Evaluation of endocrine pancreas development and maturation in glis3 mutant zebrafish (Danio rerio)

The transcription factor Gli-similar 3 (Glis3) has been shown to play critical roles in the development and maintenance of insulin producing β-cells. Mutations within the human GLIS3 locus are associated with several pathologies including diabetes mellitus. Currently, little is known about the roles Glis3 plays in pancreatic cell-fate specification or its involvement in the postnatal expansion of β-cell mass. Using zebrafish as a model, we have characterized glis3 expression during development using whole mount in situ hybridization and RT-PCR. By 72 hpf, glis3 expression was evident within the pancreas suggesting a possible role in secondary islet generation. These data were supported by morpholino knockdown of glis3, which resulted in decreased insulin transcription at 5 dpf. To better understand the role(s) of glis3 in β-cell maturation and expression, zebrafish were generated that lack functional glis3 expression due to an ENU mutagenesis-induced nonsense mutation within exon2 of glis3, resulting in a protein truncated at Thr47 that lacks its DNA binding transactivation domains (glis3sa17645). In order to determine whether glis3 haploinsufficiency resulted in impaired β-cell mass expansion in response to nutrient excess, wildtype and glis3+/sa17645heterozygotes were fed a normal or high-fat/high-glucose diet and were subsequently analyzed for insulin production and blood glucose levels. Collectively, these studies indicate that glis3 has roles in specifying endocrine cell fates during zebrafish pancreas development and may regulate mass expansion in the mature organism. Characterization of glis3 in zebrafish may lead to the identification of therapeutic targets for the treatment of diabetes or other glis3-associated diseases