Complex expression pattern of the SCO-spondin gene in the bovine subcommissural organ: toward an explanation for Reissner's fiber complexity?

Bovine SCO-spondin is a glycoprotein secreted by the subcommissural organ (SCO), an ependymal derivative located in the roof of the third ventricle. It shows homology with developmental molecules involved in directional axonal growth. Using SCO-spondin cDNAs as probes, we analysed the specific expression of the corresponding gene in the bovine SCO by Northern blot and in situ hybridization (ISH). A strong expression was detected in the secretory ependymal and hypendymal cells of the SCO and the main transcripts showed a large size 14 kb. A single copy gene was revealed by Southern blot analysis of bovine genomic DNA. The presence of additional transcripts suggested a transcriptional regulation of the SCO-spondin gene. A comparative analysis of the results obtained by molecular and immunological techniques (immunoblotting and immunopurification) pointed to the presence of several SCO-spondin related proteins in the SCO encoded by the same gene. The presence in the cerebral hemispheres (CH) of a 54-kDa glycoprotein with a common epitope is discussed as a putative cleaved SCO-spondin product carried by the cerebrospinal fluid, that may act on neuronal development.