Tcf21 as a founder transcription factor in specifying Foxd1 cells to the juxtaglomerular cell lineage

Renin is crucial for blood pressure regulation and electrolyte balance, and its expressing cells arise from Forkhead box D1-positive (Foxd1⁺) stromal progenitors. However, factors guiding these progenitors toward renin-secreting cell fate remain unclear. Tcf21, a basic helix-loop-helix (bHLH) transcription factor, is essential in kidney development. Using <i>Foxd1^Cre/+;Tcf21^f/f</i> and <i>Ren1^dCre/+;Tcf21^f/f</i> mouse models, we investigated the role of Tcf21 in the differentiation of Foxd1⁺ progenitor cells into juxtaglomerular (JG) cells. Immunostaining and in situ hybridization demonstrated fewer renin-positive areas and altered renal arterial morphology, including the afferent arteriole, in <i>Foxd1^Cre/+;Tcf21^f/f</i> kidneys compared with controls, indicating Tcf21's critical role in the emergence of renin-expressing cells. However, Tcf21 inactivation in renin-expressing cells (<i>Ren1^dCre/+;Tcf21^f/f</i>) did not recapitulate this phenotype, suggesting Tcf21 is dispensable once renin cell identity is established. Using an integrated analysis of single-cell RNA sequencing (scRNA-seq) and single-cell assay for transposase-accessible chromatin sequencing (scATAC-seq) on GFP⁺ cells (stromal lineage) from E12, E18, P5, and P30 <i>Foxd1^Cre/+;Rosa26^mTmG</i> control kidneys, we analyzed the temporal dynamics of Tcf21 expression in cells comprising the JG lineage (<i>n</i> = 2,054). A pseudotime trajectory analysis revealed that Tcf21 expression is highest in metanephric mesenchyme and stromal cells at early developmental stages (E12), with a decline in expression as cells mature into renin-expressing JG cells. Motif enrichment analyses supported Tcf21's significant involvement in early kidney development. These findings underscore the critical role of Tcf21 in Foxd1⁺ cell differentiation into JG cells during early stages of kidney development, offering insights into the molecular mechanisms governing JG cell differentiation and highlighting Tcf21's pivotal role in kidney development.<b>NEW & NOTEWORTHY</b> This manuscript provides novel insights into the role of Tcf21 in the differentiation of Foxd1⁺ cells into JG cells. Using integrated scRNA-seq and scATAC-seq, the study reveals that Tcf21 expression is crucial during early embryonic stages, with its peak at <i>embryonic day 12.</i> The findings demonstrate that inactivation of Tcf21 leads to fewer renin-positive areas and altered renal arterial morphology, underscoring the importance of Tcf21 in the specification of renin-expressing JG cells and kidney development.