In silico analyses suggest the cardiac ganglion of the lobster, Homarus americanus, contains a diverse array of putative innexin/innexin-like proteins, including both known and novel members of this protein family.

Abstract

Gap junctions are physical channels that connect adjacent cells, permitting the flow of small molecules/ions between the cytoplasms of the coupled units. Innexin/innexin-like proteins are responsible for the formation of invertebrate gap junctions. Within the nervous system, gap junctions often function as electrical synapses, providing a means for coordinating activity among electrically coupled neurons. While some gap junctions allow the bidirectional flow of small molecules/ions between coupled cells, others permit flow in one direction only or preferentially. The complement of innexins present in a gap junction determines its specific properties. Thus, understanding innexin diversity is key for understanding the full potential of electrical coupling in a species/system. The decapod crustacean cardiac ganglion (CG), which controls cardiac muscle contractions, is a simple pattern-generating neural network with extensive electrical coupling among its circuit elements. In the lobster, Homarus americanus, prior work suggested that the adult neuronal innexin complement consists of six innexins (Homam-Inx1-4 and Homam-Inx6-7). Here, using a H. americanus CG-specific transcriptome, we explored innexin complement in this portion of the lobster nervous system. With the exception of Homam-Inx4, all of the previously described innexins appear to be expressed in the H. americanus CG. In addition, transcripts encoding seven novel putative innexins (Homam-Inx8-14) were identified, four (Homam-Inx8-11) having multiple splice variants, e.g., six for Homam-Inx8. Collectively, these data indicate that the innexin complement of the lobster nervous system in general, and the CG specifically, is likely significantly greater than previously reported, suggesting the possibility of expanded gap junction diversity and function in H. americanus.