Local signals in the chick limb bud can override myoblast lineage commitment: induction of slow myosin heavy chain in fast myoblasts

Patterning of fast and slow muscle fibres in limbs is regulated by signals from non-muscle cells. Myoblast lineage has, however, also been implicated in fibre type patterning. Here we test a founder cell hypothesis for the ro le of myoblast lineage, by implanting characterized fast and slow mouse myo blast clones into chick limb buds. In culture, late foetal mouse myoblast c lones are committed to a probability (range 0-0.92) of slow myosin heavy ch ain (MyHC) expression. In contrast, when implanted into chick limbs, fast m ouse myoblast clones express myosin characteristic of their new environment , without fusion to chick muscle cells and in the absence of innervation. T herefore, local signals exist within the chick limb bud during primary myog enesis that can override intrinsic commitment of at least some myoblasts, a nd induce slow MyHC. (C) 1999 Elsevier Science Ireland Ltd. All rights rese rved.