Distinct Phospholipase C--Dependent Signaling Pathways in the Drosophila Eye and Wing Are Revealed by a New small wing Allele

Corresponding author: Justin R. Thackeray, Clark University, 950 Main St., Worcester, MA 01610., jthackeray{at}clarku.edu (E-mail)

Communicating editor: T. SCHÜPBACH

The Drosophila genome contains a single phospholipase C- (PLC-) homolog, encoded by small wing (sl), that acts as an inhibitor of receptor tyrosine kinase (RTK) signaling during photoreceptor R7 development. Although the existing sl alleles behave genetically as nulls, they may still produce truncated Sl products that could in theory still provide limited PLC- function. Both to identify a true null allele and to probe structure-function relationships in Sl, we carried out an F₁ screen for new sl mutations and identified seven new alleles. Flies homozygous for any of these alleles are viable, with the same short-wing phenotype described previously; however, two of the alleles differ from any of those previously isolated in the severity of the eye phenotype: sl⁹ homozygotes have a slightly more extreme extra-R7 phenotype, whereas sl⁷ homozygotes have an almost wild-type eye. We determined the mutant defect in all seven alleles, revealing that sl⁹ is a molecular null due to a very early stop codon, while sl⁷ has a missense mutation in the highly conserved Y catalytic domain. Together with in vitro mutagenesis of the residue affected by the sl⁷ mutation, these results confirm the role of Sl in RTK signaling and provide evidence for two genetically separable PLC--dependent pathways affecting the development of the eye and the wing.

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