May 2004
Volume 45, Issue 13
ARVO Annual Meeting Abstract  |   May 2004
Distribution of fusion regulators in photoreceptor cells.
Author Affiliations & Notes
  • D. Deretic
    Surgery/Ophthalmology, Cell Biology and Physiology,
    University of New Mexico, Albuquerque, NM
  • A. Williams
    Program in Biochemistry,
    University of New Mexico, Albuquerque, NM
  • N. Ransom
    University of New Mexico, Albuquerque, NM
  • Footnotes
    Commercial Relationships  D. Deretic, None; A. Williams, None; N. Ransom, None.
  • Footnotes
    Support  EY 12421
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 2440. doi:
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      D. Deretic, A. Williams, N. Ransom; Distribution of fusion regulators in photoreceptor cells. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2440.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract: : Purpose: In retinal photoreceptors rhodopsin–bearing transport carriers (RTCs) dock and fuse in the proximity of the connecting cilium. The specific fusion site on the rod inner segment (RIS) plasma membrane has not been well characterized. We have previously shown that the small GTPase rab8 regulates tethering and fusion of RTCs, in conjunction with PI(4,5)P2, moesin, actin and rac1. In epithelial cells, rab8 regulates fusion with the plasma membrane containing SNARE Syntaxin 4, at the sites marked by the octameric membrane–tethering Sec6/8 complex. In the present study, we wanted to determine the distribution of these fusion regulators in photoreceptor cells. Methods: Frog retinas were subjected to subcellular fractionation followed by immunoblotting, or examined by confocal microscopy using specific antibodies. Results: We determined the distribution of Syntaxin 4 and Syntaxin 3 (found in the basolateral and the apical plasma membrane of epithelial cells, respectively), among retinal subcellular fractions separated on sucrose density gradients. These fractions were also probed with an antibody to the ß2 subunit of Na,K–ATPase, a marker found exclusively in the RIS plasma membrane, between the base of the connecting cilium and the outer limiting membrane (OLM). The distribution of Na,K–ATPase paralleled that of Syntaxin 3. We performed confocal microscopy on control and nocodazole treated retinas, since in epithelial cells the disruption of microtubules causes depolarization of Syntaxin 3. Immunoreactivity of Syntaxin 3, observed along the RIS plasma membrane in control cells, appeared to be decreased in nocodazole treated retinas. Antibody to Sec8 revealed partial colocalization of this component of the membrane–tethering complex with the small GTPase rab8. Conclusions:Our data suggest that Syntaxin 3 and Sec6/8 complex may be involved in docking and fusion of RTCs in photoreceptor cells.

Keywords: photoreceptors • cell membrane/membrane specializations • opsins 

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