Neurogenin-3 (NEUROG3) is expressed in endocrine progenitor cells and is required for endocrine cell development in the pancreas and intestine (Wang et al., 2006). It belongs to a family of basic helix-loop-helix transcription factors involved in the determination of neural precursor cells in the neuroectoderm (Gradwohl et al., 2000).

By in situ hybridization, Sommer et al. (1996) found that mouse Ngn3 was most strongly expressed in a restricted region of the developing spinal cord, just dorsal to the floor plate. Expression was detectable as early as embryonic day 9 and persisted until day 14. Ngn3 was also expressed in the developing hypothalamic region and in pancreatic islet cell progenitors.

Sommer et al. (1996) determined that the mouse Ngn3 gene contains a single coding exon.

Spence et al. (2011) established a robust and efficient process to direct the differentiation of human pluripotent stem cells into intestinal tissue in vitro using a temporal series of growth factor manipulations to mimic embryonic intestinal development. Using this culture system as a model to study human intestinal development, Spence et al. (2011) identified that the combined activity of WNT3A (606359) and FGF4 (164980) is required for hindgut specification, whereas FGF4 alone is sufficient to promote hindgut morphogenesis. Spence et al. (2011) also determined that NEUROG3 is both necessary and sufficient for human enteroendocrine cell development in vitro. Spence et al. (2011) concluded that human intestinal stem cells form de novo during development.

Talchai et al. (2012) showed that, unexpectedly, somatic ablation of Foxo1 (136533) in Neurog3+ enteroendocrine progenitor cells gives rise to gut insulin-positive cells that express markers of mature beta cells and secrete bioactive insulin as well as C peptide in response to glucose and sulfonylureas. Lineage tracing experiments showed that gut insulin-positive cells arise cell autonomously from Foxo1-deficient cells. Inducible Fox1 ablation in adult mice also resulted in the generation of gut insulin-positive cells. Following ablation by the beta-cell toxin streptozotocin, gut insulin-positive cells regenerated and produced insulin, reversing hyperglycemia in mice. Talchai et al. (2012) concluded that their data indicated that Neurog3+ enteroendocrine progenitors require active Foxo1 to prevent differentiation into insulin-positive cells, and suggested that Foxo1 ablation in gut epithelium may provide an approach to restore insulin production in type 1 diabetes.

By immunoprecipitation and mass spectrometric analysis in HEK293A cells, Manea et al. (2023) identified USP7 (602519) as an interacting partner of NGN3. USP7 deubiquitinated and stabilized NGN3 by preventing its proteasomal degradation. Mice with conditional pancreas-specific deletion of Usp7 had reduced body weight, reduced endocrine lineage specification, and diabetes due to defective pancreatic development, as Usp7 regulated Ngn3-mediated endocrine formation during development. Consequently, Usp7 loss severely impacted the endocrine compartment in mutant mice, but not the exocrine compartment. Database analysis indicated that USP7 expression preceded NGN3 expression during human pancreas development, similar to its role in murine pancreas development. Moreover, USP7 inhibition impaired beta-cell differentiation in human induced-pluripotent stem cell-derived pancreas organoids.

Congenital Malabsorptive Diarrhea 4 with Diabetes Mellitus and Combined Pituitary Hormone Deficiency

In 3 unrelated boys with congenital malabsorptive diarrhea (DIAR4; 610370), Wang et al. (2006) identified 2 different homozygous mutations in the NEUROG3 gene (604882.0001; 604882.0002). Both mutations rendered the NEUROG3 protein unable to activate NEUROD1 (601724), a downstream target of NEUROG3, and compromised the ability of NEUROG3 to bind to an E-box element in the NEUROD1 promoter. The injection of wildtype but not mutant NEUROG3 mRNA into Xenopus embryos induced NEUROD1 expression. The authors referred to the disorder in these boys as 'enteric anendocrinosis.'

In a 5-year-old Chilean girl with severe congenital malabsorptive diarrhea and permanent neonatal diabetes mellitus, Rubio-Cabezas et al. (2011) identified compound heterozygosity for a nonsense (E28X; 604882.0003) and a missense mutation (L135P; 604882.0004) in the NEUROG3 gene. Her unaffected parents were each heterozygous for 1 of the mutations, neither of which was found in 334 control chromosomes or in public variant databases. Functional analysis demonstrated complete loss of function with the L135P variant, whereas the E28X variant showed very limited to no activity compared to wildtype NEUROG3.

In a female infant of Ecuadorian ancestry with congenital malabsorptive diarrhea and neonatal diabetes, who was negative for mutation in known neonatal diabetes-associated genes, Pinney et al. (2011) sequenced the NEUROG3 gene and identified homozygosity for a nonsense mutation (E123X; 604882.0005). Functional analysis showed significantly reduced activity with the mutant compared to wildtype NEUROG3.

In a 20-month-old Turkish girl with intractable malabsorptive diarrhea due to enteric anendocrinosis, who had normal serum glucose levels, Sayar et al. (2013) identified homozygosity for a 1-bp duplication in the NEUROG3 gene (604882.0006). Her unaffected first-cousin parents were both heterozygous for the duplication.

Rubio-Cabezas et al. (2014) reported 4 patients from 3 families with DIAR4 who were homozygous for previously reported missense mutations in the NEUROG3 gene (see 604882.0001 and 604882.0004). All 4 patients had congenital malabsorptive diarrhea, 3 had diabetes mellitus, and 2 exhibited pancreatic exocrine insufficiency. All 4 patients also exhibited short stature and hypogonadotropic hypogonadism. The authors reviewed the 7 previously reported cases of DIAR4 and stated that there was no apparent genotype-phenotype correlation between specific NEUROG3 mutations and pancreatic endocrine function. They noted that NEUROG3 deficiency could result in various phenotypes of diabetes, including permanent neonatal diabetes, relapsing transient neonatal diabetes, and childhood-onset permanent diabetes.

In a Jordanian male infant with congenital malabsorptive diarrhea, born of first-cousin parents, Azab et al. (2020) identified homozygosity for a missense mutation in the NEUROG3 gene (T138R; 604882.0007). His unaffected mother was heterozygous for the mutation, and an unaffected brother did not carry the mutation; DNA was unavailable from the father.

In a 17-month-old boy with congenital malabsorptive diarrhea and diabetes, Francis et al. (2022) identified homozygosity for a missense mutation in the NEUROG3 gene (I132F; 604882.0008).

In 3 unrelated Thai teenagers with malabsorptive diarrhea due to enteric anendocrinosis, diabetes mellitus, short stature, and delayed puberty, Wejaphikul et al. (2023) identified homozygosity for missense mutations in the NEUROG3 gene: patient 1 was homozygous for a T124R substitution (604882.0009) and patients 2 and 3 were homozygous for an R95P substitution (604882.0010). All 3 patients exhibited multiple pituitary hormone deficiencies, patients 1 and 3 had pituitary gland hypoplasia, and patients 2 and 3 also had proximal renal tubulopathy. Luciferase reporter assay demonstrated that both variants impaired transcriptional activity of NEUROG3.

Exclusion Studies

Kim et al. (2001) concluded that genetic variability in neurogenin-3 gene does not contribute to the etiology of maturity-onset diabetes of the young (see 125853) or other forms of autosomal dominant diabetes.

Mouse Ngn3 is expressed in discrete regions of the nervous system and in scattered cells in the embryonic pancreas (Sommer et al., 1996). Gradwohl et al. (2000) showed that Ngn3-positive cells did not express insulin or glucagon, suggesting that Ngn3 marks early precursors of pancreatic endocrine cells. Mice lacking Ngn3 function failed to generate any pancreatic endocrine cells and died postnatally from diabetes. Expression of the pancreatic transcription factors Isl1 (600366), Pax4 (167413), Pax6 (607108), and NeuroD (601724) was lost, and endocrine precursors were lacking in the mutant pancreatic epithelium. Thus, Ngn3 was required for the specification of a common precursor of the 4 pancreatic endocrine cell types.

Lee et al. (2002) found that glucagon-secreting A cells, somatostatin-secreting D cells, and gastrin-secreting G cells were absent from the epithelium of the glandular stomach of Ngn3 -/- mice, and the number of serotonin-expressing enterochromaffin cells was dramatically decreased. In addition, Ngn3 -/- mice displayed intestinal metaplasia of the gastric epithelium. Lee et al. (2002) concluded that NGN3 is required for differentiation of enteroendocrine cells in the stomach and maintenance of gastric epithelial cell identity.

Zhou et al. (2008) used a strategy of reexpressing key developmental regulators in vivo to identify a specific combination of 3 transcription factors, Neurog3, Pdx1 (600733), and Mafa (610303), that reprogrammed differentiated pancreatic exocrine cells in adult mice into cells that closely resembled beta cells. Induced beta cells were indistinguishable from endogenous islet beta cells in size, shape, and ultrastructure. They expressed genes essential for beta cell function and could ameliorate hyperglycemia by remodeling local vasculature and secreting insulin. Zhou et al. (2008) concluded that their study provided an example of cellular reprogramming using defined factors in an adult organ and suggested a general paradigm for directing cell reprogramming without reversion to a pluripotent stem cell state.