Biology Reference
In-Depth Information
one
Drosophila
species, insert it into a
P
-element vector, and introduce the
exogenous gene into mutant strains of
D. melanogaster
to confirm that the
putative gene does, in fact, code for the behavior of interest. Cloned genes from
Drosophila
can, in some cases, be used as probes to identify genes from other
arthropods, which then can be sequenced and compared. The availability of the
complete genome of
D. melanogaster
, and of other insects, allows analyses of
behavior that could not be conducted previously.
11.5.1 The Photoperiodic Clock
The potential that molecular genetics offers was first exemplified by analy-
ses conducted using the
period
+
, and other clock genes, of
D. melanogaster
(
Table 11.2
). Most insects exhibit particular behaviors at a specific time of the
day, which are due to the action of a
circadian clock
that allows the insect to
Table 11.2: Some Genes Involved in the Circadian Clock of
Drosophila melanogaster.
Gene
(abbreviation)
Mutant phenotype(s)
Function(s)
period
+
(
per
+
)
Short-period, long-period
and arrhythmic flies
Affects locomotion,
eclosion, courtship
rhythms
Negative transcription element;
per
+
mRNA levels rise late
in the day
Activated by the heterodimer of the CLOCK and CYCLE
proteins
PER proteins feed back negatively on their own transcription
PER contains a protein dimerization domain called PAS
timeless
+
(
tim
+
)
Short-period, long-period,
and arrhythmic flies
Affects locomotion,
eclosion, sleep
Negative element;
tim
+
mRNA levels rise late in the day
TIM protein destabilized by light
TIM proteins feed back negatively on their own
transcription, interacts with PER
Clock
+
(
Clk
+
)
Arrhythmic
Affects locomotion,
eclosion, rhythm
CLK, in combination with CYC, activates transcription of
per
+
and
tim
+
CLK negatively regulates itself
Mutants blind for “lights-on” response
cycle
+
(
cyc
+
)
Arrhythmic
Affects locomotion and
eclosion
CYC, in combination with CLK, activates transcriptions of
per
+
and
tim
+
CYC negatively regulates itself
Mutants respond poorly to light-dark cycles
cryptochrome
+
(
cry
+
)
Photoreceptor
Resets rhythms
Sequence homologous to a photolyase; binds TIM in a
light-dependent manner
Altered light response in mutants
doubletime
+
(
d
+
)
Lengthens cycle in
constant darkness
Affects locomotion, sleep
Casein kinase I involved in phosphorylating PER,
rendering it unstable in absence of TIM
(Adapted from
Emery et al. 2000, Sancar 2000, Harmer et al. 2001, Merrow and Roenneberg 2001, Sokolowski 2001,
Williams and Sehgal 2001
.)
