MIDLINE FASCICLIN - A DROSOPHILA FASCICLIN-I-RELATED MEMBRANE-PROTEINLOCALIZED TO THE CNS MIDLINE CELLS AND TRACHEA

Drosophila Fasciclin I is the prototype of a family of vertebrate and invertebrate proteins that mediate cell adhesion and signaling. The mi dline fasciclin gene encodes a second Drosophila member of the Fascicl in I family. Midline Fasciclin largely consists of four 150 amino acid repeats characteristic of the Fasciclin I family of proteins. Immunos taining and biochemical analysis using Midline Fasciclin antibodies in dicates that it is a membrane-associated protein, although the sequenc e does not reveal a transmembrane domain. The gene is expressed in a d ynamic fashion during embryogenesis in the blastoderm, central nervous system midline cells, and trachea, suggesting it plays multiple devel opmental roles. Protein localization studies indicate that Midline Fas ciclin is found within cell bodies of midline neurons and glia, and on midline axons. Initial cellular analysis of a midline fasciclin loss- of-function mutation reveals only weak defects in axonogenesis. Howeve r, embryos mutant for both midline fasciclin and the abelson nonrecept or tyrosine kinase, show more severe defects in axonogenesis that rese mble fasciclin I abelson double mutant phenotypes. (C) 1998 John Wiley & Sons, Inc.