doi: 10.1242/10.1242/dev.00534
Mechanism of hedgehog signaling during Drosophila eye development
Kartik S. Pappu1,
Rui Chen2,
Brooke W. Middlebrooks3,
Catherine Woo4,
Ulrike Heberlein5 and
Graeme Mardon1,2,3,6,7,*
1 Program in Developmental Biology, Baylor College of Medicine, One Baylor
Plaza, Houston, TX 77030, USA
2 Department of Molecular and Human Genetics, Baylor College of Medicine, One
Baylor Plaza, Houston, TX 77030, USA
3 Department of Pathology, Baylor College of Medicine, One Baylor Plaza,
Houston, TX 77030, USA
4 Biomedical Initiatives, University-wide AIDS Research Program, University of
California Office of the President, 300 Lakeside Drive, 6th Floor, Oakland, CA
94612, USA
5 Department of Anatomy, University of California San Francisco, Box 0452, 513
Parnassus, San Francisco, CA 94143-0452, USA
6 Department of Ophthalmology, Baylor College of Medicine, One Baylor Plaza,
Houston, TX 77030, USA
7 Department of Neuroscience, Baylor College of Medicine, One Baylor Plaza,
Houston, TX 77030, USA
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Fig. 1. hh functions synergistically with ey to induce Eya
expression and photoreceptor differentiation. (A-F) All panels show wing discs
(anterior towards the left and dorsal upwards) with different combinations of
UAStransgenes driven by the 30A-GAL4 driver. The expansion of the
wing disc in all panels is a result of overexpression of either dpp
or hh, and reflects the capacity of these genes to induce growth and
proliferation of imaginal disc cells. (A,D) ey and dpp
co-expression in a ring around the wing pouch induces Eya expression (A) and
photoreceptor differentiation, but only in the posterior compartment.
Endogenous Eya expression in the wing disc appears as vertical stripes of
staining in the anterior and posterior compartment (arrowheads in A). (B,E)
When ey and hh are co-expressed, Eya is expressed (B) and
photoreceptors differentiate, but only in the anterior compartment. (C,F)
Overexpression of ey, dpp and hh together induces Eya
expression (C) and photoreceptors in both compartments of the disc pouch.
(D-F) Photoreceptor differentiation is visualized by an antibody to the
pan-neuronal protein Elav.
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Fig. 2. eya and dpp can bypass the requirement for hh to
induce ectopic photoreceptor differentiation in the wing disc. (A-I) All
panels show late third instar wing discs (anterior towards the left and dorsal
upwards) with different combinations of UAS-transgenes driven by the
30A-GAL4 driver. (A,C,D,F) Misexpression of ey, dpp and
eya (A,D), but not ey, hh, eya and so (C,F), in the
wing disc induces Dac expression (A,C) and photoreceptor differentiation in
the anterior and posterior compartments. (B,E) This effect is more penetrant
when ey, dpp, eya and so are misexpressed. (G-I)
Misexpression of ey, dpp, eya and so together in the wing
disc in the presence of a lacZ enhancer trap in the hh locus
(hhP30). The same wing disc stained with anti-Dac (red,
G), anti-ß-galactosidase (green, H) or a merge of the two channels (I)
are shown. Dac expression is induced in a ring around the wing pouch (D) but
hh expression (H) is restricted to the posterior compartment. (D-F)
Photoreceptor differentiation is visualized by an antibody to the pan-neuronal
protein Elav.
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Fig. 3. ci mutant clones in the eye disc do not block Eya expression, MF
initiation, progression or photoreceptor differentiation. (A,B) Each set of
four panels in A and B show the same eye disc containing ci mutant
clones stained with (A) anti-ß-galactosidase, anti-Ci, anti-Senseless and
a merge of all three channels or (B) anti-ß-galactosidase, anti-Ci,
anti-Eya and a merge. The yellow arrows in A and B mark clonal areas. No
obvious disruption in Eya or Senseless staining (A) is observed in
ci-null mutant clones. (C) Thin plastic sections of adult eyes
containing ci mutant tissue. Mutant clones are negatively marked by
the lack of pigment granules. Photoreceptor differentiation is normal even in
very large clones of ci mutant tissue. (D,F) Animals heterozygous for
ci94 or homozygous for ci94, but
rescued by one copy of the P[ci+] transgene, have normal Ci
staining in the wings disc (D) and adult wings (F). (E,G) By contrast,
induction of mutant clones in the anterior compartment of the wing disc leads
to loss of Ci in the wing disc (arrow, E) and disruption of pattern in the
anterior adult wing disc (arrow in G).
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Fig. 4. Posterior margin smo mutant clones block Eya expression and
photoreceptor differentiation. (A-G) The same eye disc stained with
anti-ß-galactosidase (red in A,D,E,G), anti-Eya (cyan in B,D), anti-Elav
(green in F,G) and anti-Senseless, an R8 photoreceptor-specific marker (green
in C,D). The clone boundaries are marked with broken white lines (A,D,E,G).
(C,D,F,G) smo clones are negatively marked by the absence of
ß-galactosidase and lack expression Senseless (C,D) or the pan-neuronal
marker Elav (F,G). (B,D) Loss of Eya expression in posterior margin clones (B;
yellow arrow in D) and a reduction of Eya expression internally in large
smo clones (white arrow in D). (D,G) Furrow progression is delayed in
internal smo clones, but up to two rows of photoreceptor clusters
differentiate in mutant tissue (yellow arrowheads in D,G).
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Fig. 5. Co-expression of dpp and eya rescues photoreceptor
differentiation and furrow progression in smo mutant clones. (A-H)
Each set of three panels in A-H depicts the same disc containing large
smo clones stained for anti ß-galactosidase (red), Anti-Elav
(green) or a merge of the two. The ey-GAL4 driver was used to induce
transgene expression in all cases. (A-D) Neither dpp (A,C) nor
eya (B,D) expression alone can rescue the loss of photoreceptor
differentiation in posterior margin smo clones (A,C) or the slowing
of furrow progression in internal smo clones (arrows in B,D). (E,F)
Posterior margin smo clones expressing both dpp and
eya differentiate photoreceptors as visualized by Elav
immunoreactivity (arrow in E). Furrow progression is not delayed in internal
smo clones expressing dpp and eya (arrow in F).
(G,H) Similarly, co-expression of dpp, eya and so also
rescues photoreceptor differentiation and furrow progression in smo
clones, often inducing ectopic furrows from anterior smo clonal areas
(arrows in G,H).
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Fig. 6. A model for the genetic network that controls retinal determination in
Drosophila. hh is required for both dpp and eya
expression during photoreceptor differentiation (see text for additional
details).
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© The Company of Biologists Ltd 2003
