Immunohistochemical localization of La nuclear antigen in brain. Selective concentration of the La protein in neuronal nucleoli.

We analyzed the subcellular distribution of La antigen in brain tissue using 5 La antisera regarded as monospecific on the basis of immunofluorescence, counterimmunoelectrophoresis and Western blot studies. Staining patterns of these sera on human, rat and guinea pig brain were assessed by indirect immunofluorescence and immunoperoxidase methods. There was an intense staining of the nucleolus in most neurons exposed to the La antisera in guinea pig brain. Human cerebral cortical neurons as well as a subset of neurons of rat brain also showed nucleolar staining with the La antisera. This staining could be inhibited by preincubation of La antisera with immunopurified La protein. One- and two-dimensional analysis of the La antigen from soluble and nuclear extracts suggested that the soluble and nucleolar La antigens are the same protein. The concentration of La in the nucleolus may be related to the proposed processing activity of this protein for the RNA polymerase III transcript, 5S RNA.