Biomedical Engineering Reference
In-Depth Information
Keywords
Drosophila
• GAL4/UAS system • Genetically encoded Ca
2+
indicator
(GECI) • Imaging
7.1
Introduction
Drosophila melanogaster
is one of the most important model organisms for vari-
ous fi elds of biological research, such as genetics, developmental biology, or neu-
roscience. The fruit fl y is easy to breed, and it produces much offspring in short
generation cycles. Under ideal conditions, the development from egg to adult takes
only ca. 10 days at 25 °C. Moreover, the fruit fl y exhibits a wide array of stereo-
typed and nonstereotyped, fl exible behaviors, covering simple refl exes such as
phototaxis (Benzer
1967
) or chemotaxis (Vosshall and Stocker
2007
); circadian
behavior and sleep (Hendricks et al.
2000
); more complex behavioral patterns,
e.g., courtship (von Philipsborn et al.
2011
) or aggression (Dankert et al.
2009
;
Hoyer et al.
2008
); and behavioral plasticity, e.g., olfactory learning and memory
formation (Fiala
2007
).
The brain of the fruit fl y, which controls these behaviors, is composed of ca.
100,000 neurons (Chiang et al.
2011
; Shimada et al.
2005
). As a general principle,
their cell bodies are distributed at the outer surface of the brain, whereas their pro-
cesses innervate the interior side of the brain and form the synaptic neuropils.
Decades of research have led to a fairly good description of the neuronal structures
and connectivities within the
Drosophila
brain. A recent construction of a meso-
scopic map of the fruit fl y brain has, for example, suggested that the
Drosophila
brain consists of 41 local processing units, six hubs, and 58 tracts (Chiang et al.
2011
). It is obvious that the numbers of nerve cells and structurally identifi able
brain regions are much smaller than those of higher vertebrates, which facilitates of
course the analysis of circuits underlying behavior. However, the most important
advantage of
Drosophila
when compared with other organisms relies on sophisti-
cated gene-expression systems that can be used, for example, to monitor and manip-
ulate neural activity in vivo.
Genetic germline transformation techniques based on the
P
element transposon
(Spradling and Rubin
1982
) have initially been used to identify and disrupt genes
and their regulatory elements. But
P
elements carrying regulatory elements are also
used to induce gene expression, e.g., of fl uorescent sensor proteins, in a cell type-
specifi c spatiotemporal pattern (Duffy
2002
; Venken et al.
2011
). The combination
of a wide array of behavioral paradigms, a relatively small brain, and sophisticated
expression systems with new tools to monitor and manipulate neural activity turns
Drosophila
into an excellent model system to study the complexity of a brain in
detail. This chapter will provide a brief introduction in
Drosophila
genetics, a sum-
mary of the available genetic tools to visualize neural activity, and examples of their
applications in
Drosophila
neurobiology.
