In flies, escape behaviour is mediated by the neurons of the Giant-Fibre System, in which
the Giant Fibre (GF) forms an electrical synapse with the Tergotrochanteral Motoneuron
(TTMn). In flies carrying the shaking B2 mutation, dye coupling is disrupted between the GF
and TTMn, indicating that the shaking B gene is required for electrical-synapse formation in
the GF system. Expression of Shaking B in Xenopus oocyte pairs shows that Shaking B
proteins are functional components of gap junctions. We have called this family of gapjunction
proteins the innexins. The shaking B locus encodes three members of the innexin
family: Shaking B (neural), Shaking B (n+16) and Shaking B (lethal). Targeted expression
show that Shaking B (n+16) expression presynaptically in the GF and Shaking B (lethal)
postsynaptically in the TTMn is required for electrical synapse formation between these
neurons. In vitro expression of ShakB (n+16) and ShakB (lethal) in neighbouring Xenopus
oocytes results in the formation of heterotypic intercellular channels which are
asymmetrically gated by transjunctional voltage and exhibit classical rectification. These data
show that rectification is achieved by differential regulation of the pre- and post-synaptic
elements of structurally asymmetric junctions. In vertebrates, gap-junction channels were
thought to be entirely composed of a different protein family, called connexins, but recent
work (not at Sussex) has shown that functional innexin-like proteins, termed pannexins, are
also expressed in vertebrates. The simple diploblastic organism Hydra appears to possess
only innexins - so we conclude that innexins are the primordial gap-junction molecules, while
connexins evolved more recently in the deuterostomes.
Biography
Jonathan Bacon is Professor of Neuroscience in the School of Life Sciences, University of
Sussex, UK, and is Adjunct Professor of Neuroscience in the Department of Neuroscience,
University of Arizona, Tucson. His first degree was at Cambridge. After a year teaching in
Jamaica, he took an MSc and a PhD at Manchester, and postdocs in: Seewiesen, Germany;
Albany, USA; Basel, Switzerland. He joined the faculty in Biology at the University of Sussex
in 1984, where he was awarded the 1987 President’s Medal of the Society for Experimental
Biology, and was the Dean of Life Sciences from 2002-2009. His research examines: insect
behaviour and its underlying neural circuitry; gap-junctional (innexin-mediated) cell-cell
communication; foraging behaviour of Pharaoh's ants and honey bees.