A radioimmunoassay for ependymins beta and gamma: two goldfish brain proteins involved in behavioral plasticity.

A radioimmunoassay (RIA) using 125I-labeled antigen was developed for the quantitative determination of two goldfish brain proteins (ependymins beta and gamma). The proteins were isolated from the cerebrospinal fluid (CSF) and cells of the ependymal zone surrounding goldfish brain ventricles. The turnover rates of beta and gamma were previously shown to be specifically enhanced after the animals successfully acquired a new pattern of swimming behavior. Femtomole quantities of ependymin beta were measurable by the RIA. In applications of the assay, beta and gamma ependymins were found to have common immunological properties, since 125I-beta-antigen bound to antibody could be displaced by unlabeled ependymin gamma as well as ependymin beta but not by a variety of other proteins including several purified glycoproteins isolated from goldfish brain. The ependymins were shown to constitute 14% of the total protein content of the brain extracellular fluid and also to be present as a minor component of the serum proteins (0.3%). Ependymins beta and gamma have an immunological reactivity in these fractions that can be increased by a factor of 30 on heating. The data suggest that the antigenicity of the molecules is highly masked, and that it may require some unraveling of the quaternary structure of the proteins before maximal interaction with the antisera becomes possible.