Id-1 and Id-2 are differentially expressed during cell cycle. Growth of FDCP1 cells was arrested in early G1 by isoleucine deprivation. After 36 hours, half the cells were transferred into normal growth medium (time = 0), with 25% WEHIcm as a complex source of cytokines (▪), while the other half were transferred into fresh medium without WEHIcm (▨). Cells were allowed to grow for 48 hours, during which time samples were removed for RNA isolation and northern hybridization to (A) Id-1 and (B) Id-2 probes. Signal intensity was quantitated by phosphorimage analysis before the blots were normalized by rehybridization to a 28S RNA oligonucleotide. Values were plotted as the relative intensity (pixel number) of the specific bands above background for each probe. Values are comparable only within the group of samples hybridized to a single probe; different exposure times were used for each probe to maximize clarity of the phosphorimage. (C) Cell cycle progression was monitored by 3H-thymidine uptake of the cytokine-replete, proliferating population.
(D) Raw data.
