The evolution of innexins and their function in the electrical synapses of invertebrates
The innexins are a recently characterized protein family that comprises gap
junctions in a number of invertebrate taxa. In this thesis, novel innexins from the snail
Lymnaea stagnalis, the cockroach Periplaneta Americana and the lobster Homarus
gammarus are described. These results extend our knowledge of this gene family in
invertebrates. Also, novel innexin-like and connexin genes are identified in the
ascidian Ciona intestinalis. These results help to formulate a hypothesis about the
evolutionary origins of gap-junctional proteins.
The role of innexins as gap-junction forming molecules is investigated in the
lobster stomatogastric nervous system (STG). In situ hybridizations reveal the
patterns of expression of these novel innexins, while an RNAi study attempted, but
failed, to investigate the relationship between developmental changes in innexinmediated
electrical coupling and the maturation of motor networks in the STG.
Finally, using an antibody against the fly innexin Shaking-B, I investigate the
evolution of the Giant Fiber System (GFS). The GFS in dipterous insects mediates
the escape response. The identified neurons of the system are connected with
electrical synapses formed by innexin proteins. The Shaking-B protein localizes at
these synapses. A comparative study of a number of fly species showed
conservation of some GFS synapses but species specific differences in others.
These results inform our thinking about the evolution of the GFS and its underlying