Sampson, W. G. B. | Search bioRxiv

bioRxiv2026

Injury-induced Cxcl11 and neutrophil signaling drive zebrafish kidney regeneration by generating a nephrogenic niche of Fgf and Wnt expression

Adult zebrafish regenerate their kidneys after injury by activating quiescent renal stem cells, however the injury signals that activate kidney stem cells are not known. We show here that an innate immune, cytokine response after tubule injury is required and sufficient to induce adult zebrafish kidney regeneration. An injury reporter zebrafish transgenic, Tg(kim1:mScarlet3), revealed that tubule injury occurred specifically in kidney proximal tubules and was associated with a rapid accumulation of neutrophils and macrophages. Injury also activated a Tg(NFkB:GFP) reporter transgene specifically in kidney tubules where RNA seq revealed NFkB target gene and cytokine expression. Inhibition of NFkB signaling with JSH-23 blocked Tg(NFkB:GFP) reporter activation and also inhibited induction of new nephrons. Systemic injection of the immune activators lipopolysaccharide or zymosan into uninjured fish rapidly induced cytokine expression followed by nephrogenic gene expression and the appearance of new, functional nephrons. Analysis of injury-induced cytokines revealed that several paralogs of cxcl11 were strongly expressed throughout the regeneration response and injection of recombinant Cxcl11 was sufficient to induce FGF-dependent kidney stem cell aggregation, but not Wnt-dependent epithelial differentiation. Kidney injury in zebrafish expressing a neutrophil dominant negative rac2D57N transgene activated Fgf signaling but failed to induce wnt9b or downstream Wnt target genes. Nephrogenic gene expression and epithelial tubule formation was rescued by treatment with the canonical Wnt agonist CHIR. Our findings demonstrate that an injury-induced, sterile immune response regulates kidney regeneration by establishing a nephrogenic niche of Fgf and Wnt signaling that supports tissue-resident kidney stem cell differentiation into functional nephrons.

developmental biology↗

bioRxiv2025

Multiple Wnt signaling pathways direct epithelial tubule interconnection in the regenerating zebrafish kidney

Epithelial tubule fusion is fundamental for kidney morphogenesis. Differentiating nephron tubules interconnect with collecting system epithelia to generate a lumenal pathway for fluid excretion. In the adult zebrafish kidney, nephrogenesis occurs as a regenerative response to injury and provides a model to explore cell signaling pathways required for tubule interconnection. We show that canonical Wnt signaling at the junction between two tubules induces a mesenchymal, invasive cell phenotype and is required, along with Src kinase and rac1, to generate basal cell protrusions. The Wnt ligands wnt9b and wnt4 are both required for new nephron formation after injury. Mutation in wnt4 or treatment with the canonical Wnt inhibitor IWR1 blocks formation of basal protrusions in forming nephrons. Mutation in the Wnt receptor frizzled9b reveals a fusion-associated non-canonical Wnt pathway that acts to 1) restrict canonical Wnt gene expression, 2) drive Rho kinase-dependent apical constriction of epithelial cells, and 3) position basal protrusions and generate orthogonal tubule lumenal connections. As a result, frizzled9b mutant nephrons fail to fully interconnect with target distal tubules. Our results indicate that canonical and non-canonical Wnt signaling interact in the same cells to orient and drive tubule interconnection in the regenerating zebrafish kidney.

developmental biology↗