Distribution of the gap junction protein connexin 35 in the central nervous system of developing zebrafish larvae

Abstract

Gap junctions are membrane specializations that allow the passage of ions and small molecules from one cell to another. In vertebrates, connexins are the protein subunits that assemble to form gap junctional plaques. Connexin-35 (Cx35) is the fish ortholog of mammalian Cx36, which is enriched in the retina and the brain and has been shown to form neuronal gap junctions. As a first step toward understanding the role of neuronal gap junctions in central nervous system (CNS) development, we describe here the distribution of Cx35 in the CNS during zebrafish development. Cx35 expression is first seen at 1 day post fertilization (dpf) along cell boundaries throughout the nervous system. At 2 dpf, Cx35 immunoreactivity appears in commissures and fiber tracts throughout the CNS and along the edges of the tectal neuropil. In the rhombencephalon, the Mauthner neurons and fiber tracts show strong Cx35 immunoreactivity. As the larva develops, the commissures and fiber tracts continue to be immunoreactive for Cx35. In addition, the area of the tectal neuropil stained increases vastly and tectal commissures are visible. Furthermore, at 4–5 dpf, Cx35 is seen in the habenulae, cerebellum and in radial glia lining the rhombencephalic ventricle. This pattern of Cx35 immunoreactivity is stable at least until 15 dpf. To test whether the Cx35 immunoreactivity seen corresponds to functional gap junctional coupling, we documented the number of dye-coupled neurons in the hindbrain. We found several dye-coupled neurons within the reticulospinal network indicating functional gap junctional connectivity in the developing zebrafish brain.

Beta‐cell excitability and excitability‐driven diabetes in adult Zebrafish islets

“…Connexin 36 is the primary gap junction protein in mammalian islets (Farnsworth and Benninger ). Connexin 35b is the major ortholog of mouse connexin 36 in fish (Jabeen and Thirumalai ; Carlisle and Ribera ; Watanabe ). It has been well‐characterized in zebrafish brain (Jabeen and Thirumalai ; Carlisle and Ribera ), and both cDNA (Fig.…”

Electron Microscopic Reconstruction of Functionally Identified Cells in a Neural Integrator

“…We speculate that these darkenings are some kind of cell junction. Due to limited image resolution, we cannot ascertain whether these are gap junctions, which are known to exist in the developing larval zebrafish hindbrain [37]. …”

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

“…The goal of our study was to identify neurons that express cx35b , so our focus was on the soma, where detection of mRNA and soluble fluorescent reporter proteins is most reliable. In contrast, Jabeen and Thirumbalai () analyzed where the immunoreactivity was present within the central nervous system without identifying the immunoreactive cells. The broad distribution pattern detected using the Cx35 antibody could reflect expression of immunoreactive protein in many neurons or in a subset of neurons that have elaborate processes that extend throughout the examined region.…”

“…Second, because of a genome-wide duplication event during the teleost divergence, many zebrafish genes appear in duplicate compared with mammalian genomes (Holland and Williams, 1990;Ekker et al, 1995;Stock et al, 1996;Amores et al, 1998;Vandepoele et al, 2004). cx35b has the highest similarity to mammalian Cx36 at the level of the primary sequence (Jabeen and Thirumalai, 2013), but the zebrafish genome contains at least three additional Cx36 orthologues. These additional orthologues may participate in the gap junctions that have been detected electrophysiologically between PMNs and between PMNs and VeLDs.…”