Prdm1 (Blimp-1) and the expression of fast and slow myosin heavy chain isoforms during avian myogenesis in vitro.
BACKGROUND
Multiple types of fast and slow skeletal muscle fibers form during early embryogenesis in vertebrates. In zebrafish, formation of the earliest slow myofibers in fin muscles requires expression of the zinc-finger transcriptional repressor Prdm1 (also known as Blimp1). To further understand how the role of Prdm1 in early myogenesis may vary through evolution and during development, we have now analyzed Prdm1 expression in the diverse types of myotubes that form in culture from somitic, embryonic, and fetal chicken myoblasts.


RESULTS
In cultures of somitic, embryonic limb, and fetal limb chicken cells, we found that Prdm1 was expressed in all of the differentiated muscle cells that formed, including those that expressed only fast myosin heavy chain isoforms, as well as those that co-expressed both fast and slow myosin heavy chain isoforms. Prdm1 was also expressed in Pax7-positive myoblasts, as well as in non-myogenic cells in the cultures. Furthermore, though all differentiated cells in control somite cultures co-expressed fast and slow myosin heavy chains, antisense knockdown of Prdm1 expression inhibited the formation of these co-expressing cells in somite cultures.


CONCLUSIONS
In chicken myogenic cell cultures, Prdm1 was expressed in most Pax7-positive myoblasts and in all differentiated muscle cells, irrespective of the developmental stage of cell donor or the pattern of fast and slow myosin heavy chains expressed in the differentiated cells that were formed. Thus, Prdm1 was expressed in myogenic cells prior to terminal differentiation; and, after differentiation, Prdm1 expression was not limited to cells that expressed slow myosin heavy chain isoforms. In addition, Prdm1 appeared to be required for differentiation of the somitic myocytes, which are the earliest myocytes to form in the avian embryo.
Beermann
Mary Lou
ML
Neuromuscular Biology & Disease Group, Boston Biomedical Research Institute, Watertown, Massachusetts, United States of America.
Ardelt
Magdalena
M
Girgenrath
Mahasweta
M
Miller
Jeffrey Boone
JB
D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental; D024510:Muscle Development; D018656:Muscle Fibers, Fast-Twitch / Q000737:chemistry*; D018485:Muscle Fibers, Skeletal; D018657:Muscle Fibers, Slow-Twitch / Q000737:chemistry*; D032446:Myoblasts / Q000166:cytology; D018995:Myosin Heavy Chains / Q000737:chemistry / Q000235:genetics*; D020033:Protein Isoforms; D012097:Repressor Proteins / Q000502:physiology*
D020033:Protein Isoforms; D012097:Repressor Proteins; D018995:Myosin Heavy Chains