Analysis of β cell differentiation in diabetic pancreas induced by betacellulin with special reference to the role of Pax family gene

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In the development of endocrine pancreas, various transcription factors that regulate the expression of growth and differentiation factors are involved. Among them, Pax family is known to have important role in the final differentiation of insulin-secreting β cells. On the other hand, little is known in the mechanism of neogenesis which occurs in the β cell depleted diabetic pancreas. We thus studied the process of β cell neogenesis with special reference to the expression of transcription factors including Pax family in pancreas of glucose intolerant mice induced by selective alloxan perfusion. We also tried to clarify the role of Pax 6 and 4 using dominant negative form of these genes introduced in AR42J cells. ICCs(Islet-like cell clusters) were observed closely associated with duct cell lining, and immunohistochemical analysis revealed that several kinds of transcription factors including PDX-1, Islet1, Nkx2.2 and Pax6 were expressed in some of duct cells and Icc cells, suggesting that Pax6 is involved in the β cell neogenesis in diabetic pancreas and the process of this type of regeneration (neogenesis) was similar to that of fetal endocrine cell development . However, Pax4 which is important for the final differentiation of β cells during development was undetectable level. Treatment with betacellulin , one of the growth factor of EGF family and is known to induce differentiation of AR42J cells into insulin-producing endocrine cells, increased the number of ICCs and ameliorate the glucose intolerance. To clarify the role of Pax4 and Pax6 in the β cell differentiation, we tried to make stable transformants of dominant negative form of these genes in AR42J cells, but this was difficult, and we could not analyze the roles of two Pax genes in β cell differentiation using in vitro experimental system.