DIVERSE EXPRESSION AND DISTRIBUTION OF SHAKER POTASSIUM CHANNELS DURING THE DEVELOPMENT OF THE DROSOPHILA NERVOUS-SYSTEM

The spatio-temporal expression of Shaker (Sh) potassium channels (Kch) in the developing and adult nervous system of Drosophila has been stu died at the molecular and histological level using specific antisera. Sh Kch are distributed in most regions of the nervous system, but thei r expression is restricted to only certain populations of cells. Sh Kc h have been found in the following three locations: in synaptic areas of neuropile, in axonal fiber tracks, and in a small number of neurona l cell bodies. This wide subcellular localization, together with a div erse distribution, implicates Sh itch in multiple neuronal functions. Experiments performed with Sh mutants that specifically eliminate a fe w of the Sh Kch splice variants clearly demonstrate an abundant differ ential expression and usage of the wide repertoire of Sh isoforms, but they do not support the idea of extensive segregation of these isofor ms among different populations of neurons. Sh Kch are predominantly ex pressed at late stages of postembryonic development and adulthood. Str ikingly, wide changes in the repertoire of Sh splice isoforms occur so me time after the architecture of the nervous system is complete, indi cating that the expression of Sh Kch contributes to the final refineme nts of neuronal differentiation. These late changes in the expression and distribution of Sh Kch seem to correlate with activity patterns su ggesting that Sh Kch may be involved in adaptative mechanisms oi excit ability.