In contrast, the entire nephrogenic mesenchyme of Six2 mutants commits to nephron formation at the onset of kidney development, prematurely terminating the nephrogenic programme with only a small number of renal vesicles in place.[7, 8] Thus, Six2 has a unique regulatory activity among these factors: promoting the self-renewal of the nephron progenitor population. Self-renewal of nephron progenitors is normally opposed by Wnt signalling from
the adjacent branching tips of the ureteric epithelium. Here, Wnt9b is expressed in a graded fashion with GSK-3 beta pathway higher levels beneath the tips where induced mesenchyme cells first aggregate then epithelialize to generate renal vesicles, and at lower levels above the tip where the ureteric epithelium directly contacts the main body of the nephron progenitor pool. Wnt9b-directed canonical Wnt signalling mediated by a β-catenin containing transcriptional complex induces
renal vesicle formation. Together, these genetic-based data highlight a complex regulatory network underpinning Dabrafenib specification, maintenance, and commitment of nephron progenitors. What is not clear is how the transcriptional pathways direct these events. The majority of functional studies have examined gene knockouts to infer function rather than directly addressing the transcriptional networks at play. A combination of in vivo and in vitro analysis has defined regulatory modules, uncovering some of the basic networks underpinning Six2 regulation. However, a broader insight requires unbiased genome-scale methodology, integrating a full complement of the regulatory factors to take our understanding
to a deeper, systems level. Combining advances in next generation sequencing with chromatin immunoprecipitation-mediated GNA12 enrichment of transcriptional components at their target sites (ChIP-seq) has resulted in exciting new insights into critical control mechanisms regulating complex biological processes. Similarly, integrating ChIP-seq analysis with gene expression data in nephron progenitors is expected to lead to a new level of insight into transcriptional targets and modules of regulation, and to generate a clearer picture of how nephron progenitor status is programmed, maintained then lost on progenitor commitment to nephron fates. We have recently taken advantage of such experimental analyses to identify the gene regulatory networks engaged by Six2 and canonical Wnt-directed transcriptional complexes. Six2+ nephron progenitors were isolated from embryonic mouse kidneys and subjected to ChIP-seq either immediately (Six2 ChIP) or after treatment with a Wnt pathway agonist to induce β-catenin transcriptional engagement and epithelial commitment (β-catenin ChIP). While each factor was bound to an independent set of regulatory elements, a subset of genomic regions was directly engaged by both factors suggestive of overlapping regulatory functions.