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

Authors: CHRISTIE, ANDREW - University Of Hawaii; Hull, Joe; DICKINSON, PATSY - Bowdoin College

Submitted to: Invertebrate Neuroscience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2020
Publication Date: 3/2/2020
Citation: Christie, A.E., Hull, J.J., Dickinson, P.S. 2020. 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. Invertebrate Neuroscience. 20(5). https://doi.org/10.1007/s10158-020-0238-6.
DOI: https://doi.org/10.1007/s10158-020-0238-6

Interpretive Summary: In decapods such as the American lobster, the cardiac ganglion, which consists of nine neurons, controls cardiac muscle contractions and represents one of the simplest rhythmically active neural networks known. The rhythmic control of this tissue is generated by a combination of electrical and chemical actions. Coordination of this rhythmicity among neurons typically proceeds via the physical channels/junctions between adjacent cells. The types and numbers of genes that contribute to the formation of these channels determine the degree of interaction between the cells and thus mediate the cell-to-cell coordination that manifests in rhythmicity. Transcriptomic datasets facilitate the identification of previously uncharacterized gene products and provide insights into their potential biological function. Thus, a cardiac ganglion specific transcriptome was used to identify genes potentially involved in coordinating the electrical activity among the nine cardiac ganglion neurons. The search identified a larger than expected complement of genes called innexins that are responsible for forming the channels/junctions between cells. This increase in innexin diversity is expected to impact the properties of the channels and thus influence how neuronal rhythmicity is generated and maintained. These findings will be used to guide future studies to examine the biochemical and physiological asepcts of cardiac ganglion function.

Technical 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.