First published online November 26, 2007
Development 134, 2401e (2007)
© The Company of Biologists Limited
Muscling in on myoblast biology
In Drosophila, the musculature consists of a stereotypic
arrangement of distinct muscles and its development involves two types of
myoblast: founder cells (FCs) and fusion-competent myoblasts (FCM). FCs, which
are generated from progenitor cells selected from promuscular cell clusters,
each fuse with several FCMs to form multinucleated myotubes that migrate under
the ectoderm to their target tendons, with which they form strong attachments.
This well-defined system is used to investigate many aspects of development,
including, as reported in this issue, the control of cell identity, the
mechanisms underlying cell fusion, and the control of cell migration and
adherence.
On p. 4347, Dubois
and colleagues reveal how the Drosophila embryonic Dorsal/Acute 3
(DA3) muscle lineage is specified. Sets of transcription factors are thought
to endow each FC with the capacity to seed the formation of a distinct muscle
type. To investigate this possibility, the researchers used the transcription
factor Collier (Col), which is expressed in the DA3 muscle and is required for
its formation, as a determinant and read-out of DA3 muscle identity. They
discover that separate sets of cis-regulatory elements activate col
in the DA3 promuscular cluster and in the FC progenitor cells and DA3
myofibre. In addition, they show that Col and Nautilus (which is also
essential for DA3 muscle formation) act together to ensure that all the nuclei
within the DA3 myofibre activate col and express the same
differentiation program. Overall, these results support the concept of a
combinatorial control of muscle identity.
On p. 4357,
Richardson and co-workers use live imaging to shed new light on the
involvement of cytoskeletal remodelling in myoblast fusion. They show that
F-actin accumulates at sites of myoblast fusion and that these actin foci
dissolve immediately before fusion occurs. Several mutations have been
identified in Drosophila that disrupt myoblast fusion, including
mutations in kette. Kette regulates SCAR/WAVE, an activator of
Arp2/3-dependent actin polymerization. The researchers report that in
kette mutant embryos, enlarged actin foci form that do not dissolve
normally. Actin foci dissolution and myoblast fusion also fail in
SCAR and Arp2/3 mutants. From their findings, the
researchers suggest that Kette-SCAR-Arp2/3-mediated actin polymerization
causes a reorganization of actin foci that is required for myoblast fusion and
that actin dynamics may also be critical for other cell-cell fusion
events.
Finally, on p.
4469, Estrada and colleagues describe how the transmembrane cell
adhesion protein Perdido (Perd), which is expressed in FCs and in growing
myotubes, interacts with the Glutamate receptor interacting protein (Grip) and
also with integrins to mediate myotube projection and attachment in
Drosophila embryos. Both of these processes, the researchers report,
are defective in perd loss-of-function mutants. In vitro, the Perd
intracellular domain interacts with a PDZ domain in Grip, another
muscle-expressed factor needed for myotube migration. Using a new,
whole-embryo RNA interference assay, the researchers also show that
perd interacts genetically with Grip and with multiple
edematous wings, which encodes one subunit of the 
PS1-βPS
integrin that is expressed in tendon cells. These results provide novel
insights into how Perd regulates myotube migration and attachment and indicate
how integrins function during these processes.
Related articles in Development:
- collier transcription in a single Drosophila muscle lineage: the combinatorial control of muscle identity
- Laurence Dubois, Jonathan Enriquez, Virginie Daburon, Fabien Crozet, Gaelle Lebreton, Michèle Crozatier, and Alain Vincent
Development 2007 134: 4347-4355.
[Abstract]
[Full Text]
- SCAR/WAVE and Arp2/3 are crucial for cytoskeletal remodeling at the site of myoblast fusion
- Brian E. Richardson, Karen Beckett, Scott J. Nowak, and Mary K. Baylies
Development 2007 134: 4357-4367.
[Abstract]
[Full Text]
- The transmembrane protein Perdido interacts with Grip and integrins to mediate myotube projection and attachment in the Drosophila embryo
- Beatriz Estrada, Stephen S. Gisselbrecht, and Alan M. Michelson
Development 2007 134: 4469-4478.
[Abstract]
[Full Text]
