POLLUX, A NOVEL DROSOPHILA ADHESION MOLECULE, BELONGS TO A FAMILY OF PROTEINS EXPRESSED IN PLANTS, YEAST, NEMATODES, AND MAN

Adhesion molecules have pivotal roles in cellular processes critical t o the development and maintenance of multicellular organisms. Here we describe a new member of the adhesive repertoire encoded by the Drosop hila pollux (pix) gene. Marked by a novel 74-amino-acid domain, Pix be longs to a highly conserved family with members in plants, yeast, nema todes, and man, including the human oncoprotein TRE17. Essential for v iability, pix mutant analysis indicates that larval death is attributa ble to asphyxiation brought on by fluid-congested tracheal tubes. Ultr astructural examination of mutant tracheae reveals defects in cell-ext racellular matrix contacts. During embryogenesis, Pix uniformly covers the apical surface of cellular blastoderm cells. It is later found re gionally concentrated along subsets of central nervous system axon pat hways and on the apical surface of the trachea's tubular epithelium. C ell attachment assays demonstrate that pix can serve as a ligand for c ell surface integrins. Pix also contains a motor neuron-selective adhe sive site, multiple proteoglycan-binding motifs, and a leucine zipper: all suggest possible associations with additional components of the a dhesion complex.