The secretory material of the subcommissural organ of the chick embryo. Characterization of a specific polypeptide by two-dimensional electrophoresis.

The subcommissural organ (SCO) is a cerebral gland that releases into the cerebrospinal fluid a carbohydrate-rich glycoprotein which condenses to form Reissner's fiber (RF). Western blots from two-dimensional gel electrophoresis were stained with lectins (Concanavalin-A, wheat germ agglutinin) and anti-bovine RF serum to identify the secretory products of the chick embryo SCO. Immunohistochemical investigations showed that the anti-bovine RF serum reacted exclusively with the secretion of the SCO. Comparative protein patterns of SCO, pineal organ and cerebral hemisphere extracts allowed us to characterize a specific polypeptide in the SCO electrophoretic profiles. The polypeptide was a highly acid compound (isoelectric point of 4.7) with a high molecular weight (390 kDa). On Western blots only this component was immunoreactive with the RF antiserum and it exhibited an affinity for the two lectins. On the basis of these results, this polypeptide may be considered as a specific component of the secretory material synthesized by the SCO cells of the chick embryo.