Tlox tracking lymphocyte proliferation <i>in vivo</i>.

<p>(A) One-month old wild type, Tlox transgenic, Tlox and mb1Cre double transgenic mice were analyzed by gating on live T cells (TCRβ⁺) or B cells (B220⁺) from the spleen. tdTomato positive cells were highlighted by a region gate in the plots. (B) Bone marrow from Tlox and mb1Cre double transgenic mice was analyzed with CD43 and B220 markers. Pro-B, Pre-B and mature B cells were defined as CD43^hiB220^low, CD43^medB220^low and CD43^lowB220^hi, respectively, and are indicated in the FACS plot and the diagram below. Each fraction was analyzed for GFP and tdTomato expression with the tdTomato positive fraction marked in the plot. (C) Diagram and representative FACS plots of major stages of T cell development in the thymus and periphery. Red circle indicates cells undergoing proliferative expansion. The starting time for lckCre and CD4Cre expression around the DN3 stage are indicated by their relative position in the diagram. FACS analyses of tdTomato expression are displayed in sequential order according to stages of T cell development for the Tlox mice (upper panel), the Tlox and lckCre double transgenic mice (middle panel), and the Tlox and CD4Cre double transgenic mice (lower panel). <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003887#s2" target="_blank">Results</a> are representative of at least three mice for each genotype. DN3 cells are defined as CD4⁻CD8⁻CD44⁻CD25⁺, DN4 cells as CD4⁻CD8⁻CD44⁻CD25⁻, DP cells as CD4⁺CD8⁺, CD4 cells as CD4⁺CD8⁻, and CD8 cells as CD4⁻CD8⁺. DN cells also exclude any CD3, NK1.1, B220 and CD11b positive cells. (D) lckCre (upper panel) and CD4Cre (lower panel) mediated activation of the R26ZsGreen reporter during T cell development. Relative percentage of ZsGreen positive cells at each developmental stage is indicated in each plot. Shaded areas are relevant control populations from ZsGreen mice without a Cre transgene.