Nakajima T, Walkup R D, Tochigi A, Shearer T R, Azuma M
Senju Laboratory of Ocular Sciences, Senju Pharmaceutical Co., Ltd., Kobe, Hyogo 650-0047 Japan.
Exp Eye Res. 2007 Nov;85(5):651-8. doi: 10.1016/j.exer.2007.07.019. Epub 2007 Aug 6.
Lacritin is a mitogen of human salivary gland cells as well as a stimulator of human corneal epithelial cells. It is expected to be an important factor in maintaining the surrounding ocular surface. The monkey would be a relevant animal model in which to study the role of lacritin in ophthalmic physiology and pathology. However, to our knowledge, no cDNA cloning or functional analysis of monkey lacritin has been performed. Thus, the purposes of this study were: (1) to clone the monkey ortholog of lacritin; (2) to characterize lacritin in tears from several species; and (3) to determine the tissues where lacritin is produced and secreted. cDNA for lacritin from rhesus macaque contained 547 bp, with 411 bp in an open reading frame (ORF) encoding a protein of 137 amino acids. Monkey lacritin showed 89% amino acid homology with human lacritin; one amino acid was deleted in all three monkey strains. The predicted MW of mature lacritin was 12.2 kDa, and the isoelectric point was 4.99. Lacritin showed anomalous migration at approximately 21.0 kDa on SDS-PAGE, as confirmed by immunoblotting and amino acid sequencing. Similar to native lacritin in monkey tears, a 21 kDa band was also detected in human tears. In contrast, no lacritin was observed at a similar position on SDS-PAGE in rat, rabbit and dog tears. In the monkey, lacritin mRNA was expressed highly in the lacrimal gland, moderately in the conjunctiva and the meibomian gland, and weakly in corneal epithelium. In primates, lacritin was produced in the lacrimal gland and secreted into tear fluid. These results suggest that lacritin might be important for the maintenance of the ocular surface in higher animals, such as monkeys and humans.
乳铁蛋白是人类唾液腺细胞的有丝分裂原，也是人类角膜上皮细胞的刺激物。它有望成为维持眼表环境的重要因素。猴子将是研究乳铁蛋白在眼科生理学和病理学中作用的相关动物模型。然而，据我们所知，尚未对猴乳铁蛋白进行cDNA克隆或功能分析。因此，本研究的目的是：（1）克隆猴乳铁蛋白的直系同源基因；（2）鉴定几种物种眼泪中的乳铁蛋白；（3）确定产生和分泌乳铁蛋白的组织。恒河猴乳铁蛋白的cDNA包含547bp，其中411bp位于开放阅读框（ORF）中，编码一个由137个氨基酸组成的蛋白质。猴乳铁蛋白与人乳铁蛋白的氨基酸同源性为89%；在所有三种猴品系中均缺失一个氨基酸。成熟乳铁蛋白的预测分子量为12.2kDa，等电点为4.99。经免疫印迹和氨基酸测序证实，乳铁蛋白在SDS-PAGE上约21.0kDa处出现异常迁移。与猴眼泪中的天然乳铁蛋白类似，在人眼泪中也检测到一条21kDa的条带。相比之下，在大鼠、兔子和狗的眼泪中，在SDS-PAGE的相似位置未观察到乳铁蛋白。在猴子中，乳铁蛋白mRNA在泪腺中高表达，在结膜和睑板腺中中度表达，在角膜上皮中弱表达。在灵长类动物中，乳铁蛋白在泪腺中产生并分泌到泪液中。这些结果表明，乳铁蛋白可能对维持猴子和人类等高等动物的眼表很重要。
