**Fewer immature T cells in ***Gata3* hypomorphic mutant embryos. (A) The absolute numbers of total thymocytes in *Gata3*^{g/g}, *Gata3*^{g/+}, and *Gata3*^{+/+} fetal thymi (7–20 mice of each genotype) were quantified. Data represent the summary of at least four independent experiments for each stage (means ± SEM). *, P < 0.01. (B) Thymocytes from e18.5 *Gata3*^{g/g} and *Gata3*^{+/+} embryos were analyzed for CD4 and CD8 surface expression. Data are representative of six to eight embryos of each genotype from five independent experiments. Numbers in boxed areas indicate the mean percentage of cells in those quadrants. (C) The absolute numbers of DN, DP, CD4 SP, CD8 SP, and γδTCR^{+} cells per thymus in e18.5 *Gata3*^{g/g}, *Gata3*^{g/+}, and *Gata3*^{+/+} embryos are shown. Data represent the summary of five independent experiments, and the mean of six to eight embryo in each genotype with SEM. *, P < 0.05. (D) The absolute number of DP cells per thymus in *Gata3*^{g/g} embryos compared with controls (both *Gata3*^{g/+} and *Gata3*^{+/+}) embryos. An average of two to six mice of each genotype were shown. (E) Surface expression of c-Kit and CD25 on Lin^{lo} thymocytes isolated from e15.5 and e18.5 *Gata3*^{g/g} and *Gata3*^{+/+} embryos. Data are representative of four to eight embryos of each genotype from at least two independent experiments for each stage. Numbers in the boxed areas indicate the mean percentage of cells in those sectors. (F) The absolute numbers of ETPs, DN2, DN3, and DN4 cells per thymus in e15.5 and e18.5 *Gata3*^{g/g}, *Gata3*^{g/+}, and *Gata3*^{+/+} embryos. Data represent the summary of at least two independent experiments for each stage and an average of four to eight embryos in each genotype with SEM. *, P < 0.05.

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