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YC2.1 was expressed transgenically in Caenorhabditis elegans pharyngeal
muscle under the control of the pharyngeal-specific myo-2 promoter ( Kerr
et al. , 2000 ) and tracked calcium changes during pharyngeal pumping;
YC3.1 tracked temporal changes more faithfully than YC2.1, being the
faster sensor, but YC2.1 tracked calcium changes to basal level more faith-
fully than YC3.1, as might be expected from its lower K 0 d .Expressionof
YC2.12 in C. elegans touch neurons under the control of the mec-4 promot-
er identified a role for specific ion channels in the touch response ( Suzuki
et al. , 2003 ).
The UAS/Gal4 tissue-specific expression system was used to express YC2.1 in a
subset of the antennal lobe projection neurones of Drosophila in order to study
odorant responses in the antennal lobe and mushroom body calyx in vivo
( Diegelmann et al. , 2002; Fiala et al. , 2002 ). Odorant-specific patterns of neuronal
excitation were seen in both the antennal lobe and the calyx. In the former, the
EYFP/ECFP emission ratio changes were 1.23
0.23% (mean and sem) and in the
latter 0.6
0.06%. In the antennal lobe, the changes in sensor signal were observed
in spatially restricted regions of around 10-30 m m diameter, the size of individual
glomeruli. These very small changes were nonetheless reproducible, with distinct
and reproducible patterns of activity from fly to fly associated with di
V
erent
odorants.
The same UAS/Gal 4 technology was used to express YC2 in neurones of
larval Drosophila ( Rei
et al. ,2002 ) to the evolution of calcium signaling in
presynaptic terminals innervating larval muscle. A 28% emission ratio change
was measured in vivo during spike train stimulation of the neuromuscular junc-
tion and signals of this magnitude could be resolved in single synaptic boutons;
there were no detectable di
V
erences in neuromuscular junction physiology
between wild-type and transgenic larvae. This study illustrates the point that
targeted expression of genetically encoded sensors in individual neurones is for
some applications superior to the use of low molecular mass synthetic calcium
indicators, as the specificity of expression more than compensates for the loss of
brightness.
In a similarly mature use of YC2.1 sensor technology coupled to UAS/Gal4
transgenic expression, neuronal calcium measurement coupled with electrophysi-
ology was used to identify thermosensory neurones in the larval nervous system
in vivo ( Liu et al. , 2003 ). Changes in emission ratio of 10-50% were associated with
heating and cooling. A functional map of thermosensory neurones was generated
and it was found that neurones with di
V
V
erent temperature responses were anato-
mically segregated.
YC2.1 was also used in zebrafish to record the behavior of Rohon-Beard (RB)
neurones during the fish's escape response ( Higashijima et al. , 2003 ). This careful
study started with transient expression of the YC2.1 transgene in the RB neurones to
show proof of principle before generating transgenic lines in which the calcium signals
in the RB neurons could be correlated with the escape response in conscious fish.
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