Localization of olfactomedin-related glycoprotein isoform (BMZ) in the Golgi apparatus of glomerular podocytes in rat kidneys

A gene encoding olfactomedin-related glycoprotein was isolated from rat glo merulus despite its prior identification as a neuron-specific gene. The mRN A expression was remarkably intense in renal glomerulus and brain and faint in the lung and eye among rat systemic organs. Although the brain containe d four mRNA variants (AMY, AMZ, BMY, and BMZ) transcribed from a single gen e, the glomerulus, lung, and eye expressed only two variants (BMZ and BMY). The glycoprotein was intensely immunolocalized in glomerular podocytes and neurons by using an antibody against synthetic peptide of the M region, bu t weak in endothelial cells of the kidney and lung. Bronchiolar epithelial cells in the lung, and ciliary, corneal, and iris epithelial cells in the e ye were also stained. Immunogold electron microscopy revealed selective loc alization of olfactomedin-related glycoprotein at the Golgi apparatus in po docytes. In glomerular culture, the staining was also intense at a juxtanuc lear region in synaptopodin-positive epithelial cells of irregular shape (p henotypic feature of podocytes), whereas it was weak in synaptopodin-negati ve ones of cobblestone-like appearance (phenotypic feature of parietal epit helial cells of Bowman's capsule). Interestingly, Western blot analysis ide ntified an intense band corresponding to BMZ isoform and another faint band corresponding to BMY isoform in the glomerulus, whereas the intensity of t hese two bands were nearly equal in the lung and eye. In the brain, four ba nds corresponding to four isoforms were observed apparently. Computer seque nce analysis predicted coiled-coil structures in the secondary structure of the glycoprotein similar to those in Golgi autoantigens, suggesting signif icant roles in the unique functions of the Golgi apparatus in rat podocytes and neurons.