Electrical synapses, or gap junctions, are widely
distributed in the vertebrate retina and are thought to
play critical roles in the transmission and coding of visual
signals. To investigate the molecular basis of this form
of neural communication in the retina, we have isolated,
characterized, and functionally expressed a cDNA for a
gap junction channel derived from the retina of the teleost
fish Danio aquipinnatus (giant danio). The cDNA
contained an open reading frame of 1146 nucleotides encoding
a connexin with a predicted molecular mass of 43.3 kDa
which shared extensive identity with Rattus norvegicus
Cx43 (78%). This protein (DACX43) contained several consensus
phosphorylation sequences in the c-terminal region, some
of which are conserved among Cx43 orthologs. RNA blot hybridization
revealed that DACX43 was expressed in the brain as well
as in the retina. In addition, Southern analysis suggested
that there are multiple copies of DACX43, or other closely
related sequences, in the Danio aquipinnatus genome.
When DACX43 was expressed by stable transfection in gap-junction-deficient
mouse N2A neuroblastoma cells, functional gap junctions
were formed as indicated by dual whole-cell recordings
of electrical coupling. We conclude that DACX43 is a connexin43
ortholog, which is expressed in the retina of Danio
aquipinnatus, and when translated is able to form
functional gap junction channels.