Journal of Neuroscience, Vol 5, 1023-1034, Copyright © 1985 by Society for Neuroscience
Membrane assembly in retinal photoreceptors. II. Immunocytochemical analysis of freeze-fractured rod photoreceptor membranes using anti- opsin antibodies
DM Defoe and JC Besharse
We have used a cytochemical technique for labeling freeze-fractured tissues
(Pinto da Silva, P., C. Parkison, and N. Dwyer (1981) Proc. Natl. Acad.
Sci. U.S.A. 78: 343-347) to examine the distribution of immunoreactive
opsin in rod photoreceptor membranes. Aldehyde-fixed retinas of African
clawed frogs (Xenopus laevis) embedded in a cross- linked protein matrix
were frozen and fractured at -196 degrees C, then thawed and labeled with
biotinylated sheep anti-cow opsin IgG followed by avidin-ferritin. In thin
sections of plastic-embedded retinas, rod outer segment (ROS) disc
membranes exposed by fracturing bound specific antibody intensely and
relatively uniformly. However, they differed from membranes of the inner
segment as well as those of erythrocytes in that protoplasmic face leaflets
did not assume an interrupted bilayer appearance and disc exoplasmic face
leaflets were apparently lost during thawing. The disposition of opsin
immunoreactivity in the cell membrane was highly asymmetric. Although ROS
plasma membranes from which discs are elaborated labeled heavily with
anti-opsin after cleavage, fractures passing along inner segment plasma
membranes bound very little antibody. In cross-fractures exposing inner
segment cytoplasm, we found specific labeling of Golgi complex elements, as
well as both perimitochondrial and periciliary vesicles. The latter are
presumed to be the vehicle shuttling newly synthesized membrane to the ROS
for disc assembly. These results suggest that opsin-containing membrane is
sorted out within the cell, being transported from synthetic sites to the
immediate periciliary zone where localized insertion into the cell membrane
takes place. Furthermore, the close correspondence of the present
immunocytochemical analysis with the distribution of opsin deduced from
prior quantitative freeze-fracture analysis (Besharse, J. C., and K. H.
Pfenninger (1980) J. Cell Biol. 87: 451-463) offers the possibility that
fracture-label may be generally useful for study of patterned membrane
topography in neuronal cells.