ESSENTIAL AND NEURAL TRANSCRIPTS FROM THE DROSOPHILA SHAKING-B LOCUS ARE DIFFERENTIALLY EXPRESSED IN THE EMBRYONIC MESODERM AND PUPAL NERVOUS-SYSTEM

The shaking-B gene of Drosophila encodes two functions: one specifical ly neural and the other required for viability. Flies carrying neural mutations show a range of defects, the best characterized of which is a disruption of some synapses in the giant fibre system, while mutatio ns in the essential function cause animals to die as first instar larv ae. We have characterised an essential transcript from this locus and show that mutant lesions underlying two lethal shaking-B alleles map t o its coding sequence. We also propose a new model for the topologies of Shaking-B proteins and their relatives. Essential shaking-B transcr ipts are found in embryonic mesodermal derivatives, while during metam orphosis both essential and neural transcripts are dynamically express ed in the pupal nervous system. Although the expression patterns of th ese transcripts overlap in many cells, only the neural form is express ed in the giant fibre cell bodies and the lamina and medulla of the op tic Iobes. This observation correlates with the phenotypes of mutation s which disrupt the coding region of this neural transcript. On the ba sis of the expression patterns of shaking-B transcripts and the phenot ypes conferred by mutations of shaking-B and homologous genes, we sugg est that Shaking-B proteins and their homologues may be involved in th e organisation of cellular membranes. (C) 1993 Academic Press, Inc.