Abstract
BackgroundChanges of the interneuronal coupling mediated by electrical synapse proteins in response to light adaptation and receptive field shaping are a paramount feature in the photoreceptor/horizontal cell/bipolar cell (PRC/HC/BPC) complex of the outer retina. The regulation of these processes is not fully understood at the molecular level but they may require information transfer to the nucleus by locally generated messengers. Electrical synapse proteins may comprise a feasible molecular determinant in such an information-laden signalling pathway.ResultsConnexin55.5 (Cx55.5) is a connexin with horizontal cell-restricted expression in zebrafish accumulating at dendritic sites within the PRC/HC/BPC complex in form of hemichannels where light-dependent plasticity occurs. Here we provide evidence for the generation of a carboxy-terminal domain of Cx55.5. The protein product is translated from the Cx55.5 mRNA by internal translation initiation from an in-frame ATG codon involving a putative internal ribosome entry site (IRES) element localized in the coding region of Cx55.5. This protein product resembling an 11 kDa domain of Cx55.5 is partially located in the nucleus in vivo and in vitro.ConclusionOur results demonstrate the generation of a second protein from the coding region of Cx55.5 by an IRES mediated process. The nuclear occurrence of a fraction of this protein provides first evidence that this electrical synapse protein may participate in a putative cytoplasmic to nuclear signal transfer. This suggests that Cx55.5 could be involved in gene regulation making structural plasticity at the PRC/HC/BPC complex feasible.
Highlights
Changes of the interneuronal coupling mediated by electrical synapse proteins in response to light adaptation and receptive field shaping are a paramount feature in the photoreceptor/horizontal cell/bipolar cell (PRC/HC/BPC) complex of the outer retina
BMC Molecular Biology 2008, 9:52 http://www.biomedcentral.com/1471-2199/9/52 connexins and/or processed connexin fragments may influence important biological functions like regulation of cell growth [1,2,3] and resistance to cell death [4] by mechanisms that do not require gap junction communication [5,6,7,8] but necessitate cytoplasm to nucleus signalling by locally generated messengers
Cx55.5 immunoreactivity in the nucleus of horizontal cells and identification of a candidate protein We have recently reported that Cx55.5 is exclusively expressed in HCs of the zebrafish retina
Summary
Changes of the interneuronal coupling mediated by electrical synapse proteins in response to light adaptation and receptive field shaping are a paramount feature in the photoreceptor/horizontal cell/bipolar cell (PRC/HC/BPC) complex of the outer retina. The regulation of these processes is not fully understood at the molecular level but they may require information transfer to the nucleus by locally generated messengers. BMC Molecular Biology 2008, 9:52 http://www.biomedcentral.com/1471-2199/9/52 connexins and/or processed connexin fragments may influence important biological functions like regulation of cell growth [1,2,3] and resistance to cell death [4] by mechanisms that do not require gap junction communication [5,6,7,8] but necessitate cytoplasm to nucleus signalling by locally generated messengers. Evidence for mechanisms that may play a similar role is entirely missing for electrical synapses
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