Genetic analysis of early vertebrate endocrine pancreas formation

Vertebrate endocrine pancreas consists of four different cells types arranged in a characteristic structure. We investigated molecular mechanisms directing endocrine pancreas development.; We assessed the participation of Wnt signaling in pancreatic islet formation. Signaling by the Wnt family of secreted glycoproteins through their receptors, the frizzled (Fz) family of seven-pass transmembrane proteins, is critical for numerous cell fate and tissue polarity decisions during development. Using zebrafish, we demonstrated that insulin-positive cells actively migrate to form an islet. We used morpholinos (MOs) and time-lapse imaging analysis to show that the Wnt-5/Fz-2 signaling is required for proper insulin-cell migration in zebrafish. Histological analyses of islets in Wnt5a-/- mouse embryos showed that Wnt5a signaling is also critical for murine pancreatic insulin -cell migration.; We also combined in situ hybridization methods to visualize the pancreatic islet with an ENU mutagenesis screen to identify novel genes involved during the early process of a pancreatic islet formation in zebrafish. We screened 900 genomes and found 12 mutations belonging to 9 different complementation groups. These mutants fall into three major phenotypic classes displaying severely reduced insulin expression, reduced insulin expression with abnormal islet morphology, or abnormal islet morphology with a relatively normal number of insulin expressing cells.; Finally, we investigated a role of variant hepatocyte nuclear factor-1 (vhnf-1) in zebrafish pancreas and liver development and disease. Msl was mapped to vhnf-1 locus by a positional cloning method. Of note, vhnf-1 msl mutants exhibit more severe defects in endocrine pancreas formation than previously identified vhnf-12960, arguing for a different molecular mechanism leading to a more severe mutant phenotype. We show that vhnf-1 is epistatic to RA in pancreatic islet formation. In addition, our analysis showed that the male vhnf-1 msl carriers have high incidence of liver cancer.; Our data provide evidence for the conserved requirement of wnt-5/fz-2 signaling in insulin cell migration, RA/vhnf-1 signaling in early endocrine cell specification, and the processes of early endocrine pancreatic cell specification and migration. These studies suggest a need for further investigation into the participation of Wnt and RA signaling in vertebrate organ development and disease.