DROSHA and central nervous system cancer: HnRNPA1 binds to the conserved terminal loop of pri-let-7a-1 and blocks its processing by Drosha.[14] To determine whether hnRNPA1 can repress let-7a biogenesis in glioma cells, we designed specific primers to detect either the upstream region or the pri-let-7a-1 stem loop structure (Fig. 6A).