The urothelium is a specialized epithelium that lines the urinary tract. It consists of three different cell types, namely, basal, intermediate and superficial cells arranged in relatively distinct cell layers. Normally, quiescent, it regenerates fast upon injury, but the regeneration process is not fully understood. Although several reports have indicated the existence of progenitors, their identity and exact topology, as well as their role in key processes such as tissue regeneration and carcinogenesis have not been clarified. Here we show that a minor subpopulation of basal cells, characterized by the expression of keratin 14, possesses self-renewal capacity and also gives rise to all cell types of the urothelium during natural and injury-induced regeneration. Moreover, these cells represent cells of origin of urothelial cancer. Our findings support the hypothesis of basally located progenitors with profound roles in urothelial homoeostasis.

Genome-wide association studies into complex immune-mediated diseases have indicated that many genetic factors, each with individual low risk, contribute to overall disease. It is therefore timely and important to characterise how immune responses may be subtly modified by tissue context. Here we explore the role of tissue-derived molecules in influencing the function of T-cells, which, due to their migratory nature, come into contact with many different microenvironments through their lifespan. Hedgehog (Hh) proteins act as secreted morphogens, providing concentration-dependent positional and temporal cell-fate specification in solid tissues. Hh signalling is required for embryogenesis and is important in postnatal tissue renewal and in malignancy. However, the function of Hh in dynamic, fluid systems such as in mammalian immunity is largely unknown. Here we show that Hh-dependent transcription in T-cells promoted Th2 transcriptional programs and differentiation, exacerbating allergic pathology. Interestingly, expression of Sonic Hedgehog (Shh) increased in lung epithelial cells following the induction of allergic disease, and lung T-cells upregulated Hh-target gene expression, indicating that T-cells respond to locally-secreted Hh ligands in vivo. We show that Il4, the key Th2 cytokine, is a novel transcriptional target of Hh signals in T-cells, providing one mechanism for the role of Hh in Th differentiation. We propose that Hh, secreted from inflamed, remodelling or malignant tissue can modulate local T-cell function. Our data present an unexpected and novel role for tissue-derived morphogens in the regulation of fluid immune responses, with implications for allergy and tumour responses, suggesting new uses for anti-Hh therapeutics.

Annexin-1 is a well-known endogenous anti-inflammatory protein that modulates the activation of cells of the innate immune system such as neutrophils and macrophages. We have recently reported a positive role for the exogenous protein on T cell differentiation, however, whether such a role holds true for the endogenous protein has yet to be determined. This aspect has been investigated here finding that Annexin-1-deficient T cells display an impaired activation and proliferation in response to anti-CD3 plus anti-CD28 stimulation. Furthermore, differentiation of T cells from Annexin-1-deficient mice in Th0/Th1/Th2 or Th17 skewing conditions demonstrated an increased Th2 phenotype compared to cells from control littermates. Similar results were obtained when we analyzed the Th1/Th2 profile of lymph node cells obtained from mice immunized with keyhole limpet hemocyanin or the inflammatory infiltrate in mouse model of allergic inflammation. These results demonstrate a novel modulatory role of endogenous Annexin-1 in TCR signaling and T cell differentiation and suggest this protein might play a dual and complementary role in the innate and adaptive immune response.

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