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Of Macrophages and Muscle

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Science  06 Jun 2003:
Vol. 300, Issue 5625, pp. 1479
DOI: 10.1126/science.300.5625.1479c

One function of the cytokine interleukin 4 (IL-4) when released by T cells is to stimulate macrophage fusion. Horsley et al. show that IL-4 is also a fusion-stimulating signal for nascent myotubes and that it promotes myotube growth by enhancing fusion of myoblasts to existing myotubes. The c2 isoform of the transcription factor NFAT (nuclear factor of activated T cells) is activated in nascent myotubes just after fusion. In myoblasts lacking NFATc2, myotube size and nuclei number could be restored to wild-type levels by application of IL-4. Furthermore, IL-4 expression and secretion were increased during the period after initial myotube formation and were absent in the NFATc2-deficient myotube cultures. Finally, in a coculture fusion assay, the myotube-released IL-4 stimulated the IL-4 receptor-expressing myoblasts to fuse with existing myotubes.—NG

Cell 113, 483 (2003).

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