E foetal thymus by in situ hybridization [10]. However, DP thymocytes expressed

E foetal thymus by in situ hybridization [10]. However, DP thymocytes expressed the RET co-receptors Gfra1 and Gfra2, despite absence of Ret expression, and similarly, adult DN2? expressed Gfra1 but lacked PD1-PDL1 inhibitor 1 web significant Ret expression. This observation is in line with previous reports showing that GFRas are more abundantly expressed than RET [26,27], which suggests that GFRas may modulate RET signalling in a non-cell-autonomous manner (signalling in trans) [28,29]. Accordingly, we have recently shown that Lymphoid Tissue initiator cells use unconventional RET signalling in which receptor activation is provided by soluble ligand and co-receptors in trans secreted from nearby cells [17]. Thus, it is possible that RET negative, GFRa positive thymocytes may modulate the activity of neighbouring non-hematopoietic RET expressing cells. Analysis of adult conditional Ret mutant mice (Retfl/fl) bred to CD2Cre mice revealed a significant, but small impact on the absolute numbers of DN1 thymocytes. However, this reduction was not translated into consecutive developmental stages, indicating that RET mediated signals are dispensable to T cellFigure 3. Expression of Ret and its signalling partners in adult thymic populations. A. DN, DP, SPCD8+ and SPCD4+ thymocytes were purified by flow cytometry. Results show quantitative RT-PCR normalized to Hprt1. Error bars show s.e.. Results from three independent measurements are represented. B. RET expression in DN and DP thymocytes was determined by flow cytometry. RET: black bold line; Isotype control: grey line. C. Thymic DN, DP, SPCD8+ and SPCD4+ thymocytes and CD452 cells were purified by flow cytometry. Quantitative RT-PCR analysis was normalized to Hprt1. Error bars show s.e.. Results from three independent measurements are represented. D. DN1? and DN3? thymocytes were 18325633 purified by flow cytometry. Results show quantitative RT-PCR normalized to Hprt1. Error bars show s.e.. Results from three independent measurements are represented. doi:10.1371/journal.pone.0052949.gRET Signalling and T Cell DevelopmentFigure 4. Impact of Ret ablation in adult thymic development. 8 week old Ret conditional knockout hCD2Cre/Retnull/fl and control hCD2Cre2/ Retwt/fl mice were analyzed by flow cytometry. A. Left: representative flow cytometry analysis of CD42CD82CD32 thymocytes. Percentages are indicated. Right: Results show percentage of DN1-DN4 in hCD2Cre/Retnull/fl (open circle) and control hCD2Cre2/Retwt/fl (full circle) mice. Mean value: dash line. B. Left: representative flow cytometry analysis of CD4 versus CD8 expression profile. Percentages are indicated. Right: Results show percentage of DN, DP, SP4 and SP4 in hCD2Cre/Retnull/fl (open circle) and control hCD2Cre2/Retwt/fl (full circle) mice. Mean value: dash line. C. Proportion and absolute numbers of 18325633 purified by flow cytometry. Results show quantitative RT-PCR normalized to Hprt1. Error bars show s.e.. Results from three independent measurements are represented. doi:10.1371/journal.pone.0052949.gRET Signalling and T Cell DevelopmentFigure 4. Impact of Ret ablation in adult thymic development. 8 week old Ret conditional knockout hCD2Cre/Retnull/fl and control hCD2Cre2/ Retwt/fl mice were analyzed by flow cytometry. A. Left: representative flow cytometry analysis of CD42CD82CD32 thymocytes. Percentages are indicated. Right: Results show percentage of DN1-DN4 in hCD2Cre/Retnull/fl (open circle) and control hCD2Cre2/Retwt/fl (full circle) mice. Mean value: dash line. B. Left: representative flow cytometry analysis of CD4 versus CD8 expression profile. Percentages are indicated. Right: Results show percentage of DN, DP, SP4 and SP4 in hCD2Cre/Retnull/fl (open circle) and control hCD2Cre2/Retwt/fl (full circle) mice. Mean value: dash line. C. Proportion and absolute numbers of 1527786 cd TCR expressing thymocytes in hCD2Cre/Retnull/fl (open circle) and control hCD2Cre2/Retwt/fl (full circle) mice. Mean value: dash line. D. Absolute thymocyte numbers. Two-tailed student t-test analysis was performed between mutant and respective control mice. No statistically significant differences were found. doi:10.1371/journal.pone.0052949.gproduction in vivo. The co-expression of Ret/Gfra1 in DN1 and the decreased number of DN1 cells in Retfl/fl mice are consistent with a previous report indicating that GDNF promotes thymocyte survival in foetal thymic organ cultures (FTOCs) [11]. Neverthe-less, our data does not support a major role for this signalling axis in v.