Abstract
Echinoid (Ed) is an immunoglobulin domain-containing cell adhesion molecule (CAM). Ed negatively regulates epidermal growth factor (EGF) receptor signaling pathway during eye development and cooperates with Notch pathway during sensory bristle development. Moreover, Ed is a component of adherens junctions (AJ) that cooperates with DE-cadherin to mediate cell adhesion. To identify novel molecules associated with the intracellular domain of Ed, affinity chromatography of embryonic lysate followed by the protein identification with matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry has been conducted. One major co-precipitated protein was identified to be the Drosophila homologue of serine-threonine kinase receptor-associated protein (D-STRAP). Although Ed associates with D-STRAP, however it was shown that STRAP is involved in the transforming growth factor-β (TGF-ß) signaling in mammalian cell cultures. To determine the function of D-STRAP during development, we generated homozygous D-STRAP mutant clones in eye imaginal discs. We observed apical constriction in D-STRAP clones that in turn causes the ommatidial disorganization and mislocalization of photoreceptor nuclei toward the basally localized optic stalk. However, the specification of mutant photoreceptor neurons is not affected. To determine whether D-STRAP is involved in the TGF-ß pathway, we examined the expression of phosphorylated form of Mothers against decapentapelagic (pMad), a reporter of TGF-ß activation during furrow progression. In contrast to thick veins (tkv) clones, we failed to detect the loss of pMad staining in D-STRAP clones. Together, we conclude that D-STRAP may not involved in the TGF-ß signaling pathway.