Seminar for PhD students - Max-Planck-Institut für biophysikalische ...

Genetic screen for modifiers of muscular dystrophy in
Drosophila melanogaster
Muscular dystrophy (MD) is a general
term that describes a group of inherited and
gradually progressing myogenic disorders
that are frequently associated with cardiomyopathy
and brain disorders. Genetically
the pattern of inheritance can be X-linked
recessive as in Duchenne or Becker muscular
dystrophy (DMD/BMD), autosomal
dominant as in limb-girdle muscular dystrophy
type 1 (LGMD type 1), or autosomal
recessive as in limb-girdle muscular dystrophy
type 2 (LGMD type 2) (Campbell,
1995; Straub, Campbell, 1997). DMD is
a severe progressive muscle-wasting
disease affecting approximately 1 out of
3500 males (Blake et al, 2002).
One of the most important advances
in understanding the molecular genetics
of neuromuscular diseases has been
the cloning of the gene encoding dystrophin,
the protein absent in muscle of DMD
patients. In the last few years the role of
dystrophin in skeletal muscle has been
studied, and several dystrophin-associated
proteins that form a Dystrophin-Glyco-
protein Complex (DGC) have been identified.
The DGC consists of dystrophin,
the dystroglycans, the sarcoglycans,
sarcospan, the syntrophins and dystrobrevin
(Durbeej and Campbell, 2002). The
DGC components are now being characterized
and evidence is beginning to indicate
that proteins of this complex may
be responsible for other forms of muscular
dystrophy (Campbell, 1995).
Unfortunately all known cases of MD
belong to the category of incurable, therefore
further studying of the DGC function is
very important. A number of animal models
have been established for DMD, but
severe muscular dystrophy in the absence
of dystrophin alone has only been observed
in dogs (reviewed in Collins and Morgan,
2003). Mice and C.elegans exhibit muscle
degeneration in the absence of dystrophin
when also lacking myoD (Gieseler
et al., 2000; Megeney et al., 1996), a
gene required for muscle regeneration.
This fact makes it difficult to study the
mechanisms of MD utilizing such models,
Doktorandenseminar - Seminar for PhD students
Organizing team: W. Fischle, G. Groenhof, C. Höbartner, S. Jakobs, A. Lange
Summary of the “Seminar for PhD Students“ by Mariya Kucherenko,
Max Planck Research Group of Gene expression and signaling, 12.8.2009
hence development of a new remarkably
good model for genetic manipulations
remains an open task.
Drosophila melanogaster was used as
a model for human diseases previously.
Characterization of the fly DGC shows
that the fruit fly retains all essential components
of the DGC, but with substantially
less diversity (Greener and Roberts, 2000).
Furthermore, regions and domains known
to mediate interactions between members
of the complex are highly conserved between
human and fly, suggesting that the
overall structure of the complex is identical
(Neuman et al, 2005). Recently, a
model for muscular dystrophy caused by
Dystrophin (Dys) and Dystroglycan (Dg)
deficiency was established in Drosophila
melanogaster and phenotypes similar with
human neuromuscular diseases were
described (Shcherbata et al, 2007). Mutations
in Drosophila Dystrophin and Dystroglycan
genes cause shortened lifespan and
reduced mobility as a result of age dependent
muscle degeneration. In addition, the
(+) inretaction; (-) no interaction; (En) enhancement.
Seite 20
reduction of Dys and Dg leads to defects in
eye development as manifested by altered
photoreceptor axon path-finding.
To review new components that interact
with the DGC or regulate its function we
used a Drosophila melanogaster model for
muscular dystrophy and performed genetic
interaction screens to identify dominant
modifiers of Dg and Dys related mutant
phenotypes. In the primary large scale
screen we looked for modifications of
an easily score-able phenotype such as
alterations in the posterior crossvein.
Using this screening strategy we have found
38 modifiers that belong to different functional
groups: genes involved in muscle
function, neuronal/cell migration and
motor function as well as cytoskeletal
components and components of the TGFbeta,
EGFR and Notch signaling pathways
(Kucherenko et al, 2008).
In order to shed light on the mechanisms
of muscle degeneration caused by Dys and
Dg down regulation a secondary screen
in muscle tissue was performed (Figure
Table 1. Modifiers of muscle degeneration phenotype caused by reduced level of Dys and Dg.