Tubule jamming in the developing mouse kidney creates cyclical mechanical stresses in nephron-forming niches

Abstract

The kidney develops through elaboration of ureteric epithelial tubules (the future urinary collecting ducts), stroma, and nephron progenitors in the cap mesenchyme that surrounds each ureteric tip as they branch. Dynamic interactions between these tissues coordinate a balance between ureteric tip branching and nephron formation that sets nephron numbers for life, which impacts the probability of adult disease. How then is this balance achieved? Here we study the geometric and mechanical consequences of tubule tip crowding at the embryonic kidney surface and its effect on nephron formation. We find that kidney surface curvature reduces and tubule 'tip domains' pack more closely over developmental time. These together create a semi-crystalline geometry of tips at the kidney surface and a rigidity transition to more solid-like tissue properties at later developmental stages. New tips overcome mechanical resistance as they branch, expand, and displace close-packed neighbors, after which residual mechanical stress dissipates. This correlates with a changing nephrogenesis rate over the tip 'life-cycle'. To draw a causal link between the two, we mimic a mechanical transient in human iPSC-derived nephron progenitor organoids and find increased cell commitment to early nephron aggregates. The data suggest that temporal waves of mechanical stress within nephron progenitor populations could constitute a clock that synchronizes nephron formation and ureteric tubule duplication after E15. Ongoing efforts to understand the spatial and temporal regulation of nephron induction will clarify variation in nephron endowment between kidneys and advance engineered kidney tissues for regenerative medicine.

Nephron progenitors rhythmically alternate between renewal and differentiation phases that synchronize with kidney branching morphogenesis

“…We validated several hits at the protein level, especially downstream of Wnt signaling, that are crucial to nephron progenitor commitment to early nephron stages. The data provide molecular-level insight into our previous inference that nephrogenesis pauses early in each branching cycle 29 . We also show that incorporation of rhythmic signaling in human iPSC-derived nephron progenitor organoids may aid synthetic control over renewal vs. differentiation decision-making in contexts removed from native branching morphogenesis, essential to the development of organoids and tissue chips for kidney regenerative medicine.…”

“…However, the relative rates of renewal vs differentiation may not be constant in time, since cells commit as transient avalanche-like streams from the cap mesenchyme into discrete PTAs 28 . Indeed, we recently reported that nephron formation rate is not constant over the ureteric bud branching cycle, but rather nephron formation pauses after each branch event and resumes before the next one 29 . These observations suggest both a switch-like response of progenitors to inductive cues as single cells and an avalanche-like response to inductive cues as cell collectives.…”

Rho/ROCK activity tunes cell compartment segregation and differentiation in nephron-forming niches

“…5C ). Interestingly, Y-27632 treated spheroids had similar rebound velocities (inferred tension) as nephron-forming niches in the E17 mouse kidney cortex (Viola et al 2023). Organoids were analyzed immediately after the 48 hr treatment to catch early differentiation events by immunofluorescence for SIX2 and the early nephron marker LHX1 ( Fig.…”

“…Stromal cells migrate and split the existing cap mesenchyme compartment in two during ureteric bud tip bifurcations (Munro, Hohenstein, and Davies 2017), and nephron progenitors occasionally cross stromal boundaries (Combes et al 2016). Our recent work has noted variation in cap mesenchyme-stromal compartment mechanical stress (Viola et al 2023) and mixing over the branching morphogenesis ‘life-cycle’ (Hughes Lab, in preparation ). Y-27632 is potentially mimicking several of these processes here.…”

Measurement of adhesion and traction of cells at high yield (MATCHY) reveals an energetic ratchet driving nephron condensation

“…Second, removing cells from their native tissue environment risks distorting readout of true in vivo biophysical properties by altering surface adhesion receptor integrity and limiting measurements to those possible through cell interactions with an appropriate traction force substrate or single partner cell type in adhesion measurements. For many questions, these caveats are likely to be a reasonable tradeoff against the volume of information that can be gathered by MATCHY compared to the few in vivo measurement tools that exist (37,(93)(94)(95)(96)(97)(98)(99).…”