Carboxypeptidase E knockout mice have abnormal retinal function

Abstract

Abstract: : Purpose: To identify potential functional partners of cone arrestin, we performed a yeast two–hybrid screen using mouse cone arrestin (mCAR) as bait on a mouse retinal library made with either light– or dark–adapted mouse retinas. Eight independent clones of carboxypeptidase E (CPE) were identified from the dark library. To characterize this interaction, we determined the mRNA expression and protein distribution of CPE in the mouse retina. We also tested retinal function of the CPE knockout mice. Methods: Northern blot analysis was used to study mRNA expression of CPE in selected mouse tissues, and immunonocytochemistry was used to determine the distribution of CPE in the mouse retina. Retinal morphology was observed by light and electronic microscope (EM). Retinal function was analyzed by electroretinogram (ERG) recording of the CPE knockout (KO) mice and their littermate controls. Results: CPE has the highest expression in the retina and olfactory among the tissues tested by Northern blot analysis. Immunocytochemistry shows that CPE is localized in both rod and cone photoreceptors, as well as in the inner retina and ganglion cells, in either light– or dark–adapted mice. CPE knockout mice have normal retinal morphology either under light microscope or under EM; however, they have abnormal ERG responses, compared to their littermate controls. CPE KO animals at 15–week–old appear to have reduced rod response sensitivity and a longer b wave implicit time. At age 30 weeks, the dark–adapted ERG of the CPE KO animals has a greatly reduced b wave amplitude, which originates from the inner retina. Conclusions: The high expression levels of CPE in retina and olfactory suggest that it may play an important role in these sensory organs. Our preliminary ERG results from the CPE KO mice suggest that CPE may participate in the synaptic flow of information from the photoreceptors to the inner retina. Whether the ERG changes are a direct result of the CPE KO in the retina, or the effect of anesthesia on CPE KO mice is still to be elucidated.

Keywords: retina • photoreceptors • protein structure/function