IA1 is NGN3-dependent and essential for differentiation of the endocrine pancreas

Abstract

Neurogenin 3 (Ngn3) is key for endocrine cell specification in the embryonic pancreas and induction of a neuroendocrine cell differentiation program by misexpression in adult pancreatic duct cells. We identify the gene encoding IA1, a zinc-finger transcription factor, as a direct target of Ngn3 and show that it forms a novel branch in the Ngn3-dependent endocrinogenic transcription factor network. During embryonic development of the pancreas, IA1 and Ngn3 exhibit nearly identical spatio-temporal expression patterns. However, embryos lacking Ngn3 fail to express IA1 in the pancreas. Upon ectopic expression in adult pancreatic duct cells Ngn3 binds to chromatin in the IA1 promoter region and activates transcription. Consistent with this direct effect, IA1 expression is normal in embryos mutant for NeuroD1, Arx, Pax4 and Pax6, regulators operating downstream of Ngn3. IA1 is an effector of Ngn3 function as inhibition of IA1 expression in embryonic pancreas decreases the formation of insulin-and glucagon-positive cells by 40%, while its ectopic expression amplifies neuroendocrine cell differentiation by Ngn3 in adult duct cells. IA1 is therefore a novel Ngn3-regulated factor required for normal differentiation of pancreatic endocrine cells.

Pancreas organogenesis: From bud to plexus to gland

“…Such deficiencies are also observed in Insulinoma-associated antigen 1 (Insm1), Regulatory X-box binding 6 (Rfx6), and Islet1 (Isl1) mutants. Loss of Insm1 or Rfx6 arrests the differentiation of endocrine precursors towards hormone-expressing cells (Gierl et al, 2006;Mellitzer et al, 2006;Soyer et al, 2010;Smith et al, 2010). A phenotype similar to Rfx6 mutant mice has also been reported in human infants carrying mutation in the Rfx6 gene, who have an autosomal recessive syndrome of neonatal diabetes, Mitchell-Riley syndrome (Smith et al, 2010).…”

“…The direct targets of Ngn3 include NeuroD1/ Beta2, Pax4, Arx, Insm1, Rfx6, Nkx2.2, Myt1, and Snail2/Slug (Huang et al, 2000;Smith et al, 2003Smith et al, , 2004Smith et al, , 2010Watada et al, 2003;Mellitzer et al, 2006;Wang et al, 2007;Rukstalis and Habener, 2007;Soyer et al, 2010) (Fig. 2B).…”

Ectopic expression of neurogenin 3 in neonatal pig pancreatic precursor cells induces (trans)differentiation to functional alpha cells

“…Previous studies have indicated that NEUROG3 activates islet transcription factors such as Nkx2.2, Pax4 and IA1 in addition to endodermal transcription factors like Foxa2 and HNF1α, while repressing its own promoter [29][30][31][32]. In this study, interactions between these transcription factors in vitro and in vivo resulted in the rapid transdifferentiation of neonatal pig pancreatic cells into alpha cells.…”

Modifications to the INSM1 promoter to preserve specificity and activity for use in adenoviral gene therapy of neuroendocrine carcinomas

“…The INSM1 mRNA is detected in the developing mouse embryo in the thymus, thyroid, stomach, intestine, pancreas, retina, brain, spinal cord, adrenal glands and pituitary. 20 Studies from our laboratory demonstrated that a 1.7 kbp region of the INSM1 promoter is sufficient to recapitulate the embryonic expression pattern of the INSM1 gene. 19 Importantly, the promoter is not active in normal adult tissues.…”

“…The INSM1 promoter activity was detected in regions overlapping the normal expression pattern of the INSM1 mRNA such as the cerebellum, forebrain, midbrain, hindbrain, spinal cord, thymus, stomach, intestine, pancreas, adrenal gland, pituitary, olfactory bulb and retina in the mouse embryos. 19,20 In addition, the INSM1 promoter-driven b-galactosidase transgene was silenced during late embryonic development mimicking the developmental regulation observed for the INSM1 mRNA. 19 Use of a nonviral INSM1 promoter-driven suicide gene therapy for SCLC has been demonstrated.…”