Investigating insulin

Previous studies have shown that adult or embryonic stem (ES) cells can be differentiated in vitro to form insulin-containing, islet-like structures. In the January 17 Science, Jayaraj Rajagopal and colleagues add a note of caution to the interpretation of such insulin-staining experiments (Science, 299:363, January 17, 2003).

ES cells could be differentiated into clusters of cells that are recognised by an antibody against insulin, but Rajagopal et al. could not detect any insulin mRNA. In addition they observed that ES cells expressing green fluorescence protein from an insulin promoter did not glow green. Insulin staining was lost when ES cells were cultured in insulin-deficient media. Direct evidence for insulin-uptake was provided by using a fluorescently-conjugated insulin in the media. Thus, insulin immunoreactivity is insufficient evidence for beta cell differentiation.