Biology Reference
In-Depth Information
Figure 11.3
The exon/intron structure of the
D. melanogaster period
gene. The gene is
≈
7 kb long,
with seven exons. The location of the
per
L
,
per
0
, and
per
S
mutations are indicated, as is the region
which codes for the variable number (17, 20, or 23) of Thry/Gly repeats.
functions common to all (clock-type functions), whereas species-specific dif-
ferences, such as love songs, locomotor activity, and eclosion profiles, may be
encoded within the variable regions (
Kyriacou 1990
).
Clock
+
,
timeless
+
,
cycle
+
, and
doubletime
+
are components of the circadian
clock (
Kyriacou 1993
,
Table 11.2
). In addition, autosomal mutations induce flies
to eclose early in a light-dark cycle; flies with mutations of
phase-angle
+
emerge
in the pre-dawn part of the cycle instead of just after dawn, while flies with
mutations of
gate
+
fail to eclose during this narrow time window.
The
cryptochrome
+
(
cry
+
) gene is an important clock gene because it encodes
a critical circadian photoreceptor in
Drosophila
(
Egan et al. 1999, Emery et al.
2000
). The gene product CRY belongs to a family of blue light-sensitive proteins
that includes photolyases and plant blue-light photoreceptors. Flies overexpress-
ing CRY are hypersensitive to light. The CRY protein is probably the only dedi-
cated circadian photoreceptor in
Drosophila
(
Emery et al. 2000
).
11.5.1.2 Song-Cycle Behavior in Transgenic
Drosophila
The courtship song is produced when
D. melanogaster
males vibrate their
wings. The song consists of two components: 1) courtship hums, and 2) a series
of pulses with interpulse intervals that can fluctuate between 15 and 85 millisec-
onds (ms) (
Kyriacou and Hall 1989
). The variation in interpulse intervals ranges
from a period of 56ms in
D. melanogaster
and 35-40ms in
D. simulans
. The
males of
D. melanogaster
with the
per
S
mutation sing with 40-ms periods,
per
L
males sing with 76-ms periods, and
per
0
males are arrhythmic.
The genetic basis of species-specific song instructions was confirmed by the
transfer of the
per
+
gene cloned from
D. simulans
into
D. melanogaster
via