A Specific CNOT1 Mutation Results in a Novel Syndrome of Pancreatic Agenesis and Holoprosencephaly through Impaired Pancreatic and Neurological Development

Abstract

We report a recurrent CNOT1 de novo missense mutation, GenBank: NM_016284.4; c.1603C>T (p.Arg535Cys), resulting in a syndrome of pancreatic agenesis and abnormal forebrain development in three individuals and a similar phenotype in mice. CNOT1 is a transcriptional repressor that has been suggested as being critical for maintaining embryonic stem cells in a pluripotent state. These findings suggest that CNOT1 plays a critical role in pancreatic and neurological development and describe a novel genetic syndrome of pancreatic agenesis and holoprosencephaly.

Keywords: agenesis; development; diabetes; genetics; mutation; neonatal; neurological; pancreas.

Figure 1

Genetic and Clinical Findings in Individuals with Pancreatic Agenesis (A) Partial pedigrees and clinical features of the three individuals with the heterozygous CNOT1 p.Arg535Cys mutation. (B) Conservation of CNOT1 residues 529 to 568 across 10 representative species. Residue p.Arg535 is highlighted in red. Residues identical to the human CNOT1 protein are highlighted in blue, differences are highlighted in gray. (C) Coronal brain MRI of P02 showing absence of the anterior interhemispheric fissure (red arrow), fusion of the frontal lobes (orange arrow), absence of frontal horns (green arrow), absence of the sylvian fissures (yellow arrow). Splenium of the corpus callosum is visible (blue arrow). (D) Post mortem image of P02’s liver (L), spleen (S), and duodenum (D). White arrow shows the orthotopic location of the pancreas, which is absent. Dashed arrow indicated site in which the absent gallbladder would be expected to be.

Figure 2

Neurological and Pancreatic Abnormalities in Mouse Embryos Homozygous for the Cnot1 p.Arg535Cys Mutation (A) Table listing the gross external phenotypes observed in E14.5 embryos. Numbers do not add to total as many embryos displayed multiple phenotypes. Significance by Fisher’s exact test, assuming an additive model. Exencephaly, p = 3.2 × 10⁻⁹; spina bifida, p = 0.027; eye defect, p = 5.5 × 10⁻⁸; edema, p = 2.6 × 10⁻⁷; midline defect, ns. (B) Images showing representative E14.5 embryos: top shows wild-type embryo, bottom shows embryo homozygous for the CNOT1 p.Arg535Cys mutation with exencephaly and coloboma. (C and E) Coronally sectioned, semi-transparent 3D volume models of stage-matched E14.5 embryos with superimposed models of the pancreas of homozygous (C) and wild-type (E) embryos. (D) Overlay of extracted surface models of the pancreas of homozygous (blue, magenta) and wild-type embryos (orange, green). (F and G) Coronally sectioned solid 3D volume rendered model of the abdomen of the embryos shown in (C) and (E) with superimposed pancreas. dp, dorsal pancreas; vp, ventral pancreas; li, liver lobes; s, stomach; sp, spleen; k, kidney; g, gonad; bd, bile duct. Scale bars: 1,000 μm in (C), (E)–(G); 500 μm in (D). (H) Graph showing the volume of the dorsal pancreas of E14.5 embryos in μm³. Blue squares show wild types, green circles are heterozygotes, and red triangles are homozygotes. Data analyzed using ANOVA with TukeyHSD posthoc test, effect of genotype p = 8.85 × 10⁻⁸; post hoc WT-Hom, p < 10⁻¹⁰; Het-Hom, p = 1.36 × 10⁻⁴, WT-Het, ns.

Figure 3

Expression Data and Possible Mechanism Involving CNOT1 in Pancreatic Development (A) Graphs showing relative expression of genes in the pancreas of E14.5 embryos. Bars show mean ± SE. Data analyzed using ANOVA with TukeyHSD posthoc test. Results of posthoc tests shown on graphs, ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001. Shh, effect of genotype p = 0.0107; Pdx1, effect of genotype p = 0.0189; Ins, effect of genotype p = 7.03 × 10⁻⁶; Hnf1b, effect of genotype p = 0.0294; Ptf1a, effect of genotype p = 0.00781; Gata6, effect of genotype p = ns. n = 4–12 animals per genotype. (B) Schematic representation of the proposed role for CNOT1 in pancreatic development.