R132 Dispatch
Drosophila development: A receptor for ommatidial recruitment
Christian Klämbt
Recent work shows that the differentiation of all the
cell types found in the compound eye of Drosophila
melanogaster is induced by reiterative activation of the
EGF receptor.
Address: Institut für Entwicklungsbiologie, Universität zu Köln, 50923
Köln, Germany.
Electronic identifier: 0960-9822-007-R0132
Current Biology 1997, 7:R132–R135
© Current Biology Ltd ISSN 0960-9822
In recent years, studies on eye development in the fruitfly
Drosophila have greatly contributed to our understanding of
many biological issues, from the roles cell–cell interactions
play in pattern formation to the nature of components that
make up the intracellular signalling pathways downstream
of receptor tyrosine kinases. As a result of many studies,
the mechanisms that control the generation of a single
photoreceptor (R7) have been largely unravelled, whereas
the processes that generate the other cell types found in
the eye have remained elusive. Now data have been
obtained that support a simple model explaining the
recruitment of all cell types found in the eye [1].
The Drosophila compound eye comprises about 750–800
single units, the facets or ommatidia, each containing 20
cells. Each ommatidium has six outer and two inner
photoreceptors — R1–R6 and R7 and R8, respectively —
which collect the visual input and transmit it to the optic
lobes. Four cone cells secrete the lens, and two primary
and six secondary and tertiary pigment cells optically insu-
late the individual ommatidia. Eye development starts
during larval stages from an epithelial monolayer, the eye
imaginal disc (Fig. 1). Up to the third larval stage, all eye
imaginal disc cells divide. From then on, cell divisions
occur in two waves, which sweep anteriorly across the eye
disc. In between these zones of proliferation, a small
groove known as the morphogenetic furrow sweeps anteri-
orly across the disc. Ommatidial development is initiated
Figure 1
The Drosophila eye (a) comprises 750–800
single ommatidia (b), each of which contains
20 cells. (c) The different cells, illustrated in
these cross-sections at three different levels
of an ommatidium, can be easily recognized
by morphological and physiological criteria.
(d) During larval stages, eye development is
initiated in the eye imaginal disc. The
morphogenetic furrow sweeps anteriorly
across the disc, leaving more and more
mature ommatidia behind. (e) The different
stages of ommatidial development are
depicted. Immediately posterior to the
morphogenetic furrow, arc-like structures
appear. At the top of each arc, the R8 cell is
specified; subsequently, photoreceptor cells
R2 and R5, and then R3 and R4 are added to
form the five-cell precluster. The other
ommatidial cells are recruited from the cells
generated in the second mitotic wave, again
in a sequential manner: first R1 and R6, then
R7 followed by the four cone cells. (f) During
pupal stages, the different pigment cells are
added.
8
2
5
3
4
1
6
7
8
2
5
3
4
1
6
7
8
2
5
3
4
1
6
7
8
2
5
8
2
5
1
6
3
4
7
8
2
5
3
4
8
8
R7
R4
R5
R8
R6
R1
R2
R3
Cone cell
1° pigment cell
2° pigment cell
Bristle
3° pigment cell
Morphogenetic furrow
Pupal stage
(a) (b) (c)
(d) (e) (f)
Anterior
© 1997 Current Biology