Biology Reference
In-Depth Information
11. OTHER TRANSCRIPTION FACTORS WITH KNOWN
EXPRESSION IN THE PROTHORACIC GLAND
In this last section, we will briefly review other transcription factors
that have been directly or indirectly linked to the ecdysone synthesis path-
way (
Table 2.1
). Below, we will highlight seven of them and discuss their
putative functions in the
Drosophila
prothoracic gland.
11.1. WOC (without children)
The
Drosophila woc
gene encodes a transcription factor that harbors eight
C
2
C
2
zinc finger repeats. The
woc
gene is expressed in many tissues, includ-
ing the ring gland, imaginal disks, the brain-ganglion complex, and others.
Homozygous
woc
mutants have overgrown ring glands and fail to pupariate;
however, feeding 20E allows mutants to undergo metamorphosis (
Klose,
Gateff, Emmerich, & Beikirch, 1980; Wismar et al., 2000
), suggesting
WOC plays a role in regulating ecdysone synthesis. This was supported
by the finding that ring glands of
woc
mutants are not able to convert radi-
olabelled cholesterol into 7-dehydrocholesterol. Further, feeding mutants
with 7-dehydrocholesterol, but not cholesterol, leads to a significant increase
in the ecdysone titers (
Warren, Wismar, Subrahmanyam, & Gilbert, 2001
).
Together, these studies indicate that WOC regulates the first step of ecdy-
sone biosynthesis in
Drosophila
, likely through regulating the activity of
7,8-cholesterol dehydrogenase (now known to be Neverland); however,
the mechanism by which WOC achieves this remains unaddressed.
11.2. MLD (molting defective)
The
Drosophila mld
gene encodes a nuclear protein that is predicted to have
seven C
2
H
2
zinc fingers in two clusters in the C-terminal region. Immu-
nodetection showed that MLD protein is present in larval tissues including
the ring gland, salivary gland, fat body, and imaginal disks. Mutations of
mld
result in an arrest of development in the first larval instar. This defect can be
rescued by administration of excess E or 20E, suggesting that
mld
participates
in modulating ecdysone synthesis (
Neubueser et al., 2005
). Semiquantitative
PCR showed that homozygous
mld
mutant first instar larvae have decreased
transcript levels of the ecdysone biosynthetic gene
spookier
, while other
known enzymatic genes remain unaffected or upregulated, suggesting that
spookier
is a target of
mld
in the steroidogenic pathway (
Ono et al., 2006
).
However, restoration of
spookier
expression in the
mld
mutant ring gland
