Biology subjects

Viola, J. M.

Publications and source records attributed to Viola, J. M..

6 recordsLinked to original sources

bioRxiv2023

Nephron progenitors rhythmically alternate between renewal and differentiation in synchrony with kidney branching morphogenesis

The developing mammalian kidney exponentially duplicates nephron-forming stem cell niches at the tips of the urinary collecting duct tree to achieve massively parallel function. Nephron formation rate has a clinically meaningful effect on person-to-person variability in nephron endowment1-5, while exerting in vitro control could enable sustained waves of nephrogenesis in organoid-derived synthetic kidney tissues6,7. However, how the kidney arrives at an appropriate number and ratio of nephrons to collecting ducts is unclear. Here we show that nephron formation is rhythmic and synchronized with branching of the ureteric bud tree (the future urinary collecting ducts). We correlate human and mouse spatial transcriptomics data with the branching life-cycle to uncover rhythmically alternating signatures of nephron progenitor differentiation and renewal. The nephron progenitor rhythm parallels rhythmic nuclear elongation and other hallmarks of mechanical tension in surrounding stromal cells that we attribute to branching-induced deformation. Stroma-specific knockdown of actomyosin activity leads to a striking loss of synchronization between nephron formation and ureteric bud branching without blocking either. These results suggest that the stroma acts as a mechanically entrained pacemaker for nephron formation. Together, our findings uncover a feedback mechanism for clock-like coordination of organ composition during exponential growth.

developmental biology↗

bioRxiv2023

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

Controlling the time and place of nephron formation in vitro would improve nephron density and connectivity in next-generation kidney replacement tissues. Recent developments in kidney organoid technology have paved the way to achieving self-sustaining nephrogenic niches in vitro. The physical and geometric structure of the niche are key control parameters in tissue engineering approaches. However, their relationship to nephron differentiation is unclear. Here we investigate the relationship between niche geometry, cell compartment mixing, and nephron differentiation by targeting the Rho/ROCK pathway, a master regulator of the actin cytoskeleton. We find that the ROCK inhibitor Y-27632 increases mixing between nephron progenitor and stromal compartments in native mouse embryonic kidney niches, and also increases nephrogenesis. Similar increases are also seen in reductionist mouse primary cell and human induced pluripotent stem cell (iPSC)-derived organoids perturbed by Y-27632, dependent on the presence of stromal cells. Our data indicate that niche organization is a determinant of nephron formation rate, bringing renewed focus to the spatial context of cell-cell interactions in kidney tissue engineering efforts.

bioengineering↗

bioRxiv2022

Independent control over cell patterning and adhesion on hydrogel substrates for tissue interface mechanobiology

Replicating organizational principles that establish fine-scale tissue structure is critical to our capacity for building functional replacement tissues. Tissue boundaries such as epithelial-mesenchymal interfaces are engines for morphogenesis in vivo. However, despite a wealth of micropatterning approaches available to control tissue size, shape, and mechanical environment in vitro, fine-scale spatial control of cell composition within tissue constructs remains an engineering challenge. To address this, we augment DNA "velcro" technology for selective patterning of ssDNA-labeled cells with long-term culture on mechanically defined polyacrylamide hydrogels. We co-functionalize photoactive benzophenone-containing polyacrylamide gels (BP-PA gels) with spatially precise ssDNA features that confer temporary cell adhesion and with extracellular matrix (ECM) proteins that confer long-term adhesion. We find that co-functionalization does not compromise ssDNA patterning fidelity or cell capture, nor hydrogel mechanical properties or mechanosensitive fibroblast spreading, enabling mechanobiology studies of precise cell interfaces. We then co-pattern colonies of fibroblasts and epithelial cells to study interface formation and extracellular signal-related kinase (ERK) activity at cellular contacts. Combining DNA velcro and ECM functionalization approaches provides independent control of initial cell placement, adhesion, and mechanical environment, constituting a new tool for studying biological interfaces and for programming multicellular interactions in engineered tissues.

bioengineering↗

bioRxiv2022

Tubule jamming in the developing kidney creates cyclical mechanical stresses instructive to nephron formation

The kidney develops through branching of progressively crowded ureteric bud (UB) tubules at the organ surface. The elongating tubule tips are surrounded by traveling cap mesenchyme niches consisting of nephron progenitors and separated by stromal boundaries. Dynamic interactions between these tissues coordinate a balance between UB tip branching, elongation, and nephron induction that sets nephron numbers for life, impacting the likelihood of adult disease. Such a crowded tissue environment could place geometric limits on the number of niches that can be formed while maintaining mechanical integrity of the tissue. Since space is at a premium, crowding could also force a given niche to prioritize between nephron formation or UB branching differently depending on its spatial context. Here we study the geometric and mechanical consequences of tubule tip crowding at the embryonic kidney surface. Organ curvature reduces and tubule tip domain niches 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. To infer mechanical dynamics over the branching timescale, we define a new method to infer tip domain ages relative to their most recent branch events from fixed kidneys. We find that new tip domains overcome mechanical resistance as they branch and displace close-packed neighbors, transiently increasing mechanical stress in the niche. Ongoing efforts to understand geometric and mechanical effects on niche regulation will clarify variation in kidney tissue composition and advance engineering control strategies for synthetic regenerative tissues.

bioengineering↗

bioRxiv2021

The developing kidney actively negotiates geometric packing conflicts to avoid defects

The physiological functions of several organs rely on branched tubular networks, but little is known about conflicts in development between building enough tubules for adequate function and geometric constraints imposed by organ size. We show that the mouse embryonic kidney epithelium negotiates a physical packing conflict between tubule tip duplication and limited area at the organ surface. Imaging, computational, and soft material modeling of tubule families identifies six geometric packing phases, including two defective ones. Experiments in kidney explants show that a retrograde tension on tubule families is necessary and sufficient for them to avoid defects by switching to a vertical orientation that increases packing density. These results reveal developmental contingencies in response to physical limitations, and create a framework for classifying kidney defects. One-Sentence SummaryEpithelial branching in the kidney causes a geometric packing conflict that is resolved through internally generated tensions

developmental biology↗

bioRxiv2019

Kinomorphs: Shape-shifting tissues for developmental engineering

Current methods for building tissues usually start with a non-biological blueprint, or rely on self-organization, which does not extend to organ-scales. This has limited the construction of large tissues that simultaneously encode fine-scale cell organization. Here we bridge scales by mimicking developmental dynamics using \"kinomorphs\", tissue scaffolds that undergo globally programmed shape and density changes to trigger local self-organization of cells in many locations at once. In this first report, we focus on mimicking the extracellular matrix (ECM) compaction and division into leaflets that occurs in kidney collecting duct development. We start by creating single-cell resolution cell patterns in ECM-mimetic hydrogels that are >10x larger than previously described, by leveraging photo-lithographic technology. These patterns are designed to mimic the branch geometry of the embryonic kidney collecting duct tree. We then predict the shape dynamics of kinomorphs driven by cell contractility-based compaction of the ECM using kinematic origami simulations. We show that these dynamics spur centimeter-scale assembly of structurally mature ~50 m-diameter epithelial tubules that are locally self-organized, but globally programmed. Our approach prescribes tubule network geometry at ~5x smaller length-scales than currently possible using 3D printing, and at local cell densities comparable to in vivo tissues. Kinomorphs could be used to scaffold and \"plumb\" arrays of organoids in the future, by guiding the morphogenesis of epithelial networks. Such hybrid globally programmed/locally self-organized tissues address a major gap in our ability to recapitulate organ-scale tissue structure.\n\nSignificance StatementEngineers are attempting to build tissues that mimic human diseases outside of the body. Although stem cells can be coaxed to form small organoids with a diversity of cell types, they do not properly organize over large distances by themselves. We report a strategy to mimic developmental processes using dynamic materials that attempt to guide a cellular \"blueprint\" towards a more complex tissue endpoint. We call these materials kinomorphs, combining the Greek kino (propel, drive) and morfi (form, shape), since they seek to shepherd both the shape and developmental trajectory of cell collectives within them. Kinomorphs could pave the way towards organ-scale synthetic tissues built through a hybrid of engineering and self-organization strategies.

bioengineering↗