Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/17080
Title: Mechanisms of hormonally-induced transcription of LHBeta subunit gene in its chromatin setting
Authors: KOH MINGSHI
Keywords: Luteinizing hormone,Chromatin immunoprecipitation,estrogen receptor, histone deacetylation,gonadotropin releasing hormone,plasmid immunoprecipitation
Issue Date: 9-May-2005
Source: KOH MINGSHI (2005-05-09). Mechanisms of hormonally-induced transcription of LHBeta subunit gene in its chromatin setting. ScholarBank@NUS Repository.
Abstract: Luteinizing hormone (LH) is crucial in reproduction as it regulates gonadal function. Its synthesis is tightly regulated in a cyclical manner, mostly by gonadotropin releasing hormone (GnRH) and gonadal steroids which are secreted from the hypothalamus and gonads respectively. The aim of this study was to investigate the transcriptional regulation of the LHI? subunit gene in its native chromatin setting. Chromatin immunoprecipitation (ChIP) technique, which allows the study of in vivo interaction between protein and DNA was used. It allows the elucidation of the transcription factors bound to the gene, and the specific modifications on the histone tails at the gene locus. A modification to the ChIP assay, plasmid immunoprecipitation (PIP), was developed which allows for the first time, the in vivo study of the recruitment of transcription factors and co-activators by specific cis-elements. In this way, it was shown that ERI?, which activates the salmon LHI? gene alone or with Sf-1 and Pitx-1, binds the gene promoter without requiring an ERE (estrogen response element) but appears to be recruited to the promoter through the Sf-1 binding site. Similarly, ERI? binds and activates the rat LHI? gene promoter, which like the other mammalian LHI? promoters, lacks the consensus ERE. It was further shown that this element facilitates the binding and transactivation of the Chinook salmon LHI? (csLHI?) promoter by c-Jun. Transactivation of the LHI? gene promoter was further studied using ChIP to examine the ERI? association with the promoter. Treatment of the cells with GnRH lengthen the duration of ERI? cycling on and off the promoter and increased the amount of LHI? gene promoter associated with the ERI?. An initial study showed that the expression of gonadotropin subunit genes, LHI? and FSHI? is repressed in immature gonadotropes by deacetylation but this appears to be overcome by GnRH. The GnRH-induced regulation of the pituitary gonadotropin hormones from the native chromatin template via GnRH was thus studied for the first time with ChIP using antibodies to the acetylated lysine residues on the H3 and H4 histone tails. Increased acetylation was observed at the histones associated with LHI? gene promoter. A number of histone deacetylases (HDACs) were also identified to be involved in the repression of both hormones, some in a gene specific manner. It is thus suggested that distinct co-repressor complexes are recruited to regulate repression of these genes at specific stages of the reproductive life history.
URI: http://scholarbank.nus.edu.sg/handle/10635/17080
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