Expression of Lin28b leads to lymphopenia in transgenic mice. (A) Schematic of Vav expression vector used to generate transgenic mice. (B) Expression of the Lin28b transgene. Top panel: spliced transgenic Lin28b mRNA (arrowhead); the upper band seen in all transgenic tissues is due to amplification of unspliced, contaminating genomic DNA. Bottom panel: Actb used as a loading control. (C) Western blot for Lin28b protein in hematopoietic tissues of Lin28b mice. (D) Serial lymphocyte counts in the peripheral blood of WT and Lin28b-transgenic mice (n = 11). P < .01 for each time point. (E-F) Leukocyte subsets in peripheral blood (E; n = 5) and spleen (F; n = 3). M/G indicates myeloid cells that stain for the antigens Mac1 and Gr-1. (G-H) Percent of naive (CD62L⁺CD44⁻) and effector memory (CD62L⁻CD44⁺) CD4 (G) and CD8 (H) cells in peripheral blood from WT or Lin28b mice (n = 3). *P < .05; **P < .01; ***P < .001. WT is indicated by open circles or white bars; Lin28b, black squares or bars.