Transcriptional profiling of human and mouse nephron progenitor cells

Nephron endowment is determined by the self-renewal and induction of a nephron progenitor pool established at the onset of kidney development. In the mouse, the related transcriptional regulators Six1 and Six2 play non-overlapping roles in nephron progenitors. Transient Six1 activity prefigures, and is essential for, active nephrogenesis. In contrast, Six2 maintains later progenitor self-renewal from the onset of nephrogenesis. We compared Six2’s regulatory actions in mouse and human nephron progenitors by chromatin immunoprecipitation followed by DNA sequencing (ChIP-seq). Surprisingly, SIX1 was identified as a SIX2 target unique to the human nephron progenitors. Further, RNA-seq and immunostaining revealed overlapping SIX1 and SIX2 progenitor activity in the 16 week human fetal kidney. Human SIX1 ChIP-seq revealed a similar set of targets to SIX2, and predicted both factors bind DNA through an identical recognition site. In contrast to the mouse where Six2 binds its own enhancers but doesn’t interact with DNA around Six1, both human SIX1 and SIX2 bind homologous SIX2 enhancers and putative enhancers positioned around SIX1. Transgenic analysis of a putative human SIX1 enhancer in the mouse revealed a transient, mouse-like, pre-nephrogenic, Six1 regulatory pattern. Together, these data demonstrate a divergence in SIX-factor regulation between mouse and human nephron progenitors. In the human, an auto/cross-regulatory loop drives continued SIX1 and SIX2 expression during active nephrogenesis. In contrast, the mouse establishes only an auto-regulatory Six2 loop. It is tempting to speculate that differential SIX-factor regulation may contribute to species differences in the duration of progenitor programs and nephron output. Profiling of human and mouse nephron progenitor cells with mRNA-Seq; cells were purified from human and mouse embryonic kidneys with ITGA+ Ab or transgenic Cited1TagRPF