Regional and cellular localization of presenilin-2 RNA in rat and human brain.

In situ hybridization probes selective for presenilin-2 (PS-2) were used to determine the regional and cellular expression pattern of PS-2 mRNA in rat and human brain. In rat brain, the greatest expression of PS-2 mRNA is in the granule cell layers of the dentate gyrus and cerebellum. Molecular layers within these structures are virtually devoid of signal. Cortical expression of PS-2 message is restricted to neuronal layers, while the hybridization signal is weak or absent in molecular layers and white matter. Kidney, liver, and spleen display moderate levels of PS-2 message. A PS-2 sense strand probe produced no specific signals in any tissue. In human brain, the greatest hybridization signal for PS-2 is present in the granule cells of the cerebellum. Within hippocampus, the granule cell layer of dentate is strongly labeled, with CA3 pyramidal neurons also clearly visible. A laminar expression pattern is seen in the neuronal layers of human frontal and temporal cortex, with the deeper laminae having the strongest signals. These data are consistent with a primarily neuronal localization of PS-2 mRNA within the brains of both rat and human. Within the limitations of the analysis, it appears that virtually every neuron is labeled, and differences in the intensity of labeling are associated with both neuron size/density and brain region. The distribution of PS-2 RNA is not restricted to those regions having the greatest pathology in Alzheimer's disease. However, one unusual pathological feature of PS-2 mutations causing AD is the presence of cerebellar amyloid plaques in some cases. It is intriguing, in this context, that PS-2 RNA is enriched in the cerebellum, especially in human specimens.