The thin descending limb of the loop of Henle originates from proximal tubule cells during mouse kidney development.

Background: The thin descending limb (DTL) of the loop of Henle is crucial for urine concentration, as it facilitates passive water reabsorption. Despite its importance, little is known about how DTL cells form during kidney development. Single-cell RNA sequencing (scRNA-seq) studies have not definitively identified DTL cells in the developing mouse kidney.

Methods: We assembled a large scRNA-seq dataset by integrating multiple datasets of non-mutant developing mouse kidneys to identify developing DTL cells. To test whether DTL cells originate from proximal tubule (PT) cells, we generated a PT-specific Cre line, , and conducted lineage tracing of PT cells. Additionally, given that the transcription factor Hnf4a directly binds to the gene, we examined whether the loss of Hnf4a affects expression in DTL cells.

Results: From our scRNA-seq dataset, we identified a small cluster of cells distinct from both the proximal tubule and the thick ascending limb of the loop of Henle. Those cells exhibited high expression of DTL marker genes, including and . Notably, a subset of PT cells also expressed DTL marker genes, suggesting that PT cells may give rise to DTL cells. Using lineage tracing with the line, we found that DTL cells were positive for the Rosa26 reporter, confirming that DTL cells are descendants of PT cells. Furthermore, the loss of Hnf4a, a transcription factor essential for mature PT cell formation, disrupted proper expression in DTL cells, providing additional evidence of a developmental link between PT cells and DTL cells.

Conclusion: Our findings shed new light on the developmental origin of DTL cells and highlight the importance of Hnf4a in regulating their formation.

Key Points: Reference single cell RNA-seq dataset of the developing mouse kidney was assembled and used to identify the thin descending limb of the loop of Henle.Lineage analysis of proximal tubules in the mouse kidney shows that proximal tubule cells give rise to the thin descending limb of the loop of Henle. Deletion of Hnf4a disrupts the expression of in the thin descending limb of the loop of Henle, highlighting a developmental link between proximal tubules and the loop of Henle.