Acomys, the closest relatives to Gerbils, do express Pdx-1 protein and have similar islet morphology to Gerbils.

Abstract

Acomys, also called spiny mice, were once used as a diabetes model. We have recently demonstrated that the closest relatives to the Acomys, members of the family Gerbillinae, lack the transcription factor Pdx-1. Therefore, we sought to determine if members of this family also lack Pdx-1, and describe the pancreatic morphology in three different species of Acomys: Acomys cahirinus (Egyptian spiny mouse), Acomys cilicicus (Asia Minor spiny mouse) and Acomys dimidiatus (eastern spiny mouse). We successfully cloned the Acomys Pdx-1 gene and we demonstrate by immunocytochemistry that the Pdx-1 protein is expressed in the pancreatic insulin immunoreactive cells and in a subset of the somatostatin cells. The basic islet structure is very similar to other rodents - with the insulin cells in the center, and glucagon, somatostatin, PP and occasional PYY cells in the periphery. No ghrelin or CART cells were identified. Nkx6.1 was localized specifically to the insulin immunoreactive cells, while Nkx2.2 was found in all endocrine cells except the somatostatin immunoreactive cells. Both MafA and MafB were expressed in the islets; MafA being specific for the insulin cells, while MafB was primarily in the glucagon cells but also found in some insulin cells. Isl-1 was localized in all endocrine cell types. In conclusion, the closest relatives to the Gerbils express a Pdx-1 protein that is 90% similar to other rodents but also has a unique 3 amino acid insert compared to other species.  During the evolution of the spiny mice and the gerbils, it appears that the Pdx-1 gene was lost.