Connexin 35b expression in the spinal cord of Danio rerio embryos and larvae.

Electrical synapses are expressed prominently in the developing and mature nervous systems. Unlike chemical synapses, little is known about the developmental role of electrical synapses, reflecting the limitations imposed by the lack of selective pharmacological blockers. At a molecular level, the building blocks of electrical synapses are connexin proteins. In this study, we report the expression pattern for neuronally expressed connexin 35b (cx35b), the zebrafish orthologue of mammalian connexin (Cx) 36. We find that cx35b is expressed at the time of neural induction, indicating a possible early role in neural progenitor cells. Additionally, cx35b localizes to the ventral spinal cord during embryonic and early larval stages. We detect cx35b mRNA in secondary motor neurons (SMNs) and interneurons. We identified the premotor circumferential descending (CiD) interneuron as one interneuron subtype expressing cx35b. In addition, cx35b is present in other ventral interneurons of unknown subtype(s). This early expression of cx35b in SMNs and CiDs suggests a possible role in motor network function during embryonic and larval stages.