Craft C M, Whitmore D H, Donoso L A
Department of Psychiatry, University of Texas Southwestern Medical School, Dallas 75235.
J Neurochem. 1990 Nov;55(5):1461-73. doi: 10.1111/j.1471-4159.1990.tb04927.x.
S-Antigen is a soluble cell protein unique to the retina and pineal gland. In the former, it is a well-characterized molecule that participates in light-induced signal transduction in photoreceptor cells. In the latter, the functional role is presently not known. The expression of S-antigen and its mRNA was examined in the rat retina and pineal gland throughout the diurnal cycle and with light interruption of the dark cycle. A cDNA for rat S-antigen was isolated from a pineal gland library to examine the mRNAs. A 1.7-kb mRNA for S-antigen was observed in both the pineal gland and the retina. Retinal S-antigen mRNA was expressed throughout the diurnal cycle and increased with light interruption of the dark cycle. In contrast, pineal gland S-antigen mRNA levels were detectable only during the dark and were absent preceding and during light. The phenotypic expression of immunoreactive S-antigen, identified with two S-antigen monoclonal antibodies (MAbs), MAb A9C6 and MAb C10C10, was analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel (PAGE) and isoelectric focusing (IEF) electrophoresis. Immunoblot analysis of gels after SDS-PAGE revealed a single 46-kDa protein in retina. In contrast, two bands of approximately 43 and 46 kDa were identified in the pineal gland. Immunoblots of the retinal extracts separated by IEF electrophoresis revealed five S-antigen isomers, which vary quantitatively throughout the diurnal cycle and when light interrupted the dark cycle. Immunoblots of the pineal gland samples separated by IEF electrophoresis indicated that the pineal gland possesses four pineal gland-specific forms of S-antigen in addition to the five forms present in the retina. The differences observed in the mRNA and protein analyses suggest tissue-specific structural components for S-antigen in the retina and pineal gland that are not regulated in the same manner.
S抗原是视网膜和松果体特有的一种可溶性细胞蛋白。在视网膜中，它是一种特性明确的分子，参与光感受器细胞中的光诱导信号转导。在松果体中，其功能作用目前尚不清楚。在大鼠视网膜和松果体中，对整个昼夜周期以及黑暗周期的光中断情况下S抗原及其mRNA的表达进行了检测。从松果体文库中分离出大鼠S抗原的cDNA以检测mRNA。在松果体和视网膜中均观察到一条1.7 kb的S抗原mRNA。视网膜S抗原mRNA在整个昼夜周期中均有表达，并随着黑暗周期的光中断而增加。相比之下，松果体S抗原mRNA水平仅在黑暗期间可检测到，在光照之前和期间不存在。用两种S抗原单克隆抗体（MAb），即MAb A9C6和MAb C10C10鉴定的免疫反应性S抗原的表型表达，通过十二烷基硫酸钠（SDS）-聚丙烯酰胺凝胶（PAGE）和等电聚焦（IEF）电泳进行分析。SDS-PAGE后凝胶的免疫印迹分析显示视网膜中有一条单一的46 kDa蛋白。相比之下，在松果体中鉴定出两条约43 kDa和46 kDa的条带。IEF电泳分离的视网膜提取物的免疫印迹显示有五种S抗原异构体，它们在整个昼夜周期以及黑暗周期的光中断时在数量上有所不同。IEF电泳分离的松果体样品的免疫印迹表明，除了视网膜中存在的五种形式外，松果体还具有四种松果体特异性的S抗原形式。在mRNA和蛋白质分析中观察到的差异表明，视网膜和松果体中S抗原的组织特异性结构成分的调控方式不同。
