DAPT upregulates cdk5 expression at the transcriptional level. E18 rat embryonic cortical neurons were cultured for 7 d in B27/neurobasal medium and then treated with either DMSO or 10 μM DAPT. Total RNA was isolated from the neurons and RT-PCR was performed using the First Strand cDNA synthesis Kit (Roche, USA). Transcript levels of cdk5, p35, and Notch-responsive genes, neurogenin (Ngn), and Hes1 are shown. GAPDH transcript levels are shown as controls. The data represent one of three separate experiments. (A) Semi-quantitative RT-PCR analyses show changes in transcript levels of the various genes as indicated in neurons at 24 h of DAPT treatment (+) as compared to the DMSO-tretaed control (-). (B) Quantitative PCR analyses show the relative levels of cdk5 mRNA expression in DMSO- and DAPT-treated neurons from 12 h to 48 h of treatment. (C) Semi-quantitative RT-PCR analyses show the expression of indicated genes in the neurons treated with DAPT from 0 - 48 h of treatment.