SECRETORY GLYCOPROTEINS OF THE SUBCOMMISSURAL ORGAN OF THE DOGFISH (SCYLIORHINUS-CANICULA) - EVIDENCE FOR THE EXISTENCE OF PRECURSOR AND PROCESSED FORMS

The subcommissural organ of the dogfish, Scyliorhinus canicula (L), ha s been investigated by use of antibodies and lectins applied to blots and tissue sections processed for light and electron microscopy. Antib odies have been raised against each of the bands that have previously been identified in immunoblots by the use of antisera raised against s ecretory glycoproteins ex tracted from the dogfish subcommissural orga n, viz., the 600-kDa band and two gel regions including the 475 to 400 -kDa and the 145-kDa bands obtained from preparative gels; they are re ferred to as Ab-600, Ab-475/400, and Ab-145. These antisera and the le ctins concanavalin A and wheat germ agglutinin have been used for the staining of: (1) blots of extracts of the dogfish subcommissural organ and optic tectum; (2) tissue sections of the dogfish brain. The findi ngs indicate that the bands of 600, 475 and 400 kDa contain compounds that should be regarded as secretory glycoproteins of the dogfish subc ommissural organ. The 600-kDa and 400-kDa bands are labeled by concana valin A; wheat germ agglutinin labels the 475-kDa band strongly and th e other two weakly. Ab-600 reacts with the bands at 600, 475 and 400 k Da and stains materials stored in the rough endoplasmic reticulum and secretory granules of 200-600 nm in diameter. The 600-kDa compound is probably a precursor form. Ab-475/400 stains the same three bands reve aled by Ab-600; immunocytochemically, it reacts with two types of secr etory granules (200-600 and 800-1200 nm in diameter) but it does not l abel the rough endoplasmic reticulum. Ab-145 reveals the bands at 600, 475 and 400 kDa and a diffuse zone in the region of 145 kDa; in light -microscopic immunocytochemistry, it behaves as Ab-475/400. The 475-kD a and 400-kDa glycoproteins, and a compound of approximately 145 kDa t hus probably correspond to processed forms. Ab-475/400 stains granules present in cell processes ending on local blood vessels and at the le ptomeninges. Since this antiserum selectively labels secretory granule s, this finding may be taken as evidence for a basal route of secretio n.