The Developmental Biology of the Psammomys obesus Pancreas: Cloning and Expression of the Neurogenin-3 Gene
Louise Vedtofte 1, Thóra B. Bödvarsdóttir 1, Allan E. Karlsen 1 and R. Scott Heller 1*
1 Department of Developmental Biology, Hagedorn Research Institute, Gentofte, Denmark (LV,RSH); Department of Diabetes Pharmacology (TBB) and Department of Insulin, Incretin, and Islet Biology (AEK), Novo Nordisk, Måløv, Denmark; and Institute for Clinical Science, University of Lund, Lund, Sweden (AEK)
* To whom correspondence should be addressed. E-mail: shll{at}hagedorn.dk .
Submitted on August 7, 2006
Accepted on 5 September 2006
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Abstract |
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The desert gerbil Psammomys obesus is a well established model of type 2 diabetes (T2D) that has previously been shown to lack Pdx-1 (pancreatic and duodenal homeobox gene 1) expression. Pdx-1-deficiency leads to pancreas agenesis in both mouse and man and we have therefore further examined the development of the pancreas of P. obesus at embryonic day (E) 14.5, 18.5, and 22.5 of gestation, equivalent to mouse E10-10.5, E12.5 and E17, respectively. Using Pdx-1 antisera raised against evolutionary conserved epitopes (from Xenopus to man) we fail to detect Pdx-1 immunoreactivity at any time points. However, at E14.5 Nkx6.1 immunoreactivity marks the nuclei of all epithelial cells of the ventral and dorsal pancreatic buds and the only endocrine cell types found at this time point are glucagon and PYY and thus P. obesus is very similar to the mouse. At E18.5 the pancreas is well branched and both glucagon and ghrelin positive cells are scattered or found in clusters, while insulin positive cells are not found. At E22.5, the acini of the exocrine pancreas are starting to mature and amylase and carboxypeptidase A immunoreactivity is found scattered and not in all acini. Ghrelin, glucagon, PYY, gastrin, somatostatin (SS), pancreatic polypeptide (PP) and insulin immunoreactive cells are found scattered or in small groups within or lining the developing ductal epithelium as marked by cytokeratin 19. Nkx2.2 and Pax6 immunoreactivity is localized to most endocrine cell types. Using a degenerate PCR approach followed by 5' and 3' RACE, the P. obesus Ngn-3 gene was cloned. The nucleotide and amino acid sequences show high homology with the rat, mouse and human sequences. Using antiserum raised against the mouse protein, we can observe that Ngn-3 immunoreactive cells are rare at E14.5 but readily detectable at E18.5 and E22.5. In conclusion, despite the lack of detection of Pdx-1, the P. obesus pancreas develops similarly to Muridae species and the Ngn-3 sequence and expression pattern is highly conserved in P. obesus.
Key Words:
Psammomys obesus, Neurogenin-3, Type 2 diabetes, developmental biology, glucagon, insulin, pancreas, sand rat
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