Biomedical subjects

John Brestelli

Publications and source records attributed to John Brestelli.

5 recordsLinked to original sources

PubMed2006

EPConDB: a web resource for gene expression related to pancreatic development, beta-cell function and diabetes.

EPConDB (http://www.cbil.upenn.edu/EPConDB) is a public web site that supports research in diabetes, pancreatic development and beta-cell function by providing information about genes expressed in cells of the pancreas. EPConDB displays expression profiles for individual genes and information about transcripts, promoter elements and transcription factor binding sites. Gene expression results are obtained from studies examining tissue expression, pancreatic development and growth, differentiation of insulin-producing cells, islet or beta-cell injury, and genetic models of impaired beta-cell function. The expression datasets are derived using different microarray platforms, including the BCBC PancChips and Affymetrix gene expression arrays. Other datasets include semi-quantitative RT-PCR and MPSS expression studies. For selected microarray studies, lists of differentially expressed genes, derived from PaGE analysis, are displayed on the site. EPConDB provides database queries and tools to examine the relationship between a gene, its transcriptional regulation, protein function and expression in pancreatic tissues.

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PubMed2006

Novel genes identified by manual annotation and microarray expression analysis in the pancreas.

The mouse PancChip, a microarray developed for studying endocrine pancreatic development and diabetes, represents over 13,000 cDNAs. After computationally assigning the cDNAs on the array to known genes, manual curation of the remaining sequences identified 211 novel transcripts. In microarray experiments, we found that 196 of these transcripts were expressed in total pancreas and/or pancreatic islets. Of 50 randomly selected clones from these 196 transcripts, 92% were confirmed as expressed by qRT-PCR. We evaluated the coding potential of the novel transcripts and found that 74% of the clones had low coding potential. Since the transcripts may be partial mRNAs, we examined their translated proteins for transmembrane or signal peptide domains and found that about 40 proteins had one of these predicted domains. Interestingly, when we investigated the novel transcripts for their overlap with noncoding microRNAs, we found that 1 of the novel transcripts overlapped a known microRNA gene.

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PubMed2006

Identification of transcriptional targets during pancreatic growth after partial pancreatectomy and exendin-4 treatment.

After partial pancreatectomy (Ppx), substantial regeneration of the endocrine and exocrine pancreatic compartments has been shown in adult rodents. Exendin-4 (Ex-4) is a glucagon-like peptide-1 receptor agonist that augments endocrine beta-cell mass by stimulating neogenesis, proliferation, and cell survival. After Ppx, treatment with Ex-4 ameliorates hyperglycemia by stimulating beta-cell mass recovery. We utilized a cDNA microarray approach to identify genes differentially regulated during pancreatic regeneration after Ppx and/or Ex-4 administration. The pancreatic remnant after Ppx showed a large number of differentially regulated genes. In contrast, Ex-4 treatment resulted in a smaller number of differentially regulated genes. Of note, a common subset of genes regulated by Ex-4 and after Ppx was identified, including three members of the mitogenic Reg gene family, Reg2, -3gamma, and -3beta, as well as fragilis, a gene that maintains pluripotency during germ cell specification, and Serpin b1a, a member of an intracellular protease inhibitor family involved in cell survival. These observations were confirmed by real-time PCR. We determined that Reg3beta protein is also induced in the acinar pancreas after Ppx, suggesting a novel role for this factor in pancreatic growth or response to injury. Finally, comparison of transcription factor-binding sites present in the proximal promoters of these genes identified potential common transcription factors that may regulate these genes. Chromatin immunoprecipitation analyses confirmed Reg3gamma as a novel transcriptional target of Foxa2 (HNF3beta). Our data suggest molecular pathways that may regulate pancreatic growth and offer a unique set of candidate genes to target in the development of therapies aimed at improving pancreatic growth and function.

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PubMed2005

Transcriptional networks in the liver: hepatocyte nuclear factor 6 function is largely independent of Foxa2.

A complex network of hepatocyte nuclear transcription factors, including HNF6 and Foxa2, regulates the expression of liver-specific genes. The current model, based on in vitro studies, suggests that HNF6 and Foxa2 interact physically. This interaction is thought to synergistically stimulate Foxa2-dependent transcription through the recruitment of p300/CBP by HNF6 and to inhibit HNF6-mediated transcription due to the interference of Foxa2 with DNA binding by HNF6. To test this model in vivo, we utilized hepatocyte-specific gene ablation to study the binding of HNF6 to its targets in the absence of Foxa2. Chromatin immunoprecipitation using anti-HNF6 antibodies was performed on chromatin isolated from Foxa2(loxP/loxP) Alfp.Cre and control mouse livers, and HNF6 binding to its target, Glut2, was determined by quantitative PCR. In contrast to the current model, we found no significant difference in HNF6 occupancy at the Glut2 promoter between Foxa2-deficient and control livers. In order to evaluate the Foxa2/HNF6 interaction model on a global scale, we performed a location analysis using a microarray with 7,000 mouse promoter fragments. Again, we found no evidence that HNF6 binding to its targets in chromatin is reduced in the presence of Foxa2. We also examined the mRNA levels of HNF6 targets in the liver using a cDNA array and found that their expression was similar in Foxa2-deficient and control mice. Overall, our studies demonstrate that HNF6 binds to and regulates its target promoters in vivo in the presence and absence of Foxa2.

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PubMed2004

Mild nephrogenic diabetes insipidus caused by Foxa1 deficiency.

Foxa1 is a member of the winged helix family of transcription factors and is expressed in the collecting ducts of the kidney. We investigated its potential contribution to renal physiology in Foxa1-deficient mice on a defined genetic background. Foxa1(-/-) mice are dehydrated and exhibit electrolyte imbalance as evidenced by elevated hematocrit and plasma urea levels, hypernatremia, and hyperkalemia. This phenotype is the consequence of decreased urine osmolality secondary to renal vasopressin resistance. Mutations of the human genes encoding the vasopressin 2 receptor and aquaporin 2 cause nephrogenic diabetes insipidus; however, expression of these genes is maintained or increased, respectively, in Foxa1(-/-) mice. Likewise, expression of the genes encoding the Na-K-2Cl cotransporter (NKCC2), the potassium channel ROMK, the chloride channel CLCNKB, barttin (BSND), and the calcium-sensing receptor (CASR), each of which is important in sodium reabsorption in the loop of Henle, is maintained or even increased in Foxa1-deficient mice. Thus, we have shown that Foxa1(-/-) mice represent a new model of nephrogenic diabetes insipidus with unique molecular etiology, and we have identified the first transcription factor whose mutation leads to a defect in renal water homeostasis in vivo.

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