Visual Neuroscience



Rho GTPases regulate rhabdom morphology in octopus photoreceptors


ARIA M.  MILLER  a1 , TERESA  RAMIREZ  a1 , FREDDI I.  ZUNIGA  a2 , GINA H.  OCHOA  a1 , SHAUNTE  GRAY  a1 , SHANNON D.  KELLY  a1 , BRIAN  MATSUMOTO  a3 and LAURA J.  ROBLES  a1 c1
a1 Department of Biology, California State University, Dominguez Hills, Carson
a2 Department of Chemistry, California State University, Dominguez Hills, Carson
a3 Neuroscience Research Institute, University of California, Santa Barbara

Article author query
miller am   [Google Scholar] 
ramirez t   [Google Scholar] 
zuniga fi   [Google Scholar] 
ochoa gh   [Google Scholar] 
gray s   [Google Scholar] 
kelly sd   [Google Scholar] 
matsumoto b   [Google Scholar] 
robles lj   [Google Scholar] 
 

Abstract

In the cephalopod retina, light/dark adaptation is accompanied by a decrease/increase in rhabdom size and redistribution of rhodopsin and retinochrome. Rearrangements in the actin cytoskeleton probably govern changes in rhabdom size by regulating the degradation/formation of rhabdomere microvilli. Photopigment movements may be directed by microtubules present in the outer segment core cytoplasm. We believe that rhodopsin activation by light stimulates Rho and Rac signaling pathways, affecting these cytoskeletal systems and their possible functions in controlling rhabdom morphology and protein movements. In this study, we localized cytoskeletal and signaling proteins in octopus photoreceptors to determine their concurrence between the lighting conditions. We used toxin B from Clostridium difficile to inhibit the activity of Rho/Rac and observed its effect on the location of signaling proteins and actin and tubulin. In both lighting conditions, we found Rho in specific sets of juxtaposed rhabdomeres in embryonic and adult retinas. In the light, Rho and actin were localized along the length of the rhabdomere, but, in the dark, both proteins were absent from a space beneath the inner limiting membrane. Rac colocalized with tubulin in the outer segment core cytoplasm and, like Rho, the two proteins were also absent beneath the inner limiting membrane in the dark. The distribution of actin and Rho was affected by toxin B and, in dark-adapted retinas, actin and Rho distribution was similar to that observed in the light. Our results suggest that the Rho/Rac GTPases are candidates for the regulation of rhabdomere size and protein movements in light-dark-adapted octopus photoreceptors.

(Received August 26 2004)
(Accepted February 24 2005)


Key Words: Retina; Cytoskeleton; Actin; Microtubules; Rho.

Correspondence:
c1 Address correspondence and reprint requests to: Laura J. Robles, Department of Biology, California State University, Dominguez Hills, 1000 East Victoria Street, Carson, CA 90747, USA. E-mail: lrobles@csudh.edu