Purification, characterization and developmental expression of rat brain PSP protein

We have isolated a perchloric acid-soluble protein designated as B-PSP1 from the postmitochondria supernatant fraction of rat brain. It was purified by gel filtration and anti-PSP1 affinity chromatography. Immunoblotting, peptide mapping, partial amino acid sequencing and reverse transcriptase-polymerase chain reaction showed that the amino acid sequence of B-PSP1 was identical with that of PSP isolated from rat liver. B-PSP1 was expressed in all regions including frontal cortex, posterior cortex, cerebellum, hippocampus, olfactory bulb, striatum, thalamus, midbrain, entorhinal cortex, pons, medulla and spinal cord. Immunohistochemical study showed that the expression of B-PSP1 was observed in ependymal cells of choroid plexus and glial cells of the other region. The expression of B-PSP1 in brain increased gradually from the first day to the 60th day of postnatal age, but the expression of B-PSP1 was slower than that of GFAP which is a marker protein of glial cells. The expression of PSP may be related to the cellular function rather than the developmental regulation of the glial cells. Thus, our findings are the first report on the presence of a PSP in rat brain which may be involved in the regulation of cellular function.