The development of differentiated cells from undifferentiated progenitor cells is one of the central tenets of developmental biology. However, under conditions of tissue morphogenesis, regeneration, and cancer, this process of development is reversed and fully differentiated cells transition to an undifferentiated phenotype. Here we present evidence that the zinc-finger transcription factor Snail modulates this transition in differentiated pancreatic endocrine cell lines. During passage and growth of these cells lines, Snail expression is induced in a subset of cells within the culture, concomitant with a decrease in insulin and/or glucagon expression within. As the cells cluster and exit the cell division cycle, nuclear levels of Snail are reduced and hormone expression is resumed. Snail represses proinsulin and proglucagon gene transcription and reduction of Snail levels by siRNA treatment increases proinsulin gene expression. We propose that Snail modulates the dynamic balance between differentiated and dedifferentiated cells allowing their migration and proliferation. These findings may be relevant to providing approaches for the enhancement of cell growth in individuals with diabetes mellitus.