Figure 3.

Thymocytes from mice with a gene-trapped Notch3 allele exhibit normal levels of cell death and cell proliferation. (A) Labeling of DNA strand breaks as an indicator of cell death, using dUTP and TdT (TUNEL). Control (C57BL/6) and Notch3^lacZ/lacZ mice showed indistinguishable levels of cell death (Student t test, P > .05) among total thymocytes (top), DN3 thymocytes (representing Notch3 peak expression, see Figure 1), or pre-DP thymocytes (the immediate progeny of Notch3-expressing DN3 cells). Statistics indicate mean ± SD for TUNEL⁺ cells in 3-5 independent experiments. (B) Cell-cycle status (DNA content, assessed by DAPI staining) in DN3 or pre-DP cells from control or Notch3^lacZ/lacZ thymuses; again, no significant differences could be distinguished (Student t test P > .05; statistics indicate mean ± SD for hyperdiploid cells in 5 or more independent experiments). Cell-cycle statistics include both TUNEL-negative cells from cell death experiments (A) and additional experiments where TUNEL was not performed, because there was no difference in the measured proliferative index with these 2 protocols.