Echinoid synergizes with the Notch signaling pathway in Drosophila mesothorax bristle patterning
2003
echinoid ( ed ) encodes an immunoglobulin domain-containing
cell adhesion molecule that negatively regulates the Egfr signaling pathway
during Drosophila photoreceptor development. We show a novel function
of Ed, i.e. the restriction of the number of notum bristles that arise from a
proneural cluster. Thus, loss-of-function conditions for ed give rise
to the development of extra macrochaetae near the extant ones and increase the
density of microchaetae. Analysis of ed mosaics indicates that extra
sensory organ precursors (SOPs) arise from proneural clusters of
achaete-scute expression in a cell-autonomous way. ed
embryos also exhibit a neurogenic phenotype. These phenotypes suggest a
functional relation between ed and the Notch (N) pathway. Indeed,
loss-of-function of ed reduces the expression of the N pathway
effector E(spl)m8 in proneural clusters. Moreover, combinations of
moderate loss-of-function conditions for ed and for different
components of the N pathway show clear synergistic interactions manifested as
strong neurogenic bristle phenotypes. We conclude that Ed is not essential
for, but it facilitates, N signaling. It is known that the N and Egfr pathways
act antagonistically in bristle development. Consistently, we find that Ed
also antagonizes the bristle-promoting activity of the Egfr pathway, either by
the enhancement of N signalling or, similar to the eye, by a more direct
action on the Egfr pathway.
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