Irregular chiasm-C-roughest, a member of the immunoglobulin superfamily, affects sense organ spacing on the Drosophila antenna by influencing the positioning of founder cells on the disc ectoderm

We describe a role for Irregular chiasmC-roughest (IrreC-rst), an immunoglo bulin (Ig) superfamily member, in patterning sense organs on the Drosophila antenna. IrreC-rst protein is initially expressed homogeneously on apical profiles of ectodermal cells in regions of the antennal disc. During specif ication of founder cells (FCs), the intracellular protein distribution chan ges and becomes concentrated in regions where specific intercellular contac ts presumably occur. Loss of function mutations as well as misexpression of irreC-rst results in an altered arrangement of FCs within the disc compare d to wildtype. Sense organ development occurs normally, although spacing is affected. Unlike its role in interommatidial spacing, irreC-rst does not a ffect apoptosis during antennal development. We propose that IrreC-rst affe cts the spatial relationship between sensory and ectodermal cells during FC delamination.