Primary antibodies included anti-PCNA (1:500; Biomeda), -PH3 (1:500; Upstate), -AT8 and -AT100 (1:1000; Innogenetics), -PHF-1 (1:200; a generous gift from P. Davies), -AT180 (1:500; Innogenetics), -Tau (1:1 million; Dako), anti-phosphoS6kT398 (Drosophila-specific; Cell Signaling; 1:1000); anti-total S6K (C-terminal monoclonal; 1:500; a generous gift from G. Thomas); and anti-actin (20-66; Sigma; 1:50,000).