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Mol. Cell. Biol., Mar 1996, 1179-1188, Vol 16, No. 3
EC Lee, X Hu, SY Yu and NE Baker
R8 photoreceptor cells play a primary role in the differentiation of
Drosophila eyes. In scabrous (sca) mutants, the pattern of R8 photoreceptor
differentiation is altered. The sca gene is predicted to encode a secreted
protein related in part to fibrinogen and tenascins. Using expression in
Drosophila Schneider cells, we showed that sca encoded a dimeric
glycoprotein which was secreted and found in soluble form in the tissue
culture medium. The sca protein contained both N- and O-linked
carbohydrates and interacted with heparin. This Schneider cell protein was
similar to protein detected in embryos. We showed that sca mutations, along
with conditional alleles of Notch (N) and Delta (Dl), each affected the
pattern of cells expressing atonal (ato), the proneural gene required for
R8 differentiation. In normal development, about 1 cell in 20
differentiates into an R8 cell; in the others, ato is repressed. N and Dl
were required to repress ato in the vicinity of R8 cells, whereas sca had
effects over several cell diameters. Certain antibodies detected uptake of
sca protein several cells away from its source. The overall growth
factor-like structure of sca protein, its solubility, and its range of
effects in vivo are consistent with a diffusible role that complements
mechanisms involving direct cell contact. We propose that as the
morphogenic furrow advances, cell secreting sca protein control the pattern
of the next ommatidial column.
Copyright © 1996, American Society for Microbiology
The scabrous gene encodes a secreted glycoprotein dimer and regulates proneural development in Drosophila eyes
Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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