The diabetes gene Pdx1 regulates the transcriptional network of pancreatic endocrine progenitor cells in mice

Abstract

Heterozygous mutations in the gene encoding the pancreatic homeodomain transcription factor pancreatic duodenal homeobox 1 (PDX1) are associated with maturity onset diabetes of the young, type 4 (MODY4) and type 2 diabetes. Pdx1 governs the early embryonic development of the pancreas and the later differentiation of the insulin-producing islet β cells of the endocrine compartment. We derived a Pdx1 hypomorphic allele that reveals a role for Pdx1 in the specification of endocrine progenitors. Mice homozygous for this allele displayed a selective reduction in endocrine lineages associated with decreased numbers of endocrine progenitors and a marked reduction in levels of mRNA encoding the proendocrine transcription factor neurogenin 3 (Ngn3). During development, Pdx1 occupies an evolutionarily conserved enhancer region of Ngn3 and interacts with the transcription factor one cut homeobox 1 (Hnf6) to activate this enhancer. Furthermore, mRNA levels of all 4 members of the transcription factor network that regulates Ngn3 expression, SRY-box containing gene 9 (Sox9), Hnf6, Hnf1b, and forkhead box A2 (Foxa2), were decreased in homozygous mice. Pdx1 also occupied regulatory sequences in Foxa2 and Hnf1b. Thus, Pdx1 contributes to specification of endocrine progenitors both by regulating expression of Ngn3 directly and by participating in a cross-regulatory transcription factor network during early pancreas development. These results provide insights that may be applicable to β cell replacement strategies involving the guided differentiation of ES cells or other progenitor cell types into the β cell lineage, and they suggest a molecular mechanism whereby human PDX1 mutations cause diabetes. IntroductionInsulin deficiency due to reduced pancreatic islet β cell number underlies the progression of both type 1 and type 2 diabetes, prompting efforts to develop β cell replacement therapies. The high hopes for human islet transplantation as such a therapy have been tempered by their limited availability and short-term function after transplantation, resulting in an intense focus on the development of alternate sources of β cells, through the guided differentiation of stem or progenitor cells or the transdifferentiation of more abundant mature cells. Transdifferentiation approaches have focused largely on the expression of a single or a combination of transcription factors that drive β cell development and differentiation and most have relied, at least in part, upon pancreatic duodenal homeobox 1 (Pdx1), a homeodomain transcription factor with critical regulatory roles in early pancreas development and in the mature β cell (1-5). Recent advances in the derivation of insulin-expressing β-like cells from ES cells (6-11) have also been guided by the principles of embryonic pancreas development (reviewed in ref. 12). Clinical translation of these approaches, however, will require improvements in efficiency, fidelity, and stability of generating the β cell phenotype, efforts which will likely be informed by the identification of novel...

Endocrine Pancreas Development and Regeneration: Noncanonical Ideas From Neural Stem Cell Biology

“…Furthermore, Sox9 occupancy regions on the Ngn3 gene promoter have been identified (104,106). In addition, Sox9 may also regulate Ngn3 via Pdx1 (107,108). (In a seeming paradox, Sox9 also induces Hes1 expression [46], perhaps as a means of limiting its action on Ngn3.…”

Alx3-deficient mice exhibit decreased insulin in beta cells, altered glucose homeostasis and increased apoptosis in pancreatic islets

“…Some of these transcription factors regulate complex transcriptional programmes of gene expression by acting on pancreatic cell specific target gene networks [15,16]. Furthermore, in combination with other transcription factors present in mature cells, they interact co-ordinately on the insulin gene promoter to regulate insulin gene expression [4,17].…”

Emerging roles of GLIS3 in neonatal diabetes, type 1 and type 2 diabetes

“…A number of positive regulators of NGN3, such as PDX1 (Miyazaki et al 2004, Oliver-Krasinski et al 2009), HNF6 (Jacquemin et al 2000), SOX9 (Lynn et al 2007), FOXA2 (Lee et al 2001) and hepatocyte nuclear factor 1β (HNF1β) (Maestro et al 2003) have been identified in the developing pancreas. The expression of NGN3 was drastically reduced in the embryonic pancreata of Glis3 −/− mice both at mRNA and protein levels, compared to that in Glis3 +/+ mice, whereas GLIS3 overexpression significantly upregulated the Ngn3 mRNA in pancreatic ductal cells.…”