Mutations in shaking-B prevent electrical synapse formation in the Drosophila giant fiber system

Abstract

The giant fiber system (GFS) is a simple network of neurons that mediates visually elicited escape behavior in Drosophila. The giant fiber (GF), the major component of the system, is a large, descending interneuron that relays visual stimuli to the motoneurons that innervate the tergotrochanteral jump muscle (TTM) and dorsal longitudinal flight muscles (DLMs). Mutations in the neural transcript from the shaking-B locus abolish the behavioral response by disrupting transmission at some electrical synapses in the GFS. This study focuses on the role of the gene in the development of the synaptic connections. Using an enhancer-trap line that expresses lacZ in the GFs, we show that the neurons develop during the first 30 hr of metamorphosis. Within the next 15 hr, they begin to form electrical synapses, as indicated by the transfer of intracellularly injected Lucifer yellow. The GFs dye-couple to the TTM motoneuron between 30 and 45 hr of metamorphosis, to the peripherally synapsing interneuron that drives the DLM motoneurons at approximately 48 hr, and to giant commissural interneurons in the brain at approximately 55 hr. Immunocytochemistry with shaking-B peptide antisera demonstrates that the expression of shaking-B protein in the region of GFS synapses coincides temporally with the onset of synaptogenesis; expression persists thereafter. The mutation shak-B2, which eliminates protein expression, prevents the establishment of dye coupling shaking-B, therefore, is essential for the assembly and/or maintenance of functional gap junctions at electrical synapses in the GFS.

Morphological characterization of the antennal lobes in the Mediterranean fruit fly Ceratitis capitata

“…8), as shown with unilateral antennal backfill using TMR-DA, which resulted in a lower level of contralateral staining with respect to NB. The contralateral staining observed in the case of NB could be due to the presence of gap junctions that might couple projections of ORNs among different glomeruli: in fact, gap junctions are permeable to the small NB molecules (MW 287) (Phelan et al 1996;Haag and Borst 2005;Anava et al 2009), but not to the ten times larger TMR-DA molecules (MW 3000). This hypothesis seems to be confirmed by the fact that, after staining the contralateral AL, the NB tracer proceeds to be incorporated also in the contralateral antennal nerve, which is not the case of unilateral TMR-DA backfills.…”

DE-Cadherin, a Core Component of the Adherens Junction Complex Modifies Subcellular Localization of theDrosophilaGap Junction Protein Innexin2

“…Genome sequencing projects identified eight innexin genes in the fruit fly Drosophila, however, only a few mutants exist that have been molecularly and functionally characterized. It has been shown that innexin1 (ogre) and innexin8 (shakingB) are involved in the physiology of the giant fibre and the adult visual systems (Watanabe and Kankel 1990;Curtin et al 2002;Krishnan et al 1993;Phelan et al 1996Phelan et al , 2005Shimohigashi and Meinertzhagen 1998;Zhang et al 1999;Jacobs et al 2000); innexin4 (zero population growth) controls germ cell differentiation (Tazuke et al 2002;Gilboa et al 2003) and we have recently shown that during foregut morphogenesis, innexin2 is a Wingless/WNT target gene that coordinates epithelial morphogenesis . Mutants for innexin2 (kropf), which lack both their maternal and zygotic innexin2 contributions fail to develop any epithelial tissues, and overexpression of innexin2 in the epidermis results in multilayering and irregular cell shapes suggesting that innexin2 is a key factor to control epithelial organization during morphogenesis of tissues and organs in the body (Bauer et al 2004).…”

Immunocytochemical study of gap junction-related protein, innexin 2, in Periplaneta americana (Blattodea: Blattidae)

“…Electrical synapse defects occur in shak-B mutants in the interneurons connected to the optic nerve and giant nerve systems; thus, shak-B was predicted as the gene of gap junction proteins in fruit flies (Phelan et al, 1996). A similar protein family found in fruit flies and nematodes was named innexin (INvertebrate conEXIN) (Phelan et al, 1998a).…”