GENETIC-ANALYSIS OF LAMININ-A IN DROSOPHILA - EXTRACELLULAR-MATRIX CONTAINING LAMININ-A IS REQUIRED FOR OCELLAR AXON PATHFINDING

Genetic analysis of the Laminin A (LamA) gene in Drosophila reveals th at distinct classes of sensory axons have different requirements for e xtracellular matrix (ECM) containing laminin A versus epithelial cell surfaces, In the eye-antenna imaginal disc, the nerve from the three s imple eyes (ocelli) to the brain is pioneered by a population of trans ient ocellar neurons whose axons extend on an ECM that covers and conn ects the disc epithelium and brain. Axons from neighboring mechanosens ory (bristle) neurons extend under the ECM in direct contact with the surface of the disc cells, and pioneer a different axon pathway that e nters the brain in a different location, In LamA mutants, the ocellar pioneer axons display striking pathfinding defects, while neighboring bristle axons appear normal; the ocellar pioneers usually extend in th e proper direction, adhering to the epithelium and sometimes fascicula ting with mechanosensory axons, but they invariably fail to reach the brain.