We also detected transient SOX9 FG-4592 activation during the adaptation of primary islet cells to proliferation in culture , suggesting that cell dedifferentiation also transits through a progenitor-like stage. Our results present an approach for expansion of insulinproducing cells from adult human islets in two stages, the first involving expansion of the mixed islet cell population, including ,45% BCD cells, for up to 16 population doublings, followed by a second stage of specific redifferentiation of BCD cells within the expanded islet cell population . RC treatment achieved a remarkably reproducible differentiation in cells from all human donors tested. These conditions induced a profound phenotypic change in the expanded cells, involving activation and shut-off of multiple genes. Lineage tracing suggests that the predominant source of newly-generated insulin-producing cells in these cultures is redifferentiation of BCD cells. These findings demonstrate for the first time that expanded dedifferentiated beta cells can be induced to redifferentiate in culture. Although we can not exclude a small contribution of other cell types to the C-pep + cells generated by RC treatment, the percent of label-positive cells among C-pep + cells is within the range of labelling efficiency, supporting the likelihood that the bulk of differentiation represents BCD cell redifferentiation. The mixed islet cell cultures may contain cells expanded from MSCs originally present in the islet preparation ; however we could not induce insulin expression with RC in non-BCD mesenchymal cell types, such as fibroblasts or Vorinostat manufacturer BM-MSCs. The specific redifferentiation capacity of BCD cells may be explained by a permissive epigenetic state . Thus, beta-cell genes may be poised for expression, however their lack of transcription may reflect an abnormal balance between transcription activators and repressors, and/or other chromatin modifications. Culture conditions in the redifferentiation medium may restore the proper balance without requirement for extensive epigenetic modifications. Upon transfer to RC, BCD cells are depleted of growth factors present in the serum of the expansion medium, resulting in growth arrest. However, growth arrest by itself is not sufficient for induction of redifferentiation in expanded islet cells, as suggested by overexpression of the cell cycle inhibitor p57, which induced growth arrest without differentiation .