Abstract 072: Distinct And Evolving Chromatin States And Transcription Factors Determine The Development Of The Kidney Vasculature

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Differentiation of cells that compose the kidney arterioles is crucial for the formation of a functioning kidney. A group of stromal cells expressing the Forkhead Box D1 ( FoxD1 ) transcription factor (TF) will give rise to the metanephric progenitors for the mural cells of the kidneys arteries and arterioles. We investigated the molecular mechanisms that instruct the FoxD1 progenitors to adopt different cell fates to properly assemble the developing kidney vasculature. We generated FoxD1GC;R26R mT/mG mice, where all the FoxD1 descendant’s cells are labeled with green fluorescent protein (GFP). GFP+ cells were isolated by FACS from kidney cortices and performed either single-cell RNA-Seq (scRNA-Seq) or single-cell Assay for Transposase-Accessible Chromatin (scATAC-Seq ) at different developmental ages: embryos (E12 and E18) and post-natal (P5 and P30) . The integrative analysis of scRNA-Seq and scATAC-Seq identified the FoxD1 derivative cell populations and their respective accessible chromatin areas over the developmental pathway. Motif analysis revealed the binding sites to putative TFs repertoire for each of the FoxD1 descendants. Therefore, we generated differentiation trajectories to track the transcriptome and epigenetics changes that occur along the differentiation pathway. At E12, the FoxD1 progenitor cells harbor open chromatin to bind TFs such as Zeb1, Maz, Snai2 and Pbx1 (p_adjusted_value (padj).: 6.7E-40; 3.6E-40; 4.1E-28; 2.5E-5; respectively) . The gene expression levels of these TFs were also significant (padj.: 5.7E-68; 6.2E-53; 4.4E-49; 2.6E-47, respectively ) . All these TFs are strongly correlated to embryogenesis. As development progresses, new open chromatin areas emerge within a different transcriptome. Interestingly, from E18 ahead, all the FoxD1 decendants exhibited the Mef2 family of TFs as the highest enriched motifs. At P30, among all the FoxD1 decendants, the Juxtaglomerular Cells have the highest enrichment score for all the Mef2 family members (padj.: 0). Thus, as the cells differentiate they acquire distinct chromatin landscapes and TF repertoires. In addition to these unique landscapes Mef2 family of TFs are prominent for the FoxD1 descendants differentiation and kidney vascular development.