LOCALIZATION OF GUANYLATE CYCLASE ACTIVATING PROTEIN 2 IN MAMMALIAN RETINAS

当脊椎动物的眼睛暴露在光线下，然后光线熄灭时，神经视网膜中的视杆细胞必须重新建立暗适应状态。 这个过程中的关键步骤是鸟苷酸环化酶（GC）的细胞内刺激。 GC活化蛋白（GCAP 1和GCAP 2）调节GC活化。 GC的GCAP激活受细胞内钙离子[Ca 2 +]i浓度的调节。以往的研究发现GCAP 1定位于视杆细胞和视锥细胞的外节、胞体和突触终末。 在目前的研究中，我们使用原位杂交和免疫细胞化学定位GCAP 2在人类，猴子和牛视网膜。 在人和猴视网膜中，用抗GCAP 2抗体进行的最强烈的免疫标记在视锥内段、胞体和突触末梢中，并且在较小程度上在视杆内段和视网膜内神经元中。 在牛视网膜中，最强烈的免疫标记是在杆内段，与较弱的标记锥肌样细胞，胞体和突触。使用GCAP 2特异性抗体的其他酶促测定证实，GCAP 1，而不是GCAP 2，是刺激牛视杆外节GC的主要成分。 这些结果表明，虽然GCAP 1参与了在杆和锥外节GC的Ca 2 +-敏感的调节，GCAP 2可能在光感受器和内部视网膜神经元的非光转导功能。 虽然GCAP 1和GCAP 2突变在人类视网膜疾病中的作用尚未确定，但已知GC突变会导致称为Leber先天性黑蒙的严重视网膜病变。 GCAP功能缺失突变的个体可能会表现出相似的表型。

When the eyes of vertebrate animals have been exposed to light and then the light is extinguished, rod photoreceptors in the neural retina must re-establish a dark-adapted state. A critical step in this process is the intracellular stimulation of the enzyme guanylate cyclase (GC). GC-activating proteins (GCAP1 and GCAP2) modulate GC activation. GCAP activation of GC is regulated by the concentration of intracellular calcium ions [Ca2+]i. Previous studies have localized GCAP1 to rod and cone outer segments, somata and synaptic terminals. In the current study, we used in situ hybridization and immunocytochemistry to localize GCAP2 in human, monkey, and bovine retinas. In human and monkey retinas, the most intense immunolabeling with anti-GCAP2 antibodies was in the cone inner segments, somata and synaptic terminals and, to a lesser degree, in the rod inner segments and inner retinal neurons. In bovine retinas, the most intense immunolabeling was in the rod inner segments, with weaker labeling of cone myoids, somata and synapses. Additional enzymatic assays using a GCAP2-specific antibody confirmed that GCAP1, but not GCAP2, is the major component that stimulates GC in bovine rod outer segments. These results suggest that although GCAP1 is involved in the Ca2+-sensitive regulation of GC in rod and cone outer segments, GCAP2 may have non-phototransduction functions in photoreceptors and inner retinal neurons. Although the role of GCAP1 and GCAP2 mutations in human retinal diseases has yet to be established, mutations in GC are known to cause a severe retinopathy known as Leber's congenital amaurosis. Individuals with loss of function mutations in GCAPs might be expected to exhibit a similar phenotype.