We previously presented evidence that proliferative human islet precursor cells may be derived in vitro from adult islets by epithelial-to-mesenchymal transition (EMT) and show here that similar fibroblast-like cells can be derived from mouse islets. These mouse cell populations exhibited changes in gene expression consistent with EMT. Both C-peptide and insulin mRNAs were undetectable in expanded cultures of mouse islet-derived precursor cells (mIPCs). After expansion, mIPCs could be induced to migrate into clusters and differentiate into hormone-expressing islet-like aggregates. Although early morphological changes suggesting EMT were observed by time-lapse microscopy when green fluorescent protein-labeled beta cells were placed in culture, the expanded precursor cell population was not fluorescent. Using two mouse models in which beta cells were permanently made either to express alkaline phosphatase or to have a deleted M(3) muscarinic receptor, we provide evidence that mIPCs in long term culture are not derived from beta cells.