Analysis of Transcription Factors Key for Mouse Pancreatic Development Establishes NKX2-2 and MNX1 Mutations as Causes of Neonatal Diabetes in Man

Abstract

SummaryUnderstanding transcriptional regulation of pancreatic development is required to advance current efforts in developing beta cell replacement therapies for patients with diabetes. Current knowledge of key transcriptional regulators has predominantly come from mouse studies, with rare, naturally occurring mutations establishing their relevance in man. This study used a combination of homozygosity analysis and Sanger sequencing in 37 consanguineous patients with permanent neonatal diabetes to search for homozygous mutations in 29 transcription factor genes important for murine pancreatic development. We identified homozygous mutations in 7 different genes in 11 unrelated patients and show that NKX2-2 and MNX1 are etiological genes for neonatal diabetes, thus confirming their key role in development of the human pancreas. The similar phenotype of the patients with recessive mutations and mice with inactivation of a transcription factor gene support there being common steps critical for pancreatic development and validate the use of rodent models for beta cell development.

Human pancreas development

“…Interestingly, inactivation of Mnx1 in mouse causes dorsal pancreas agenesis because of deficiencies in the peripancreatic mesenchyme (Harrison et al, 1999;Li et al, 1999). However, in human, inactivating mutations in MNX1 cause permanent neonatal diabetes, to date without any evidence of exocrine pancreas failure, implying the primary site of dysfunction is more restricted to the β-cell (Bonnefond et al, 2013;Flanagan et al, 2014).…”

“…Downstream of NEUROG3, four other transcription factors have been identified as causative for PNDM when mutated: NEUROD1 (Rubio-Cabezas et al, 2010), NKX2.2 , PAX6 (Solomon et al, 2009) and MNX1 (Bonnefond et al, 2013;Flanagan et al, 2014). The first three factors are expressed in human β-cells from early fetal development onwards (Lyttle et al, 2008;Jennings et al, 2013), with NEUROD1 and NKX2.2 considered to be direct targets of NEUROG3 action (Sussel et al, 1998;Gradwohl et al, 2000).…”

“…A number of other conditions are also highlighted in which pancreas development is affected. Other causes of monogenic diabetes, including transient neonatal diabetes, are covered expertly elsewhere (Flechtner et al, 2008;Vaxillaire et al, 2012;Rubio-Cabezas and Ellard, 2013;Flanagan et al, 2014;RubioCabezas et al, 2014;Schwitzgebel, 2014).…”

“…Indeed, some of the variants are located close to genes known to be monogenic causes of diabetes when mutated. These genes tend to encode transcription factors that regulate pancreas development in other species Rubio-Cabezas and Ellard, 2013;Flanagan et al, 2014;Rubio-Cabezas et al, 2014;Schwitzgebel, 2014). Moreover, it is now apparent that developmental pathology can be associated with alterations in regulatory elements outside gene coding sequences (Weedon et al, 2014).…”

Inactivating the permanent neonatal diabetes gene Mnx1 switches insulin-producing β-cells to a δ-like fate and reveals a facultative proliferative capacity in aged β-cells

“…Thus, these initial studies suggested that Mnx1 regulates β-cell differentiation and maturation. Furthermore, Mnx1 homozygous mutation was recently shown to cause permanent neonatal diabetes mellitus in humans (Bonnefond et al, 2013;Flanagan et al, 2014), suggesting a potentially conserved role of Mnx1 in β-cell function between mouse and human.…”