Expression of sphingolipid activator protein gene in brain and systemic organs of developing mice.

The sphingolipid activator proteins (SAPs) are a family of small, heat-stable glycoproteins, proven or postulated to be required for in vivo degradation of some sphingolipids by hydrolytic enzymes. Four of them are coded by a single gene, which generates a transcript including the four saps in tandem. The large translation product is then proteolytically cleaved to generate individual saps. A hypothesis has been advanced that the large sap-precursor protein might by itself have functions distinct from the processed individual saps. Expression of the gene in the brain regions and other organs of 9-, 20- and 60-day-old mice was examined by Northern blot analysis. It was expressed in all tissues and organs examined. However, the expression level was higher in the nervous system than in systemic organs. The level of sap expression remained constant in several regions of the nervous system, and in the systemic organs decreased from 9 to 60 days, particularly in the heart and kidney. In situ hybridization analysis indicated that while the transcript was found throughout the adult mouse brain, the epithelial cells of the choroid plexus showed the highest expression level, followed by various gray matter areas, including cortex and hippocampus. Generally, the mRNA was associated with neuronal perikarya rather than neuropiles or glial cells. This regional distribution was similar at the ages examined.