The following antibodies were used in this study: PS1N and PS1C polyclonal antibodies were raised against PS1 N-terminal peptide (1–15 amino acids) and C-terminal peptide (455–467 amino acids), respectively, and APPC was raised against the last 15 amino acids of the human APP sequence. Mouse anti-PS1 loop monoclonal antibody was purchased from Chemicon (Temecula, CA). Anti-nicastrin antibody was raised against 688–708 amino acids of the protein and was available from Affinity BioReagents (Golden, CO). Anti-Aph1 and anti-Pen2 antibodies were from Zymed (San Francisco, CA), anti-b-catenin, anti-N-cadherin, and anti-glycogen synthase kinase 3b (GSK3b) were purchased from BD Transduction Laboratories (Lexington, KY), anti-cyclin-dependent kinase 5 (Cdk5) (C-8)
was from Santa Cruz Biotechnology (Santa Cruz, CA), and 6E10 monoclonal antibody was obtained from Signet Laboratories (Dedham, MA).