Expression of connexin genes in the human retina

Abstract

BackgroundGap junction channels allow direct metabolically and electrical coupling between adjacent cells in various mammalian tissues. Each channel is composed of 12 protein subunits, termed connexins (Cx). In the mouse retina, Cx43 could be localized mostly between astroglial cells whereas expression of Cx36, Cx45 and Cx57 genes has been detected in different neuronal subtypes. In the human retina, however, the expression pattern of connexin genes is largely unknown.MethodsNorthern blot hybridizations, RT-PCR as well as immunofluorescence analyses helped to explore at least partially the expression pattern of the following human connexin genes GJD2 (hCx36), GJC1 (hCx45), GJA9 (hCx59) and GJA10 (hCx62) in the human retina.ResultsHere we report that Northern blot hybridization signals of the orthologuous hCx36 and hCx45 were found in human retinal RNA. Immunofluorescence signals for both connexins could be located in both inner and outer plexiform layer (IPL, OPL). Expression of a third connexin gene denoted as GJA10 (Cx62) was also detected after Northern blot hybridization in the human retina. Interestingly, its gene structure is similar to that of Gja10 (mCx57) being expressed in mouse horizontal cells. RT-PCR analysis suggested that an additional exon of about 25 kb further downstream, coding for 12 amino acid residues, is spliced to the nearly complete reading frame on exon2 of GJA10 (Cx62). Cx59 mRNA, however, with high sequence identity to zebrafish Cx55.5 was only weakly detectable by RT-PCR in cDNA of human retina.ConclusionIn contrast to the neuron-expressed connexin genes Gjd2 coding for mCx36, Gjc1 coding for mCx45 and Gja10 coding for mCx57 in the mouse, a subset of 4 connexin genes, including the unique GJA9 (Cx59) and GJA10 (Cx62), could be detected at least as transcript isoforms in the human retina. First immunofluorescence analyses revealed a staining pattern of hCx36 and hCx45 expression both in the IPL and OPL, partially reminiscent to that in the mouse, although additional post-mortem material is needed to further explore their sublamina-specific distribution. Appropriate antibodies against Cx59 and Cx62 protein will clarify expression of these proteins in future studies.

Blood-Derived Human iPS Cells Generate Optic Vesicle–Like Structures with the Capacity to Form Retinal Laminae and Develop Synapses

“…Gap junctions are formed by a variety of connexins, but CX36 is perhaps the most important, particularly for transmission of the rod signal. 27,33,34 To our knowledge, this is the first report of CX36 expression in retinal progeny of human pluripotent stem cell cultures; however, the sparse distribution of CX36 plaques on RECOV-ERIN+ photoreceptor-like cells suggests that further maturation and/or changes in culture conditions are needed to fully promote gap junction formation in vitro. Even so, these data suggest that TiPSC-OV cultures may be useful for studying synapse development and/or generating donor retinal neurons capable of communicating with host cells following transplantation into the subretinal space.…”

Characterization of connexin36 gap junctions in the human outer retina

“…It has been shown that the human retina, similar to those of other mammalian species, expresses Cx36 both in the IPL and OPL (Söhl et al 2010), and the distribution of immunostained plaques resembled patterns found previously in the mouse, rabbit, rat and the monkey Mills et al 2001;Deans et al 2002;Kihara et al 2006Kihara et al , 2010O'Brien et al 2012;Kovács-Ö ller et al 2014). However, it has been difficult to obtain details on the GJ forming neurons of the human retina due to the postmortem decomposition of available tissue.…”

“…Cones have been shown to express Cx36 in various mammals including the monkey, rabbit, mouse, guinea pig (Raviola and Gilula 1973;Deans et al 2002;Feigenspan et al 2004;Lee et al 2003;O'Brien et al 2012) and humans (Söhl et al 2010). Some of these contacts have been shown to be functional GJs that allow for the electrical and tracer coupling of nearby cones (Schneeweis and Schnapf 1999;Li and DeVries 2004).…”

Identification of myopia-associated WNT7B polymorphisms provides insights into the mechanism underlying the development of myopia

“…Nevertheless, the precise mechanisms mediating the transduction of this defocus signal leading to myopia are still unclear. GJD2 is reportedly localized at the synapses between alpha-ganglion cells, AII amacrine cells, cone bipolar cells and photoreceptor cells [42][43][44][45][46][47][48][49][50][51] . Of all the interactions between these cells, the coupling between the amacrine cells and ganglion cells has been reported to be dramatically reduced in GJD2 knockout mice 52 .…”