A critical role of CaBP4 in the cone synapse.
OBJECTIVE
CaBP4, a photoreceptor-specific protein of the rods and cones, is essential for the development and maintenance of the mouse photoreceptor synapse. In this study, double CaBP4/rod alpha-transducin knockout (Cabp4(-/-)Gnat1(-/-)) mice lacking the rod-mediated component of electrophysiologic responses were generated and analyzed to investigate the role of CaBP4 in cones.


METHODS
The retinal morphology and physiologic function of 2-month-old Cabp4(-/-)Gnat1(-/-) mice were analyzed using immunocytochemistry, electron microscopy, and single-flash and flicker electroretinography (ERG).


RESULTS
The thickness of the outer plexiform layer and the number of photoreceptor terminals in Cabp4(-/-)Gnat1(-/-) mice were reduced to levels similar to those of Cabp4(-/-) mice. Single-flash and flicker ERG showed that the amplitude and sensitivity of the b-wave in the Cabp4(-/-)Gnat1(-/-) mice were severely attenuated compared with those in wild-type and Gnat1(-/-) mice.


CONCLUSIONS
Results indicate that the cone synaptic function in Cabp4(-/-)Gnat1(-/-) mice was severely disrupted, whereas the morphologic defects observed in Cabp4(-/-)Gnat1(-/-) mice were similar to those of single Cabp4(-/-) knockout mice. This and a previous study reveal that CaBP4 is critical for signal transmission from rods and cones to second-order neurons.
Maeda
Tadao
T
Department of Ophthalmology, University of Washington, Seattle, 98195, USA.
Lem
Janis
J
Palczewski
Krzysztof
K
Haeseleer
Françoise
F
D000818:Animals; D002135:Calcium-Binding Proteins / Q000502:physiology*; D004596:Electroretinography; D005136:Eye Proteins / Q000502:physiology*; D019084:Fluorescent Antibody Technique, Indirect; D005838:Genotype; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000502:physiology*; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology* / Q000648:ultrastructure; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D015293:Transducin / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology
C494133:Cabp4 protein, mouse; D002135:Calcium-Binding Proteins; D005136:Eye Proteins; D009419:Nerve Tissue Proteins; D015293:Transducin