Developmental myosin heavy chain progression in avian type IIB muscle fibres

Summary Myosin heavy chain species were investigated during development in avian pectoralis major muscle (type IIB fibres) by high resolution anion-exchange chromatography of the myosin head region, subfragment-1. At 15 daysin ovo four distinct fast-type heavy chain species, I, II, III and IV, in order of elution, were identified. By 19 daysin ovo, form IV had become predominant and remained the major species through 3-days post-hatch. This form has been named theperihatch form. Between 3 and 5 days post-hatch, a second massive change occurred such that by 5 days post-hatch a new species, V, apparent at 19 daysin ovo in small amounts, dominated and at 8 days post-hatch was the only heavy chain species present. Form V, which corresponds to that previously identified as theposthatch form, continued as the major species through 20 days post-hatch and was replaced slowly by the adult form. N-terminal sequencing of CNBr peptides from three subfragment-1 heavy chain species, the peri-hatch (form IV), the post-hatch (form V) and adult, revealed differences in amino acid sequence consistent with the three being products of different genes. These results confirm and extend recent reports of complexity in fast heavy chain expression prior to hatching in the chicken (Hofmannet al., 1988; Van Horn & Crow, 1989).