INVESTIGATION OF THE ROLE OF INOSITOL AND THE PHOSPHATIDYLINOSITOL SIGNAL-TRANSDUCTION SYSTEM IN MOUSE EMBRYONIC STEM-CELLS

The aims of this study were to investigate in mouse embryonic stem cel ls (1) the requirement for myo-inositol for cell proliferation, (2) th e incorporation of inositol into the phosphoinositides and inositol ph osphates of the phosphatidylinositol (PtdIns) signal transduction syst em and (3) the effect of serum growth factors on PtdIns turnover. Exog enous myo-inositol was not essential for embryonic stem cell prolifera tion. Lithium, an inhibitor of endogenous inositol recycling, inhibite d embryonic stem cell proliferation but this effect was not reversible by the addition of high concentrations of exogenous inositol. [H-3]in ositol was incorporated into the phosphoinositides, PtdIns, PtdIns4P a nd PtdIns(4,5)P-2 in similar proportions as reported for other cells. [H-3]inositol was also incorporated into a fourth lipid, tentatively i dentified as an inositolglycan. [H-3]inositol was also incorporated in to a number of inositol phosphates, with the greatest amount of incorp oration after 24 h into an inositol pentakisphosphate. After serum sta rvation for 24 h, the addition of 10% whole or dialysed serum for 2 or 20 min increased (P < 0.05) incorporation into inositol tris- and tet rakisphosphates. These results demonstrate the presence of PtdIns syst em components in embryonic stem cells and increased PtdIns turnover in response to serum growth factors.