Notch3 is expressed early in thymocyte differentiation. (A) Gene expression as determined by microarray (Affymetrix U74Av2), where the global median (MAS5) is equal to 500. Only data for high-confidence probesets (at) are shown. Expression was statistically significant (MAS 5 detection call of Present) for all genes at all stages except for Hes1 in DP cells, as indicated by an asterisk. Expression of most Notch-related genes, including Notch3, peaks at the DN3 stage. (B) mAb staining of wild-type (solid line) or Notch3-mutant (dashed line) thymocytes; protein expression directly correlates with gene expression data, with the highest levels of expression on DN3 cells. Filled histograms represent isotype-matched control Ab staining on wild-type cells.