Calx, A Sodium-Calcium Exchanger of Drosophila melanogaster

Author: Schwarz, Erich Marquard

Year: 1996

Degree: Dissertation (Ph.D.)

Advisor: Benzer, Seymour

Committee Members: Benzer, Seymour; Anderson, David J.; Meyerowitz, Elliot M.; Simon, Melvin I.; Sternberg, Paul W.

Option: Molecular Biology; Biochemistry

DOI: 10.7907/M2PR-WT51

Abstract

Calcium extrusion is necessary for cellular survival and suspected to modulate cellular activity. Drosophila phototransduction is a promising system in which to study calcium export, since it is dominated by calcium activity yet, unlike most calcium-dependent signalling pathways, genetically pliable. The multiple roles of calcium flux in Drosophila phototransduction are reviewed in Chapter One.

Calx, a Drosophila ortholog of mammalian 3Na+/1Ca2+ exchangers, was isolated and characterized (Chapter Two). Calx's gene product has ~50% identity to its direct mammalian homologs, with more distant similarities to an exchanger-related superfamily. There exist at least seven alternately spliced adult Calx transcripts, with an alternatively spliced miniexon in Calx's protein-coding region. A full-length Calx cDNA of 5408 bp has lengthy, elaborate 5' and 3' UTRs. Calx transcripts are ubiquitously expressed in embryos and adult heads, with one 5.7 kb transcript expressed in photoreceptors; Calx protein is also ubiquitous in adult heads, with a notable presence in photoreceptors and neuropil. Heterologous expression of Calx in Xenopus oocytes shows that it encodes a bona fide sodium-calcium exchanger; unlike mammalian retinal exchangers, it does not depend on potassium for activity. Calx encodes two novel protein motifs, Calx-α and Calx-β. Both are intragenically duplicated, but they probably have different functions: Calx-α is likely to encode residues central to calcium export, while Calx-β may mediate intracellular signalling or cytoskeletal anchoring.

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