We report a transient modulation of cell fate in fibroblasts briefly exposed to an extract derived from the rat insulin-producing P cell line, INS-1E. Primary fetal rat fibroblasts were reversibly permeabilized with Streptolysin O, incubated for 1 h in a 15,000g INS-1E nuclear and cytoplasmic extract, resealed, and cultured. A first marker of change in cell fate was a reduction of cell and nuclear size within days of exposure to extract such that in some instances the fibroblasts resembled INS-1E cells. Second, two beta cell transcripts, Pdx-1 and insulin, were detected in the fibroblasts for up to 4 weeks. Third, (pro)insulin labeling was detected in 5-30% of the cells for a period of 8-14 days after incubation in extract. These phenotypes were absent from fibroblasts exposed to heat-treated INS-1E extracts, a human fibroblast cell line-derived extract or buffer. The results indicate that the extract of an insulinoma-derived cell line can promote at least a transient modification of cell fate towards a beta cell phenotype in non-beta cells. Because they are easily accessible, cell extracts may represent a practical source of material for investigating the mechanisms of alteration of a nuclear and cellular program. (C) 2004 Elsevier Inc. All rights reserved.