Helmsman is expressed in both trachea and photoreceptor development: partial inactivation alters tracheal morphology...

We have identified helmsman (hlm), which is expressed in the fruit fly photoreceptor cells during neural network development. Hlm is also expressed in the elongating cells of the embryonic trachea. Both photoreceptor neurons and embryonic trachea cells elongate in precise, targeted growth for cell-to-cell specific recognition. Expression of antisense hlm-interfering RNA during embryogenesis arrests elongation of the developing tracheal cells and blocks maturation. Expression of hlm-interfering RNA during visual system formation results in reduced visual acuity and poor performance in optomotor response, indicative of abnormal neural network development. Hlm is a unique cell surface protein with complement-like protein interaction motifs. We have also cloned hlm from Lucilia cuprina (Australian blowfly), which is approximately 100 million years divergent from Drosophila, and find a remarkable 90% protein identity over the entire 558 amino acid protein. Analysis of the hlm sequence found in other species indicates a significant evolutionary pressure to maintain the hlm protein sequence. Our interpretation is that hlm is involved in cell maturation in both the elongating trachea and elongating photoreceptor cells. Cell adhesion and cell signaling, which are known to use immunoglobulin-like cell adhesion molecules, may use molecular systems analogous to complement to create protein complexes to regulate growth.