BACKGROUND:In recent years a large number of studies have suggested that bone marrow mesenchymal stem cells can ease hyperglycemia of diabetic rats, but the related mechanism is unclear and controversial. OBJECTIVE:To investigate the relevant mechanism of bone marrow mesenchymal stem cells on pancreas microenvironment in vivo in diabetic rats. METHODS:Bone marrow mesenchymal stem cells were transfected with enhanced green fluorescent protein (EGFP) and administered to diabetic rats via the subcapsular pancreas. Blood glucose levels were monitored. The expressions of the key genes in islet development in these EGFP positive pancreatic cells were analyzed by Real-time quantitative PCR at different times. EGFP and insulin double-positive cells were detected by immunofluorescence. Flow cytometry was performed to analyze cellcycle and DNA ploidy. RESULTS AND CONCLUSION:Blood glucose levels were effectively reduced after transplantation. The expressions of the key genes in islet development reached their own peak values at different times after transplantation:Nestin at week 1, Nkx 2.2 at week 3, Pax 4 and Ngn 3 at week 4, insulin and glucagon at week 12, PDX-1 at week 8 until week 12. The cells double-positive for EGFP and insulin cells were observed. In the pancreas, EGFP positive cells at S+G 2/M phase were significantly increased, and there were no polyploid and aneuploid cells. In pancreas microenvironment, the bone marrow mesenchymal stem cells transplanted into the diabetic pancreas can differentiate into isletβ-like cells under gene control, but not through the fusion with tissue cells.