Myogenic potential of chick limb bud mesenchyme in micromass culture

The myogenic potential of chick limb mesenchyme from stages 18-25 was assessed by micromass culture under conditions conductive to myogenesis, and was measured as the proportion of differentiated (muscle myosin-positive) mononucleated cells detected. It was found that similar myogenic potentials existed in mesenchyme from whole limbs between stages 18 and 19, but this potential was halved by stage 20. At stage 21, proximal mesenchyme showed significantly more myogenesis than distal mesenchyme, but this difference was abolished by stage 22. Thereafter, myogenesis was increasingly restricted from the distal mesenchyme, whilst the potential in more proximal regions did not significantly increase after stage 23. When the ratio between total limb myoblasts which differentiated on days 1 and 4 of culture was analysed, it was found that two distinct peaks existed at stages 20 and 23. The significance of these ratio peaks is unclear, but may be related to different proliferative potentials of the pre-myoblasts at these stages.