A study on skeletal myogenic cell movement in the developing avian limb bud

Spatial and temporal contribution of somitic myoblasts to avian hind limb muscles

Skeletal muscles of the avian limb are derived from mononucleated myogenic precursor cells (myoblasts) that migrate into the somatopleural mesoderm of the developing limb bud from the ventrolateral dermomyotome of limb adjacent somites. In the present study, we utilized replication-deficient lacZ-encoding retroviruses to elucidate the source of myoblasts for all hind limb muscles in the chick and define the distinct patterns of myoblast distribution within the limb. We also examined, using the same marker, whether the time of migration from the somites into the limb dictates the spatial contribution the myoblasts make to the developing musculature, particularly in relation to the proximodistal and dorsovental axes. Finally, we used these investigations to examine whether the precursors of both primary and secondary myotubes are derived from somitic mesoderm, a presumption, which up until now, has not been demonstrated in vivo. Overall, the results of our studies demonstrate that individual somites have a selective spatial pattern of participation in the development of the avian hind limb musculature and contribute to both primary and secondary myotubes. We also show that both early and later migrating myoblasts can contribute fully to the formation of the appendicular muscles.

Hepatocyte growth factor stimulates chemotactic response in mouse embryonic limb myogenic cells in vitro

In this study we investigate the influence of Hepatocyte Growth Factor (HGF) on the motility of embryonic forelimb myoblasts. Using Blindwell chemotactic chambers, it was found that HGF at concentrations of 1-50 ng/ml dramatically enhanced the ability of myogenic cells to migrate. This stimulatory effect was elicited in a dose-dependent fashion and the effect was reversed with the addition of HGF neutralizing antibodies. A checkerboard analysis was performed and it revealed that HGF's effect on limb myoblast motility was through both chemokinesis and chemotaxis. HGF was also examined for its ability to stimulate myogenic cell proliferation, using MF20 antibody as the myogenic marker. At all concentrations tested, HGF did not stimulate an overall increase in the numbers of MF20-positive myoblasts in culture. To examine the chemokinetic effect of HGF on cell migration in the limb, cells were isolated from the proximal regions of the limb (areas rich in myogenic cells), exposed to HGF, labeled with DiI and transplanted into 11.5 day mouse forelimbs. After 36 h of culture, it was found that DiI-labeled limb cells, pretreated with HGF, migrated significantly further in the limb than labeled cells that have not been exposed to HGF. The chemotactic effect of HGF was also investigated by implanting beads loaded with and without HGF into the 11.5 day limb. Proximal to the beads, DiI-labeled limb cells were also transplanted. It was found that HGF was able to chemotactically attract and direct the migration of DiI-labeled limb cells. Immunohistological staining was performed with HGF antibodies to determine the distribution of HGF in the 11.5 day mouse forelimb. It was found that HGF was strongly expressed by the apical ectodermal ridge (AER), the ectoderm and the mesenchyme directly beneath the AER. Positive staining was also obtained for the myogenic regions. However, the pattern was heterogeneous--punctuated with myogenic cells expressing and not expressing HGF.

Fibroblast growth factors 2 and 4 stimulate migration of mouse embryonic limb myogenic cells

Fibroblast growth factors (FGFs) are believed to be vital for limb outgrowth and patterning during embryonic development. Although the effect of FGFs on the formation of the skeletal elements has been studied in detail, their effect on the development of the limb musculature is still uncertain. In this study, we used Blindwell chemotactic chambers to examine the effect of FGF-2 and FGF-4 on the motility of myogenic cells obtained from the proximal region of the day 11.5 mouse forelimbs. The limb myogenic cells were found to be chemotactically attracted to FGF-2 and FGF-4 at 10-50 ng/ml. Both FGFs increased myogenic cell migration in a dose-dependent manner, with maximal responses attained at 1-50 ng/ml for FGF-2 and at 10 ng/ml for FGF-4; however, FGF-2 was found to be a more potent chemoattractant than FGF-4. It was possible to inhibit the myogenic cells' response to FGF-2 and FGF-4 by the addition of the appropriate neutralizing antibody. The effects of FGF-2 on cell migration were further investigated by loading this cytokine into Affi-Gel blue beads and transplanting them into day 11.5 forelimb buds. The results showed that FGF-2 attracted DiI-labelled proximal cells to migrate toward the implanted beads and that the migration was more extensive than that observed in the absence of FGF-2. A checkerboard assay was performed in which various concentrations of FGF-2 and FGF-4 were introduced to both the upper and lower wells of the Blindwell chambers. The results indicated that both FGF isoforms can stimulate chemokinesis as well as chemotaxis in myogenic cells. In addition, the effect of FGF-2 at 0.1-10 ng/ml stimulated a significant increase in the number of myocytes expressing sarcomeric myosin on examination after 48 hr in culture, but the effect of FGF-4 was negligible at all concentrations analyzed; however, both FGF-2 and FGF-4 inhibited myocyte fusion compared with the spontaneous fusion observed in control cultures. Finally, we used in situ hybridization and immunohistochemical techniques to determine the distribution of myogenic cells and FGF-2 protein in the day 11.5 mouse forelimbs.

Translocation of fibronectin-coated and uncoated latex beads in avian embryonic limb buds

Latex beads were implanted into the chick wing bud to determine whether parameters other than active movement, for example matrix-driven translocation and growth of the limb bud, were responsible for the extensive re-allocation of myogenic cells that occurs during limb development. Latex beads were implanted into nine stage 20-24 Hamburger and Hamilton (H.H.) wing buds, and were allowed to develop for 3 days before examination. In all cases, it was found that most of the latex beads (86.57% +/- 11.4%) were confined to the implantation site. A small percentage of beads was observed in the connective and myogenic regions proximal and distal to the graft side. In general the displacement of these beads was relatively short, although in one specimen a few beads were translocated to regions as far as the autopod. The surface of the latex beads was also coated with fibronectin prior to transplantation, to ascertain whether the extracellular matrix can influence the translocation of beads within the limb bud. Ten specimens were examined, and as for uncoated latex beads, most of the fibronectin-coated beads (87.14% +/- 11.67%) were contained within the transplantation site. Again a small percentage of beads was found in the connective and myogenic but not in the chondrogenic tissues proximal and distal to the graft side. In one specimen fibronectin-coated beads were translocated to regions in the autopod, but in general, bead displacement was relatively short. In sum, latex beads can not move to any great extent within the limb bud, and the coating of these beads with fibronectin did not influence bead translocation.