Fig. 3. Telencephalon-specific Rb deficiency does not produce widespread apoptosis. (A) To detect cell death, E13.5 conditional mutant and control littermates, as well as germline Rb knockouts, were sectioned (coronal) and assayed for TUNEL labeling. Unlike whole-embryo Rb knockouts (c), conditional Rb mutants (b) did not exhibit massive neuronal apoptosis. However, in the telencephalon, TUNEL-positive cells in the conditional mutant (b) were slightly higher than controls (a), with 79.7 ± 14.0 and 51.0 ± 4.7 cells/section, respectively (B). Cell death was examined further in later stage embryos (E15.5, 16.5, 17.5 and 19.5), with no detectable apoptosis over littermate controls (d and e). (n = 5). Error bars denote standard error. Bar = 100 µm.