GATA4 Is Sufficient to Establish Jejunal Versus Ileal Identity in the Small Intestine

Abstract

Background & AimsPatterning of the small intestinal epithelium along its cephalocaudal axis establishes three functionally distinct regions: duodenum, jejunum, and ileum. Efficient nutrient assimilation and growth depend on the proper spatial patterning of specialized digestive and absorptive functions performed by duodenal, jejunal, and ileal enterocytes. When enterocyte function is disrupted by disease or injury, intestinal failure can occur. One approach to alleviate intestinal failure would be to restore lost enterocyte functions. The molecular mechanisms determining regionally defined enterocyte functions, however, are poorly delineated. We previously showed that GATA binding protein 4 (GATA4) is essential to define jejunal enterocytes. The goal of this study was to test the hypothesis that GATA4 is sufficient to confer jejunal identity within the intestinal epithelium.MethodsTo test this hypothesis, we generated a novel Gata4 conditional knock-in mouse line and expressed GATA4 in the ileum, where it is absent.ResultsWe found that GATA4-expressing ileum lost ileal identity. The global gene expression profile of GATA4-expressing ileal epithelium aligned more closely with jejunum and duodenum rather than ileum. Focusing on jejunal vs ileal identity, we defined sets of jejunal and ileal genes likely to be regulated directly by GATA4 to suppress ileal identity and promote jejunal identity. Furthermore, our study implicates GATA4 as a transcriptional repressor of fibroblast growth factor 15 (Fgf15), which encodes an enterokine that has been implicated in an increasing number of human diseases.ConclusionsOverall, this study refines our understanding of an important GATA4-dependent molecular mechanism to pattern the intestinal epithelium along its cephalocaudal axis by elaborating on GATA4’s function as a crucial dominant molecular determinant of jejunal enterocyte identity. Microarray data from this study have been deposited into NCBI Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo) and are accessible through GEO series accession number GSE75870.

GATA factors in pancreas development and disease

“…GATA factors act as pioneer factors in initiating organ‐specific gene expression during embryonic development . As discussed previously, both Gata4 and Gata6 are expressed in the foregut endoderm and have been reported to be involved in activating liver‐ and intestine‐specific genes, respectively, in the primitive gut tube . However, conditional inactivation of Gata4 and Gata6 in the prepancreatic endoderm using the Foxa3‐Cre driver did not block pancreas specification nor initial pancreas budding .…”

“…49 As discussed previously, both Gata4 and Gata6 are expressed in the foregut endoderm and have been reported to be involved in activating liver-and intestine-specific genes, respectively, in the primitive gut tube. [50][51][52] However, conditional inactivation of Gata4 and Gata6 in the prepancreatic endoderm using the Foxa3-Cre driver did not block pancreas specification nor initial pancreas budding. 53 Thus, GATA4 and GATA6 factors do not seem to be required for pancreas specification in mice.…”

Loss of GATA4 causes ectopic pancreas in the stomach

“…These data suggest that GATA4 maintains glandular stomach cell identity by repressing markers of the anterior stomach. This role is reminiscent of the role of GATA4 in regulating the jejunal‐ileal boundary in the small intestine . The exact mechanism by which GATA4 maintains hindstomach identity remains to be determined.…”

GATA4, expressed in Barrett’s esophagus and esophageal adenocarcinoma, can block squamous epithelial cell gene expression in human esophageal cells

“…previous studies of GATA4 function at the jejunal-ileal intestinal boundary show that GATA4 can act to either activate or repress gene transcription. [31,32] In the jejunum, GATA4 occupies GATA consensus binding sites in chromatin to activate expression of genes typically expressed in the jejunum and to repress expression of genes typically expressed solely in the ileum. This work, along with studies of GATA4 function in tissues like the heart, sets a precedent for GATA4 to act as a transcriptional repressor.…”

“…For a negative control, we used primers to assay GATA4 occupancy at a region in the ubiquitously-expressed Hprt1 gene that lacks GATA4 binding sites and that we have validated as a negative GATA4 ChIP control in other published studies. [32,36,37] GATA4 enrichment at the putative binding sites in squamous cell gene promoters in hindstomach chromatin from GATA4-BIO animals compared with that of control GATA4-WT was measured and expressed as a percentage of input ( Fig. 7C).…”