The vertebrate kidney plays an essential role in removing metabolic waste and balancing water and salt. This is carried out by nephrons, which comprise a blood filter attached to an epithelial tubule with proximal and distal segments. In zebrafish, two nephrons are first formed as part of the embryonic kidney (pronephros) and hundreds are formed later to make up the adult kidney (mesonephros). Previous studies have focused on the development of the pronephros while considerably less is known about how the mesonephros is formed. Here, we characterize mesonephros development in zebrafish and examine the nephrons that form during larval metamorphosis. These nephrons, arising from proliferating progenitor cells that express the renal transcription factor genes wt1b, pax2a, and lhx1a, form on top of the pronephric tubules and develop a segmentation pattern similar to pronephric nephrons. We find that the pronephros acts as a scaffold for the mesonephros, where new nephrons fuse with the distal segments of the pronephric tubules to form the final branching network that characterizes the adult zebrafish kidney.

Early thymic progenitors (ETPs) are endowed with diverse potencies and can give rise to myeloid and lymphoid lineage progenitors. How the thymic environment guides ETP commitment and maturation towards a specific lineage remains obscure. We have previously shown that ETPs expressing the heteroreceptor (HR) comprising IL-4 receptor alpha (IL-4Rα) and IL-13 receptor alpha 1 (IL-13Rα1) give rise to myeloid but not T cells. Here we show that signaling through the HR inhibits ETP maturation to the T cell lineage but enacts commitment towards the myeloid cells. Indeed, HR-positive ETPs (HR+ETPs), but not HR-negative ETPs (HR−ETPs), exhibit activated STAT6 transcription factor which parallels with downregulation of Notch1, a critical factor for T cell development. Meanwhile, myeloid-specific transcription factor, C/EBPα, usually under the control of Notch1 is up-regulated. Furthermore, in vivo inhibition of STAT6 phosphorylation restores Notch1 expression in HR+ETPs which regain T-lineage potential. In addition, upon stimulation with IL-4 or IL-13 HR−ETPs expressing virally transduced HR, also exhibit STAT 6 phosphorylation and down-regulation of Notch1 leading to inhibition of lymphoid but not myeloid lineage potential. These observations indicate that environmental cytokines play a role in conditioning ETP lineage choice which would impact T cell development.

Type 1 diabetes (T1D) manifests when the insulin-producing pancreatic beta-cells are destroyed as a consequence of an inflammatory process initiated by lymphocytes of the immune system. The non-obese diabetic (NOD) mouse develops T1D spontaneously and serves as an animal model for human T1D. The heteroreceptor (HR), comprising IL-4Rα and IL-13Rα1, serves both IL-4 and IL-13 cytokines which are believed to function as anti-inflammatory cytokines in T1D. However, whether the HR provides a responsive element to environmental (i.e. physiologic) IL-4/IL-13 in the regulation of peripheral tolerance and the development of T1D has yet to be defined. In this study, NOD mice deficient for the HR have been generated by means of IL-13Rα1 gene disruption and used to determine whether such deficiency affects the development of T1D. Surprisingly, the findings indicate that NOD mice lacking the HR (13R−/−) display resistance to T1D as the rise in blood glucose level (BGL) and islet inflammation were significantly delayed in these HR-deficient relative to HR-sufficient (13R+/+ ) mice. In fact, the frequency and spleen- to-pancreas dynamics of both Th1 and Th17 cells were affected in 13R−/− mice. This is likely due to an increase in the frequency of mTGFβ+FoxP3int Tregs and persistence of CD206+ macrophages in the pancreas as both types of cells confer resistance to T1D upon transfer to 13R+/+ mice. These findings reveal new insights as to the role environmental IL-4/IL-13 and the HR play in peripheral tolerance and the development of T1D.

Recently we reported that IL-4 and IL-13 signaling in murine early thymic progenitors (ETPs) expressing the heteroreceptor (HR) comprising IL-4 receptor alpha (IL-4Rα) and IL-13 receptor alpha 1 (IL-13Rα1) activate STAT6 and inhibit ETP maturation potential towards T cells. In this study we asked whether IL-4 and IL-13 signaling through the HR mobilizes other STAT molecules to shape ETP fate decision. The findings indicate that HR+ETPs undergoing cytokine signaling display increased STAT1, but not STAT3, phosphorylation in addition to STAT6 activation. In parallel, the ETPs had a STAT1-dependent heightened expression of IRF-8, a transcription factor essential for development of CD8α+ dendritic cells (DCs). Interestingly, STAT1 phosphorylation and IRF-8 upregulation which were independent of STAT6 activation guided ETP maturation towards myeloid cells with a CD8α+ DC phenotype. Furthermore, these CD8α+ DCs display a thymic resident phenotype as they did not express SIRPα, a molecule presumed to be involved in cell migration. These findings suggest that IL-4 and IL-13 cytokine-induced HR signaling provides a double-edged sword that simultaneously blocks T cell lineage potential but advances myeloid maturation which could impact T cell selection and central tolerance.

IL-4 and IL-13 have been defined as anti-inflammatory cytokines which can counter myelin-reactive T cells and modulate experimental allergic encephalomyelitis (EAE). However, it is not known whether endogenous IL-4 and IL-13 contribute to the maintenance of peripheral tolerance and whether their function is coordinated with T regulatory cells (Tregs). Here, we utilized mice in which the common cytokine receptor for IL-4 and IL-13, namely the IL-4Rα/IL-13Rα1 heteroreceptor (HR), is compromised and determined whether the lack of signaling by endogenous IL-4 and IL-13 through the HR influences the function of effector Th1 and Th17 cells in a Treg-dependent fashion. The findings indicate that mice-deficient for the HR (13R-/-) are more susceptible to EAE than mice sufficient for the HR (13R+/+) and develop early onset and more severe disease. Moreover, Th17 cells from 13R-/- mice had reduced ability to convert to Th1 cells and displayed reduced sensitivity to suppression by Tregs relative to Th17 effectors from 13R+/+ mice. These observations suggest that IL-4 and IL-13 likely operate through the HR and influence Th17 cells to convert to Th1 cells and to acquire increased sensitivity to suppression leading to control of immune-mediated central nervous system inflammation. These previously unrecognized findings shed light on the intricacies underlying the contribution of cytokines to peripheral tolerance and control of autoimmunity.