A One‐Step Procedure for Isolation of Poly(A)+ mRNA from Isolated Brain Capillaries and Endothelial Cells in Culture

Abstract
The study of the regulation of low‐abundance blood‐brain barrier (BBB) transcripts either in isolated brain microvessels or in endothelial cells in tissue culture (ECL cells) requires isolation of poly(A)+ mRNA. Therefore, we describe here a single‐step method for isolation of polyfA)+ mRNA from brain capillaries or ECL cells using proteinase K/sodium dodecyl sulfate cell lysis and oligo‐de‐oxythymidine cellulose affinity chromatography. The yield of poly(A)+ mRNA was—15‐19 #g/g of brain or choroid plexus, 14‐17 μg per batch of isolated capillaries in a single bovine forebrain (190 g), and 6‐12 μg/107 ECL cells. Northern blot analysis showed characteristic and undegraded 2.1‐and 1.7‐kb actin transcripts in brain capillaries and a 2.1‐kb actin mRNA in brain and ECL cells. Northern analysis was also used to quantify the glucose transporter type I transcript, which is very rare in basal ECL cells, and this mRNA was shown to be up‐regulated by glucose deprivation. This method represents a significant improvement in the mRNA yield for brain capillaries or cultured endothelial cells compared with the conventional two‐step method.

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