Hmx2 and Dmrt2 Coordinate the Differentiation of Intercalated Cell Subtypes in Kidney

Key Points Hmx2 was required for type B intercalated cell differentiation but became dispensable in the absence of Dmrt2. Dmrt2 promoted type A differentiation of intercalated cells and repressed type B identity. Early divergence of Dmrt2 and Hmx2 marked subtype specification of intercalated cells. Background Intercalated cells in the kidney collecting ducts are essential for maintaining systemic acid–base homeostasis. Based on gene expression profiles and functional characteristics, intercalated cells are classified into type A, type B, non-A/non-B. Although several transcription factors have been reported to regulate intercalated cell differentiation, how the fates of intercalated cell subtypes are established remains unclear. Methods To investigate the roles of Dmrt2 and Hmx2 in intercalated cell subtype differentiation, we generated mice with single or double conditional deletion and knock-in of these transcription factors specifically in distal nephron segments and analyzed their effects on urine acidification. We also performed single-cell RNA sequencing analysis on mouse and human kidney datasets to trace intercalated cell progenitor fate trajectories. Results Loss of Hmx2 in the distal nephron prevented type B intercalated cell differentiation, whereas simultaneous deletion of Hmx2 and Dmrt2 compromised type A intercalated cell differentiation, with a concomitant increase in Hmx3 expression and type B intercalated cell differentiation. Dmrt2 knock-in mice exhibited a modest increase in type A intercalated cell differentiation and a marked reduction in type B intercalated cells. Notably, Dmrt2 knock-in did not rescue the intercalated cell differentiation defects observed in Foxp1-deficient mice. Analysis of mouse and human single-cell RNA sequencing data further confirmed the mutually exclusive expression patterns of Hmx2 and Dmrt2 in the kidney. Conclusions Hmx2 and Dmrt2 were essential, mutually exclusive transcription factors that govern intercalated cell subtype differentiation in the kidney, with Hmx2 specifying type B intercalated cell fate and Dmrt2 promoting type A intercalated cell differentiation. Dmrt2 suppressed the expression of Hmx2 and Hmx3. In the absence of Dmrt2 and Hmx2, Hmx3 expression was activated to promote type B intercalated cell differentiation.