LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC IMMUNOCYTOCHEMICAL INVESTIGATION OF THE SUBCOMMISSURAL ORGAN USING A SET OF MONOCLONAL-ANTIBODIES AGAINST THE BOVINE REISSNERS FIBER

Ten monoclonal antibodies (Mabs) against glycoproteins of the bovine R eissner's fiber (RF) have been used in a structural and ultrastructura l immunocytochemical investigation of the bovine subcommissural organ (SCO) and RE The SCO of other vertebrate species has also been studied . For comparison, polyclonal anti bodies against bovine RF (AFRU) were used. The SCO and RF of ox, pig and dogfish and the SCO of dog, rabbi t, rat and frog were submitted to light-microscopic immunocytochemistr y using AFRU and Mabs. Postembedding ultrastructural immunocytochemist ry was applied to sections of bovine SCO using AFRU and Mabs. Bovine S CO consists of ependymal and hypendymal cell layers, the latter being arranged as cell strands across the posterior commissure, or as hypend ymal rosette-like structures. All cytoplasmic regions of the ependymal and hypendymal cells were strongly stained with AFRU. Six Mabs showed the same staining pattern as AFRU, one Mab stained RF strongly and SC O weakly, two Mabs stained RF but not SCO, and, finally, one Mab (3B1) exclusively stained the apices of the ependymal and hypendymal cells. All Mabs recognized the SCO and RF of the pig. Two Mabs bound to the SCO of the dog. One Mab stained the SCO of the rabbit and another the SCO of the rat. The SCO of frog and dogfish were totally negative. Bov ine SCO stained with AFRU, showed label in the rough endoplasmic retic ulum (RER) and the secretory granules (SG) of the ependymal and hypend ymal cells. The former, in the form of parallel cisternae, reticulum o r concentric rings, was seen throughout all cytoplasmic regions. SG we re abundant in the apical pole of the ependymal and hypendymal cells. Only one Mab showed a staining pattern similar to AFRU. Five Mabs show ed strong reactions in the SG but weak labeling of the RER. Mab 3B1 sh owed the label confined to the SG only. Our results suggest that: (i) in the bovine tissue, some epitopes are present in both precursor and processed materials, whereas others are characteristic of mature glyco proteins present in SG and the RF; (ii) the bovine SCO secretes at lea st two different compounds present in ependymal and hypendymal cells; (iii) both compounds coexist in the same secretory granule; (iv) there are conserved, class-specific, and species-specific epitopes in the g lycoproteins secreted by the SCO of vertebrates.