Localization of phosphatase inhibitor-1 mRNA in the developing and adult rat brain in comparison with that of protein phosphatase-1 mRNAs

Abstract

The localization and ontogenic changes in the gene expression for phosphatase inhibitor-1 (I-1) were analyzed by in situ hybridization histochemistry, and they were compared with those for three catalytic subunits of protein phosphatase type 1 (PP-1). At the adult stage, intense expression signals for I-1 were detected in the hippocampal formation, piriform cortex, claustrum, dorsal endopiriform cortex, suprachiasmatic nucleus, choroid plexus, arachnoid membrane, and pineal body. Moderate expression signals for I-1 were observed in the olfactory neuronal layers, caudate putamen, layers II-IV, and VI of the neocortex, and cerebellar granule cells, whereas the expression levels were low in the thalamus, cerebellar Purkinje cells, and brain stem nuclei. Although the expression levels for the three PP-1 mRNAs varied notably in various brain regions, a relatively high and parallel expression of I-1 and PP-1 mRNAs was found in most regions of the forebrain. However, the dissociation in the expression levels between I-1 and PP-1 mRNAs was found in several loci: the laminar expression of I-1 mRNA versus the homogeneous expression of PP-1 mRNAs in the cerebral cortex; low levels of expression of I-1 mRNA versus relatively high expression of PP-1 mRNAs in the brain stem nuclei; high expression of I-1 mRNA in the arachnoid membrane versus low expression of PP-1 mRNAs in it. The unparallel expression was also seen in embryonic brain: No significant expression of I-1 mRNA versus substantial expression of PP-1 mRNAs in the ventricular zone and cerebellar external granular layer; transiently high expression of I-1 mRNA in developing thalamus versus constantly moderate to low expression of PP-1 mRNAs there. These findings suggest that I-1 may play some discrete roles independent of the regulation of PP-1 in certain regions and developing stages of the brain.