Myoblast motility.

The cytoskeleton of myoblasts (shown by scanning electron microscopy above) is dense.  In aligned myoblasts, just prior to fusion, most of the actin is found just underneath the plasma membrane where it interacts with non-muscle myosin to help produce the elongated shape of these aligned myoblasts (as shown in the picture below).

We decorated the actin with myosin subfragment 1, which gives an arrowhead appearance to the actin, and shows how the actin is organised (see picture opposite) just underneath the membrane in aligned cells, and found that it has a random orientation.

(see Swailes et al., 2004 and 2006).

The functions of different unconventional myosins in myoblasts:

Myoblasts express at least 5 different classes of myosin; 1,2,5,9 and 10 (Wells et al., 1997). Their expression levels decline when the myoblasts differentiate into myotubes.

Click here to see a short movie of myoblasts crawling over a surface, using the DRIMAPS technique. A record is taken every minute. This movie shows all the records for 6 hours. DRIMAPS (Digitally Recorded Interference Microscopy with Automatic Phase Shifting, developed by Dr G.A. Dunn and D. Zicha) is a powerful technique for analysing cell locomotion. The false colour image is related to the dry mass distribution of the cell (see Peckham et al., 1999, 2001). This technique allows us to calculate the dry mass distribution of living cells as they move over a surface. The resultant images can be used to calculate a wide range of parameters such as speed, rates of protrusion and retraction, polarity, etc. Using this method we showed that cells overexpressing b-actin moved twice as fast as wild type cells when they were not well spread (Peckham et al., 2001). Cells overexpressing a mutant isoform of b-actin, that polymerises less well, also moved faster. Inhibition of acto-myosin contractility using BDM, abolished the extra motility. This suggests that the extra motility is not due to additional actin polymerisation, but depends on myosin function.

see comments: Nature Science Update, Trends in Cell Biology, 11, (7) p281