Biology Reference
In-Depth Information
Figure 20.2 Myogenic precursor cells derive from the dermomyotome and are not
released in c-Met or SF/HGF mutant embryos. Myogenic precursor cells are generated
from the dermomyotome (DM). From the dorsal edge, cells are delaminated that form the
myotome (MY). From the ventral edge, cells are released and migrate laterally into the
limb, and ventrally towards the anlage of the diaphragm (left). In c-Met or SF/HGF
mutant embryos, these cells retain their epithelial appearance and do not delaminate from
the ventral dermomyotome. SC: sclerotome
appears to be regulated by restricted expression of SF/HGF, although
additional signals could participate. Ectopic application of SF/HGF in
the chick embryo induces ectopic epithelial-mesenchymal transitions and
emigration of dermomyotomal cells (Brand-Saberi et al., 1996; Heymann et al.,
1996).
During migration, hypaxial muscle precursors continue to express c-Met,
but SF/HGF expression domains are highly dynamic. After migratory cells
have delaminated, SF/HGF transcripts can be observed along the routes and
at the targets of migrating muscle precursors. The characteristic expression
domains are maintained in the absence of the migrating cells, demonstrating
that the factor is produced by the mesenchyme and that it acts in a paracrine
manner on the migrating progenitors. In limb mesenchyme, SF/HGF
expression is controlled by signals that pattern the limb, which emanate
from the apical ectodermal ridge and the zone of polarizing activity. During
