No abstract

While nephron formation is known to be initiated by a mesenchyme-to-epithelial transition of the cap mesenchyme to form a renal vesicle (RV), the subsequent patterning of the nephron and fusion with the ureteric component of the kidney to form a patent contiguous uriniferous tubule has not been fully characterized. Using dual section in situ hybridization (SISH)/immunohistochemistry (IHC) we have revealed distinct distal/proximal patterning of Notch, BMP and Wnt pathway components within the RV stage nephron. Quantitation of mitoses and Cyclin D1 expression indicated that cell proliferation was higher in the distal RV, reflecting the differential developmental programs of the proximal and distal populations. A small number of RV genes were also expressed in the early connecting segment of the nephron. Dual ISH/IHC combined with serial section immunofluorescence and 3D reconstruction revealed that fusion occurs between the late RV and adjacent ureteric tip via a process that involves loss of the intervening ureteric epithelial basement membrane and insertion of cells expressing RV markers into the ureteric tip. Using Six2-eGFPCre x R26R-lacZ mice, we demonstrate that these cells are derived from the cap mesenchyme and not the ureteric epithelium. Hence, both nephron patterning and patency are evident at the late renal vesicle stage.

Lineage conversion of one somatic cell type into another constitutes an attractive approach for research and clinical use. Lineage conversion can proceed in a direct manner, in the absence of proliferation and multipotent progenitor generation, or in an indirect manner, by the generation of expandable multipotent progenitor states. Here we report on the development of a combined reprogramming methodology that, transitioning through a plastic intermediate state, allows for the generation of human mesodermal progenitor cells while circumventing the traditional hallmarks of pluripotency. Converted mesodermal progenitor cells demonstrated bi-potent differentiation potential and were able to generate endothelial and smooth muscle lineages. Importantly, human fibroblasts can be converted into angioblast-like progenitor cells by non-integrative approaches. Differentiated angioblast-like cells exhibit neo-angiogenesis and anastomosis in vivo. The methodology for indirect lineage conversion to angioblast-like cells described here adds to the armamentarium of reprogramming approaches aimed at the clinical treatment of ischemic pathologies.