Sertoli cells provide nutrients and growth factors for developing germ cells. Each Sertoli cell can support a finite number of developing germ cells. During development of the testis, cessation of Sertoli cell proliferation and the onset of differentiation establishes the final number of Sertoli cells and hence the number of sperm that can be produced. Studies in this dissertation explore the hypothesis that the transition from proliferation to differentiation is facilitated by E-box transcription factors that induce the expression of differentiation-promoting genes. The relative activities of E-box proteins were studied in primary Sertoli cells isolated from 5, 11, and 20 day-old rats, representing proliferating, differentiating, and differentiated cells, respectively. DNA binding by E-box proteins is nearly undetectable at 5 days after birth but peaks with initiation of differentiation at 11 days after birth and remains elevated. Upstream Stimulatory Factors 1 and 2 (USF1, USF2) were the predominant E-box proteins present within DNA-protein complexes formed after incubating E-box containing probes with nuclear extracts from developing Sertoli cells. Increased USF binding activity corresponded with elevated Usf1 mRNA and USF1 protein levels 11 days after birth. The potentiator of Sertoli cell differentiation, thyroxine, induces USF DNA binding in Sertoli cells prior to differentiation. Decreased nuclear expression of ID proteins may permit increased USF DNA binding during Sertoli cell differentiation. Several genes required for Sertoli cell differentiation and differentiated Sertoli cell functions have USF binding sites within their promoters. Two potential USF target genes, Nr5a1 and Shbg, were induced in 11 day-old Sertoli cells when compared with 5 day-old Sertoli cells. DNA binding studies of Nr5a1 and Shbg promoter sequences determined that USF1 and USF2 binding to E-box motifs increased during differentiation. In vivo binding assays confirmed that USF1 and USF2 occupy the E-box within the Nr5a1 promoter. These data support the ideas that increased USF protein expression induces differentiation-associated gene expression and that USF-mediated alterations in gene transcription are responsible for the onset of differentiation in developing Sertoli cells. These USF-mediated processes would then determine the final number of Sertoli cells present within the testes and the upper limit of fertility.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-06162009-124023 |
| Date | 13 July 2009 |
| Creators | Wood, Michelle Anne |
| Contributors | Shivalingappa Swamynathan, Edward Prochownik, William H. Walker, Anthony Zeleznik, Jennifer Condon-Jeyasuria |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-06162009-124023/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
Page generated in 0.0014 seconds