We report the differentiation of human adipose tissue stem cells (ATSCs) to take on cardiomyocyte properties following transient exposure to a rat cardiomyocyte extract. Reversibly permeabilized ATSCs were incubated for 1 h in a nuclear and cytoplasmic extract of rat cardiomyocytes, resealed with CaCl2, and cultured. Three weeks after exposure to extract, ATSCs expressed several cardiomyocyte markers including sarcomeric alpha-actinin, desmin, and cardiac troponin 1, and displayed targeted expression of the gap junction protein connexin 43. Formation of binucleated and striated cells, and spontaneous beating in culture were also observed. A low proportion of intact ATSCs exposed to the extract also showed signs of alpha-actinin and connexin 43 expression. Additional evidence of differentiation was provided by induction of expression of nuclear lamin A/C, a marker of terminally differentiated cells, and a remarkable increase in cell cycle length. Together with our previous data [Nat. Biotechnol 20 (2002) 460], this study suggests that alteration of cell fate using cellular extracts may be applied to multiple cell types. Cell extracts may also prove useful for investigating the molecular mechanisms of stem cell differentiation. (C) 2003 Elsevier Inc. All rights reserved.