Gene targeting the myf‐5 locus with nlacZ reveals expression of this myogenic factor in mature skeletal muscle fibres as well as early embryonic muscle

Abstract

We have introduced the nlacZ reporter gene into the locus of the myogenic factor gene myf-5 by homologous recombination in embryonic stem (ES) cells. Targeted ES clones were injected into precompaction morula, and the beta-galactosidase expression pattern was monitored. These mice permit the sensitive visualization of myf-5 expression throughout the embryo, and provide a standard for comparing it with that seen with different myf-5/nlacZ transgenes. Thus, in a comparison using ES cells in chimaeric embryos containing the targeted or randomly integrated myf-5/nlacZ construct, we demonstrate that 5.5 kbp of myf-5 upstream flanking sequence including exon1 and most of intron1 directs some skeletal muscle expression, but this is neither qualitatively nor quantitatively equivalent to that of the endogenous gene. Myf-5 is expressed early, before terminal myogenesis takes place in the medial half of the somite, and subsequently it is a major myogenic factor as skeletal muscle forms. All skeletal muscle shows beta-galactosidase activity, even after birth, indicating that myf-5 expression is not confined to primary myotubes, which are derived from embryonic myoblasts, but is also present in muscles containing different adult fibre types. The presence of myf-5 transcripts from the endogenous gene in older muscle was confirmed by in situ hybridization. These results suggest that the myf-5 gene is not activated in only a subset of muscle cells and are consistent with the results on the MyoD knockout mice.

Pericytes resident in postnatal skeletal muscle differentiate into muscle fibres and generate satellite cells

“…1m); however, AP was never detected in Pax7 + or MyoD + satellite cells at any time examined; an example at P7 is shown in Supplementary Figure S1e,f, respectively. These results were confirmed by enzymatic staining for AP on muscles sections from the Myf5 nlacZ/ + mouse (expressing nuclear β-gal only in Myf5 + cells 19 ) (Fig. 1n), even after cardiotoxin-induced regeneration ( Supplementary Fig.…”

Extracellular matrix remodeling accompanies axial muscle development and morphogenesis in the mouse

“…We suggest that fibronectin may guide the reorientation of the myotomal myocytes whereas tenascin is in a position to play a tendon-and muscle connective tissue-like role (Deries et al, 2010;Mathew et al, 2011 Two basement membranes are essential during the first stages of myogenesis in the mouse: one lines the basal side of the dermomyotome and plays a significant role in preventing muscle progenitors from entering the myogenic program too early (Bajanca et al, 2006). The other is the basement membrane covering the medio-ventral surface of the myotome, which separates it from the sclerotome and keeps myogenic cells from getting dispersed into the sclerotome (Tosney et al, 1994;Tajbakhsh et al, 1996;Bajanca et al, 2006;Anderson et al, 2009). It should also be noted that both are distinct from the basement membrane that later surrounds the maturing muscle fibers (Cachaço et al, 2005).…”

Bone Marrow-Derived Hematopoietic Cells Undergo Myogenic Differentiation Following a Pax-7 Independent Pathway

“…Myf5 nlacZ/þ mice [19] were kindly provided by Dr. Tajbakhsh and C57/ MlacZ mice were previously described [2]. To obtain EGFP transgenic mice in which the nuclearly localized b-gal is under the control of the MLC3F or Myf5 promoter, C57BL/6-Tg(ACTbEGFP)1Osb/J heterozygotes were bred with C57/ MlacZ homozygotes or Myf5 nlacZ/þ mice, respectively.…”

“…This makes it an excellent marker of myogenic specification. We used a knock-in mouse strain, which express the nuclearly localized b-galactosidase (b-gal) under the control of the Myf5 promoter [19]. BM cells derived from the Myf5 nlacZ/þ mice were cocultured with WT unlabeled primary myoblasts at a ratio of 1/1 in culture conditions allowing myoblast proliferation.…”