Maintenance of low expression of p16^Ink4a in p190-B^−/− HSC/P during serial transplantation. p16 ^Ink4a, p21^Cip1, and p27^Kip1 expression of FL LSK cells and donor-derived BM LSK cells during serial transplantation. FL LSK cells and CD45.2⁺ BM LSK cells from primary and secondary transplantation recipients 4 months after transplantation were purified by FACS sorting and used for RNA preparation. The relative mRNA expression level of each gene was examined by quantitative real-time PCR and normalized to β-actin expression. Experiments were performed in triplicate and in 2 independent transplants (mean ± SD of the replicate).