Project description:The vertebrate Six1 and Six2 arose by gene duplication from the Drosophila so (sine oculis) and have since diverged in their developmental expression patterns. Both genes are expressed in nephron progenitors of human fetal kidneys, and mutations in SIX1 or SIX2 cause branchio-oto-renal or renal hypodysplasia respectively. Since ~80% of SIX1 target sites are shared by SIX2, it is speculated that SIX1 and SIX2 may be functionally interchangeable by targeting common downstream genes. In contrast, in mouse kidneys, the expression of Six1 and Six2 only transiently overlaps in the metanephric mesenchyme before the onset of ureteric branching, and only Six2 expression is maintained in the nephron progenitors throughout development. This non-overlapping expression between Six1 and Six2 in mouse nephron progenitors promoted us to examine if Six1 can replace Six2. Surprisingly, forced expression of Six1 failed to rescue Six2-deficient kidney hypoplasia. We found that Six1 mediated Eya1 nuclear translocation and inhibited premature epithelialization of the progenitors but failed to rescue the proliferation defects and cell death caused by Six2-knockout. Genome-wide binding analyses showed that Six1 only bound to a small subset of Six2 target sites, but many Six2-bound loci that are crucial to the renewal and differentiation of nephron progenitors lacked Six1 occupancy. Thus, these data indicate that Six1 cannot substitute Six2 to drive nephrogenesis in mouse kidneys, demonstrating that these two transcription factors have not maintained equivalent biochemical properties since their divergence early in vertebrate evolution.
Project description:SIX2 is expressed by the self-renewing nephron progenitors in the human fetal kidney. We have also discovered that SIX1 is expressed in nephron progenitor population of the human fetal kidney, which is in contrast to the mouse. We performed ChIP-seq of SIX1 and SIX2 in order to identify the target genes of each factor and compare the role that each factor plays in transcriptional regulation of the nephron progenitors. We additionally performed ChIP-seq for p300 and H3K27ac in order to identify active loci and complement the transcription factor data.
Project description: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.
Project description: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.
Project description:By obtaining over four billion bases of sequence from chromatin immunoprecipitated DNA in MCF-7 cells with six2 overexpression or not, we generated genome-wide chromatin-state maps of these two cells. We identified the detailed binding sites of six2 in MCF-7 cells.
Project description:Self-renewing undifferentiated nephron progenitors express Six2, a transcription factor that is required for their maintenance as undifferentiated progenitors. Differentiation of nephron progenitors is triggered by Wnt/b-catenin signaling. In order to understand how Six2 and Wnt signaling counteract each other, we performed ChIP-seq of Six2 and b-catenin in mesenchymal nephron progenitor cells. Nephron progenitors were FACS-isolated from BAC transgenic Six2GFPcre-positive embryonic kidneys at E16.5. For Six2 ChIP, freshly FACS isolated Six2+ cells were used. For b-catenin ChIP, FACS isolated Six2+ cells were aggregated by centrifugation at 850g for 5min and incubated in 10%FBS/DMEM containing 4uM BIO for 24hrs.
Project description:Six1 is a critical transcription factor for specifying cell fates in multiple organs and shares common DNA-binding sites with Six2/4/5. However, its molecular function in defining the specificity of Six1-DNA interactions and in instructing cell fates is poorly understood. We performed Six1 ChIP-seq analyses in E10.5 mouse embryos and E13.5 cochleae to map genome-wide CRMs through which Six1 and its interacting TFs function in a combinatorial fashion to control the network of gene regulation necessary for proper development. Genome-wide characterization has identified a robust set of Six1 targets in embryos and auditory sensory epithelium, including genes participating in Wnt/Notch/Shh/Fgf signaling pathways and regulators critical for auditory hair cell formation. Our data provide insights into how Six1 acts in multiple regulatory networks operating in distinct cell types at different stages.
Project description:To identify novel transcriptional targets following Qpc inactivation. We deleteted Qpc in SIX2 nephron progenitor cells using a Six2-eGFP/cre BAC transgene. We compared SIX2-expressing progenitors from Six2-Qpc-/- kidneys with control (Six2-Qpc+/-) embryonic kidneys at E18.5.
Project description:In developing mammalian kidney, nephron progenitor cells (NPC) give rise to all cells in mature nephrons. Expression of the transcription factor Six2 marks NPC in developing mouse kidneys. Within the Six2+ cell population, uncommitted NPC is marked by Cited1 expression. Towards the depletion of NPC in P2, most of the Cited1+ NPC is committed. Therefore, most of the Six2+ cells in kidney represents committed NPC. In order to explore the mechanism of NPC self-renewal and differentiation, hereby we generated transcriptionl profiles of uncommitted NPC (Cited1RFP+ cells from kidneys of E16.5 Cited1tagRFP transgenic mice) and committed NPC (Six2GFP+ cells from kidneys of P2 Six2TGC transgenic mice).
Project description:Purpose: The goal of this study is to compare the differential expression of transcripts in control kidneys compared to kidneys lacking the miR-17~92 cluster in nephron progenitors and their derivatives by RNA-seq to identify potential miRNA targets in the mutant kidneys. mRNA profiles of control and mutant (=Six2-TGC; miR-17~92 flx/flx) embryonic day 16 kidneys were generated by deep sequencing, in triplicate, using Illumina HiSeq2000