Abstract
BackgroundMultiple 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.Principal FindingsIn 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.ConclusionsIn 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.
Highlights
In developing vertebrates, distinct types of fast and slow myofibers form during embryonic and fetal development
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
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
Summary
Distinct types of fast and slow myofibers form during embryonic and fetal development. Prdm is known to function in the differentiation of multiple non-myogenic cell lineages and is expressed in somites, though analyses of slow muscle formation have not been reported in Prdm1-null mice [4,5,6]. Because it was not known if Prdm was required for slow muscle formation in vertebrates other than teleost fish, we have examined Prdm expression and function in differentiating skeletal muscle cells from the chicken. Formation of the earliest slow myofibers in fin muscles requires expression of the zinc-finger transcriptional repressor Prdm ( known as Blimp). To further understand how the role of Prdm in early myogenesis may vary through evolution and during development, we have analyzed Prdm expression in the diverse types of myotubes that form in culture from somitic, embryonic, and fetal chicken myoblasts
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