Ovoid fast muscle cells (white arrow) stretch out (green arrow) after a slow muscle cell (red) moves laterally (right) over them.
AMACHER/ELSEVIER
Fast-twitch muscle cells in zebrafish start off life as round blobs but must undergo anterio-posterior elongation to become functional myofibers. Henry and Amacher had noticed that this elongation process spreads in a medial-to-lateral wave, i.e., cells near the midline change shape first.
The authors first established that elongation required Hedgehog signaling. Transplantation experiments showed, however, that this effect was indirect. To restore fast-twitch elongation in a Hedgehog-signaling mutant, the critical ingredient was wild-type slow-twitch cells not wild-type fast-twitch cells.
In response to the Hedgehog signal, transplanted slow-twitch cells extended across the anterior–posterior width of a somite...
