reproduction. Here we disclose the LMB <italic>vtgr</italic> cDNA sequence that shares high homology with other fish species and conserved domains that classify it as a member of the low density lipoprotein receptor (LDLR) superfamily. The overarching goals of this research were to begin to characterize the expression of LMB <italic>vtgr</italic> in ovarian tissues during normal reproduction, determine the role of hormones in regulating this gene at the transcriptional level and discern the ability of select environmental chemicals to interfere with pathways that control <italic>vtgr</italic>expression. </p> <p> During the normal reproductive cycle we discovered that <italic>vtgr</italic> was most highly expressed in ovarian tissues containing oocytes in primary stages of growth which correlated with patterns observed for estrogen receptor (<italic>esr</italic>) subtypes, androgen receptor (<italic>ar</italic>) and insulin-like growth factor-1 (<italic>igf1</italic>). Using <italic>ex vivo</italic> experiments it was determined that both Insulin and IGF1 induce the expression of <italic>vtgr</italic> in ovarian follicles in early growth stages. Preliminary studies suggest involvement of MAPK signaling in IGF1 driven <italic>vtgr</italic> expression. </p> <p>Interestingly, while both E₂ and 11-KT singly had no effect on <italic>vtgr</italic> mRNA levels, they were able to suppress INS-induced <italic>vtgr</italic> mRNA levels. Identification of the first vertebrate <italic>vtgr</italic> promoter revealed a number of DNA motifs that are potential targets of hormone pathways including GATA-1 and ERE, among others. Functional promoter analysis studies revealed a primary role for <italic>esr1</italic> and <italic>esr2a</italic> in repressing <italic>vtgr</italic> transcription. The involvement of E₂ in downregulation of <italic>vtgr</italic> mRNA was confirmed in ovarian tissues of LMB exposed <italic>in vivo</italic>. Finally, the xenoestrogen 17á-ethinyl estradiol (EE₂), but not bisphenol-A (BPA), was able to modulate promoter activity via Esrs and repress <italic>vtgr</italic> expression <italic>in vivo</italic> in a manner similar to E₂. These results provide for the first time evidence for the ordered stage-specific expression of LMB <italic>vtgr</italic> during the normal reproductive process and the complex interactions between Ins, Igf and E₂ signaling pathways. Furthermore, we identify the <italic>vtgr</italic> as a potential target of xenoestrogens which brings to light the involvement of this gene in effects imparted by these chemicals.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Campus Access Dissertation

Discipline thesis:degree_discipline

Environmental Health Sciences

Year

2012

Author dc:creator

• Dominguez, Gustavo

Contributors dc:contributor

• David C Volz
• Tara L Sabo-Attwood

• Environmental Health
• Environmental Sciences
• Life Sciences
• Pharmacology, Toxicology and Environmental Health
• Physical Sciences and Mathematics
• estrogen receptor
• insulin
• insulin-like growth factor
• largemouth bass
• oocyte
• vitellogenin receptor

Statement dc:rights

• © 2012, Gustavo Dominguez

Repository record dc:identifier

https://scholarcommons.sc.edu/etd/1120

OAI identifier oai:identifier

oai:scholarcommons.sc.edu:etd-2121