cDNA cloning and mRNA expression of canine pancreatic and duodenum homeobox 1 (Pdx-1)

Pancreatic and duodenal homeobox 1 (Pdx-1) is a critical insulin transcription factor expressed by pancreatic β-cells, and is crucial in the early stage of pancreas development. Unfortunately, nothing concerning Pdx-1 in canine has been elucidated yet. In this study, full length canine Pdx-1 cDNA was cloned and it was 1498 bp in length, consisting of a 99 bp 5'-untranslated region (UTR), a 849 bp coding region, and a 550 bp 3'-UTR region. A deduced 282 amino acid sequence of canine PDX-1 displayed high overall sequence identity with human, bovine, and mouse PDX-1. qRT-PCR analysis revealed that a high level of Pdx1 mRNA expression is exists in the duodenum and pancreas of canines. In addition, functional canine insulin promoter-luciferase reporter constructs with various canine insulin promoter region fragments revealed that our Pdx-1 isolated cDNA sequence encodes for a functionally active PDX-1 protein. Significant promoter activity was observed within the -583 bp 5'-upstream region of canine insulin gene with Chinese hamster ovary cells. In addition, Pdx-1 appears to have a synergistic effect with beta cell transactivator 2 (BETA2) and V-maf avian musculoaponeurotic fibrosarcoma oncogene homolog A (MafA), which also have important roles in the activation of the insulin gene promoter. Our results confirm that similar to humans, Pdx1 plays an important role in expression of insulin gene in canines.