IRES-mediated translation of the carboxy-terminal domain of the horizontal cell specific connexin Cx55.5 in vivo and in vitro.
BACKGROUND
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. Electrical synapse proteins may comprise a feasible molecular determinant in such an information-laden signalling pathway.


RESULTS
Connexin55.5 (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.


CONCLUSIONS
Our 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.
Ul-Hussain
Mahboob
M
Department of Neuroanatomy and Molecular Brain Research, Ruhr-University Bochum, University Street 150, D-44801 Bochum, Germany. hussainjnu@yahoo.com
Zoidl
Georg
G
Klooster
Jan
J
Kamermans
Maarten
M
Dermietzel
Rolf
R
D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D017630:Connexins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D011401:Promoter Regions, Genetic / Q000235:genetics; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D015027:Zebrafish
D017630:Connexins; D020033:Protein Isoforms; D008156:Luciferases