Zhang Q, Acland G M, Parshall C J, Haskell J, Ray K, Aguirre G D
The James A. Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Gene. 1998 Jul 30;215(2):231-9. doi: 10.1016/s0378-1119(98)00310-2.
Photoreceptor dysplasia (pd) is an autosomal recessive disease of miniature schnauzer dogs causing retinal degeneration. The disease is a homologue of retinitis pigmentosa, a group of genetically heterogeneous diseases, causing blindness in humans. A subtraction library was prepared from retinas of pd affected and age-matched normal control dogs to isolate de novo candidate genes for further examination. From the subtraction library, cDNA for phosducin (PDC), a member of the phototransduction pathway, was isolated as a transcript expressed at a higher level in the affected retina. First, the normal canine PDC cDNA was characterized to evaluate the PDC gene in the pd-affected retina. The characterized region of normal PDC cDNA spans 1258 nucleotides (nt) that include 738 nt of coding sequence predicted to encode a protein (Mr=28 209) of 245 amino acids (aa). Over the coding region, PDC shares 86-95% nt sequence identity and 90-95% identity in the deduced aa sequence with homologous mammalian sequences. A major transcript (1.9 kb) was observed only in retina by Northern analysis, but low levels of transcript were detected in brain, liver and kidney by reverse transcription and polymerase chain reaction. Retinal immunocytochemistry showed that PDC was detected only in rod photoreceptors, mainly in the inner segment and perinuclear region. By Northern blot analysis, increased PDC expression was observed in pre-degenerate affected retina relative to the age-matched normal. In pd- affected miniature schnauzer pedigree, a missense mutation was detected in codon 82 (CGA to GGA) that would create a non-conservative substitution (Arg to Gly) in close vicinity to the residue (Glu 85) which directly interacts with the betagamma-subunits of transducin. Only pd-affected dogs were found to be homozygous for the mutant allele, and none among 48 dogs tested from 20 other dog breeds had this allele, suggesting that the mutation could be causally associated with pd in miniature schnauzers. However, since some affected dogs are heterozygous for the mutant allele, and some are homozygous for the wild-type allele, this putative PDC missense mutation, if it is indeed a disease causing mutation, does not account entirely for the genetics of inherited retinal degeneration in the miniature schnauzer breed.
光感受器发育异常（pd）是一种导致视网膜变性的迷你雪纳瑞犬常染色体隐性疾病。该疾病是色素性视网膜炎的同源物，色素性视网膜炎是一组基因异质性疾病，可导致人类失明。从患有pd的犬和年龄匹配的正常对照犬的视网膜制备消减文库，以分离新的候选基因进行进一步研究。从消减文库中，分离出作为光转导途径成员的磷酸转导蛋白（PDC）的cDNA，作为在受影响视网膜中高水平表达的转录本。首先，对正常犬PDC cDNA进行表征，以评估pd受影响视网膜中的PDC基因。正常PDC cDNA的表征区域跨度为1258个核苷酸（nt），其中包括738 nt的编码序列，预计编码一个由245个氨基酸（aa）组成的蛋白质（Mr = 28209）。在编码区域，PDC与同源哺乳动物序列在核苷酸序列上具有86 - 95%的同一性，在推导的氨基酸序列上具有90 - 95%的同一性。通过Northern分析，仅在视网膜中观察到一个主要转录本（1.9 kb），但通过逆转录和聚合酶链反应在脑、肝和肾中检测到低水平的转录本。视网膜免疫细胞化学显示，仅在视杆光感受器中检测到PDC，主要在内段和核周区域。通过Northern印迹分析，相对于年龄匹配的正常犬，在预退化的受影响视网膜中观察到PDC表达增加。在患有pd的迷你雪纳瑞犬系谱中，在密码子82处检测到一个错义突变（CGA变为GGA），这将在紧邻与转导蛋白的βγ亚基直接相互作用的残基（Glu 85）处产生一个非保守性取代（Arg变为Gly）。仅发现患有pd的犬对突变等位基因是纯合的，并且从其他20个犬种测试的48只犬中没有一只具有该等位基因，这表明该突变可能与迷你雪纳瑞犬的pd有因果关系。然而，由于一些受影响的犬对突变等位基因是杂合的，而一些对野生型等位基因是纯合的，这种假定的PDC错义突变，如果它确实是一个致病突变，并不完全解释迷你雪纳瑞犬种遗传性视网膜变性的遗传学。
