Myoblasts transferred to the limbs of embryos are committed to specific fibre fates

Abstract

In the limb bud of the 5-day-old avian embryo, when primary muscle fibre formation is beginning and before specific muscles appear, differences in the expression of fast and slow myosin heavy chain genes can be detected among primary fibres of the premuscle masses. Myoblasts that form colonies of fibres of specific types can be isolated from these limb buds. To assess the role of myoblast commitment in specifying fibre types during embryonic development, we cloned myoblasts of specific types from embryonic and adult muscles, transfected them with a reporter gene, and transferred them into developing limb buds. After transfer, cloned myoblasts formed fibres in the limb with the same patterns of myosin heavy chain gene expression as the fibres they formed in cell culture. These results demonstrate that initial skeletal muscle fibre type diversity during avian limb development can originate, in part, from the commitment of distinct myoblast types to the formation of specific fibre types.

E-Box Sites and a Proximal Regulatory Region of the Muscle Creatine Kinase Gene Differentially Regulate Expression in Diverse Skeletal Muscles and Cardiac Muscle of Transgenic Mice

“…It is not yet understood how muscle fiber phenotypes develop or are maintained (15,43,53,60). Nevertheless, both developmental cues and extrinsic signals affect muscle fiber type and gene expression (3,14,19,22,46), and genes, including the myosin and troponin families, human aldolase A, and muscle-specific transcription factors, exhibit differential expression in fast and slow muscles (4,11,23,28,36,52,55,57,58,68). The skeletal muscles we examined contain different compositions of fast-twitch glycolytic fibers (expressing MyHC IIb), fast-twitch oxidative-glycolytic fibers (expressing either MyHC IIa or IIx), and slow-twitch oxidative fibers (expressing ␤/slow MyHC) (24,53,60).…”

“…CAT enzyme standards were analyzed in parallel to ensure that activities of diluted extracts were within the linear range of the assay. Counts per minute (cpm) from [acetyl- 14 C]chloramphenicol were converted to microunits of CAT activity, where 1 U of CAT activity is defined as the amount sufficient to acetylate 1 mol of chloramphenicol per min at 37ЊC (61). Samples which exhibited less than twice the CAT assay background counts per minute (40 to 60 cpm) are indicated as 0 U of CAT per mg of protein.…”

Localisation of transforming growth factor beta 1 in developing muscles: Implications for connective tissue and fiber type pattern formation

“…In the embryo, the intrinsic characteristics of fibers dominate and the pattern of fiber types within embryonic muscles is largely unchanged by the removal of neural influences (Butler et al, 1982;Phillips and Bennett, 1984). Myoblasts, like myotubes, are heterogeneous and are committed to form fibers of a particular type (Stockdale, 1992;Dimario et al, 1993) and this had led to the widely held belief that the intrinsic characteristics of fibers are determined by the myoblasts from which they were initially formed.…”

Sox6 is required for normal fiber type differentiation of fetal skeletal muscle in mice

“…To delineate the two, myoblast transplantation experiments have been performed by several laboratories. In chickenquail transplantation experiments, it was shown that the embryonic myoblasts (which form primary myotubes) are committed to a specific fiber type independent of the environment (DiMario et al, 1993;Nikovits et al, 2001). A similar result was obtained by limb bud transplantation experiments showing that myoblasts migrating early (embryonic myoblasts) and late (fetal myoblasts) into limb buds have mainly slow and fast fiber fate, respectively (Van Swearingen and Lance-Jones, 1995).…”