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Subcellular localization of phosducin in rod photoreceptors

Published online by Cambridge University Press:  05 April 2005

JING CHEN ,
TATSURO YOSHIDA ,
KOICHI NAKANO  and
MARK W. BITENSKY
JING CHEN
Affiliation:
Department of Biomedical Engineering, College of Engineering, Boston University, Boston, MA 02215
TATSURO YOSHIDA
Affiliation:
Department of Biomedical Engineering, College of Engineering, Boston University, Boston, MA 02215
KOICHI NAKANO
Affiliation:
Department of Biomedical Engineering, College of Engineering, Boston University, Boston, MA 02215
MARK W. BITENSKY
Affiliation:
Department of Biomedical Engineering, College of Engineering, Boston University, Boston, MA 02215
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Abstract

Phosducin (Pd) is a 28-kD phosphoprotein whose expression in retina appears limited to photoreceptor cells. Pd binds to the β,γ subunits of transducin (Gt). Their binding affinity is markedly diminished by Pd phosphorylation. While Pd has long been regarded as a candidate for the regulation of Gt, the molecular details of Pd function remain unclear. This gap in understanding is due in part to a lack of precise information concerning the total amount and subcellular localization of rod Pd. While earlier studies suggested that Pd was a rod outer segment (ROS) protein, recent findings have demonstrated that Pd is distributed throughout the rod. In this report, the subcellular distribution and amounts of rat Pd are quantified with immunogold electron microscopy. After light or dark adaptation, retinal tissues were fixed in situ and prepared for ultrathin sectioning and immunogold labeling. Pd concentrations were analyzed over the entire length of the rod. The highest Pd labeling densities were found in the rod synapse. Less intense Pd staining was observed in the ellipsoid and myoid regions, while minimal labeling densities were found in the ROS and the rod nucleus. In contrast with rod Gt, no evidence was found for light-dependent movement of Pd between inner and outer segments. There is a relative paucity of Pd in the ROS as compared with the large amounts of Gt found there. This does not support the earlier idea that Pd could modulate Gt activity by controlling its concentration. On the other hand, the presence of Pd in the nucleus is consistent with its possible role as a regulator of transcription. The functions of Pd in the ellipsoid and myoid regions remain unclear. The highest concentration of Pd was found at the rod synapse, consistent with a suggested role for Pd in the regulation of synaptic function.

Keywords

PhosducinTransducinRodImmunogoldElectron microscopy
Type
Research Article
Information
Visual Neuroscience , Volume 22 , Issue 1 , January 2005 , pp. 19 - 25
Copyright
© 2005 Cambridge University Press

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