Biology Reference
In-Depth Information
A
20E
Ecdysone receptor
Active ecdysone receptor
Early puff
genes
Late puff
genes
B
Pupariation
Head eversion
Prepupa
Third instar
t
20E peaks
EcR-A EcR-B1
EcR-A
BR-C
E75A
NO
E75B
DHR4
DHR3
Early genes
Early-late genes
b
ftz-f1
Mid-prepupal gene
Late genes
NO
Nitric oxide
Figure 2.1 Ecdysone hierarchy. (A) Ashburner model. The hormone-bound and thus
active ecdysone receptor directly induces the expression of early puff genes and re-
presses late puff genes. A small set of early puff genes repress their own expression
and are required for the induction of a large set of late puff genes. (B) Overview of Dro-
sophila ecdysone hierarchy genes at the onset of metamorphosis. The expression of
genes is shown in bars with different shades of gray representing different gene cate-
gories (see inset), and the length of the bars indicates the approximate duration of their
expression. Positive and inhibitory interactions are shown. Ecdysone peaks are shown in
dotted boxes at the top, and approximate timing of puparium formation and head ever-
sion are indicated by dotted lines.
