Immunohistochemical Characterization of Insulin, Glucagon, PDX1, SOX17 and NGN3 Expression in Human Fetal Pancreatic Development

Examination of human fetal pancreatic endocrine cell development can provide further insight in, defining the developmental patterns of endocrine cells and identifying β-cell progenitors. In this study we performed a comprehensive immunohistochemical analysis of human fetal pancreatic sections aged from 7.7 to 38 weeks post conception (wpc), as well as 10 weeks post natal (wpn), and adult sections. We examined expression and co-expression of insulin, glucagon, cytokeratin19 (CK19), vimentin as well as the transcription factors PDX1, SOX17 and NGN3. Insulin and glucagon expression significantly increased in the first (1-12 wpc) and second (13-24 wpc) trimesters and formed islet-like clusters which resembled adult human islets in the third (24-38 wpc) trimester. Insulin and glucagon coexpressing cells were observed from 8.4 to 23 wpc and peaked during the first trimester. PDX1 expression was observed predominantly in duct-like structures prior to 15 wpc, then, was localized to islet structures in the second trimester at 17 wpc. Co-localization of PDX1 and insulin was observed throughout fetal development and in most insulin cells. SOX17 expressing cells were in spatial proximity to the glucagon expressing cells late in the first and second trimesters and did not co-express either insulin or glucagon. NGN3 was detected from 7.7 to 14.4 wpc within the pancreatic mesenchyme. Expression peaked between 10.6-12.1 wpc and was not detected past 15 wpc. NGN3 cells co-expressed vimentin but did not co-express insulin or CK19. We present a unique qualitative assessment of insulin, glucagon, PDX1, SOX17 and NGN3 expression and co-expression patterns, during human fetal pancreatic development. In combination with in vitro human embryonic stem cell isolation studies, in vivo characterization of β-cell progenitors during fetal development, will improve progenitor cell isolation and differentiation of viable β-cell progenitors destined for transplantation.