eFGF and its mode of action in the community effect during Xenopus myogenesis

The community effect is an interaction among a group of many nearby precurs or cells, necessary for them to maintain tissue-specific gene expression an d differentiate co-ordinately. During Xenopus myogenesis, the muscle precur sor cells must be in group contact throughout gastrulation in order to deve lop into terminally differentiated muscle. The molecular basis of this comm unity interaction has not to date been elucidated. We have developed an ass ay for testing potential community factors, in which isolated muscle precur sor cells are treated with a candidate protein and cultured in dispersion. We have tested a number of candidate factors and we find that only eFGF pro tein is able to mediate a community effect, stimulating stable muscle-speci fic gene expression in demonstrably single muscle precursor cells. In contr ast, Xwnt8, bFGF, BMP4 and TGF beta2 do not show this capacity. We show tha t eFGF is expressed in the muscle precursor cells at the right time to medi ate the community effect. Moreover, the time when the muscle precursor cell s are sensitive to eFGF corresponds to the period of the endogenous communi ty effect. Finally, we demonstrate that FGF signalling is essential for end ogenous community interactions. We conclude that eFGF is likely to mediate the community effect in Xenopus myogenesis.