Molecular and Biophysiological Differences in Neuronal Innexin Gap Junctions Likely Underlie Unique Circuit Behaviors in Hydra vulgaris

Abstract

Connexins, in vertebrates, and Innexins, in invertebrates, are non-homologous gene families that are both known to form functionally similar channels. Connexins have been well characterized both functionally and molecularly but there is still a large gap of characterization within the innexin gene family. The genome of the freshwater cnidarian Hydra vulgaris contains 15 predicted innexins, of which, 5 are expressed exclusively in the nervous system. It is presumed that these innexins are expressed in the different circuits of the hydra nervous system. There are 3 well described circuits which regulate 3 different behaviors in hydra; The contractile burst (CB) circuit which coordinates contractions, rhythmic potential 1 (RP1) which coordinates elongations, and rhythmic potential 2 (RP2) which coordinates radial contractions/egestion. Here I present data to show that hydra innexins are capable of forming gap junctions. The electrophysiology associated with hydra innexins is similar to that of connexins which undergo voltage dependent inactivation. There is clear delineation of properties between INX2, which is expressed in the CB circuit, and the innexins expressed in other neuronal circuits. The CB circuit is known to undergo regular activations which correlates with the contractile behavior of hydra. By removing the hypostome I reveal the presence of CB pacemakers within the hypostome and present a way to facilitate further investigation into regeneration of CB and RP circuits. Lastly, in collaboration with the Fairhall lab, I present imaging and analysis techniques that facilitate the construction of a biomechanical model to simulate the behaviors of hydra.