No Differences in Clinical, Functional, or Patient-Reported Outcomes Following Trial of Nonoperative Management Before Open Reduction and Internal Fixation of Humeral Shaft Fractures.

OBJECTIVES: To test the hypothesis that primary osteosynthesis of humeral shaft fractures may lead to more favorable clinical, functional, and patient-reported outcomes than fixation following a trial of nonoperative management. DESIGN: Retrospective cohort review. SETTING: Academic level I trauma center. PATIENT SELECTION CRITERIA: Adult patients who presented with humeral shaft fractures and ultimately underwent open reduction and internal fixation (ORIF) from May 2011 to May 2021. Patients who underwent ORIF within 2 weeks of injury were grouped into the primary osteosynthesis cohort, and patients who underwent ORIF >4 weeks from the date of injury were grouped into the trial of nonoperative cohort. OUTCOME MEASURES AND COMPARISONS: Postoperative complications, elbow arc of motion, time to radiographic union, and patient-reported outcomes were investigated and compared between the primary osteosynthesis and trial of nonoperative management cohorts. RESULTS: One hundred twenty-seven patients fit the study criteria, 84 underwent primary osteosynthesis and 43 trialed initial nonoperative treatment. No differences were found in patient demographics between the primary osteosynthesis and trial of nonoperative management cohorts, including age (53 ± 19 vs. 57 ± 18; P = 0.25), sex (39% vs. 44% male, 61% vs. 56% female; P = 0.70), and Body Mass Index (BMI) (30 ± 6 vs. 32 ± 9; P = 0.38). The average time to operative intervention in the primary osteosynthesis group was 4 days (0-14 days) and 105 days (28-332 days) in the trial of nonoperative treatment group ( P < 0.01). No differences were found with regard to intraoperative blood loss, total operative time, time to radiographic union (determined using the Radiographic Union Scores for Humeral scoring system), or overall complication rates, including primary and secondary radial nerve injuries ( P = 0.23 and 0.86, respectively). Patients reported similar patient-reported outcomes measurement information system pain interference ( P = 0.73), depression (D) ( P = 0.99), and physical function ( P = 0.66) scores at their 6-month postsurgical follow-up visits. CONCLUSIONS: Patients who attempted a trial of nonoperative management for humeral shaft fractures before ORIF had similar clinical, functional, and patient-reported outcomes as those who underwent primary osteosynthesis. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Adjunctive dorsal spanning plate fixation for challenging distal radius injuries.

Background: Distal radius fractures with severely osteoporotic bone or articular comminution can provide challenges to fixation with traditional volar locked plating alone. The purpose of this study was to evaluate the clinical, radiographic, and patient reported outcomes of patients undergoing distal radius fixation with volar locked plating and adjunctive dorsal bridge plating. Methods: We retrospectively identified 16 patients with distal radius fractures who underwent our preferred surgical technique for fixation. Patients underwent volar locked plate fixation as well as dorsal bridge fixation at time of surgery. Seven patients were indicated for severe articular comminution with volar rim fragmentation (44%), three patients were revised for nonunion after previous volar locked late fixation (19%), and six patients had severely osteoporotic bone with articular comminution (38%). Two patients (13%) sustained AO/OTA 23-A3 distal radius fracture, two patients (13%) had a 23-B3 fracture, two patients (13%) had a 23-C2 fracture and ten patients (63%) had a 23-C3 fracture. Results: The average patient age was 51.8 years ± 20.6. Patients were followed for an average of 12.2±6.3 months. The dorsal bridge plate was removed at an average of 11.1±2.4 weeks. The average post-operative radial inclination was 18.9±2.4°, radial height 12.4 mm ± 2.6 mm, and volar tilt 7.1±1.9°. There were no cases of deep or superficial infection. After dorsal bridge plate removal, patients demonstrated an average wrist extension of 55.3±9.5°, flexion 54.4±12.8°, radial deviation 15.7±3.2°, 25.2±3.9 degrees of ulnar deviation. Conclusion: Distal radius fractures in the setting of severely osteoporotic bone, salvage procedures, articular comminution, volar rim fractures, and revision surgery present uniquely difficult surgical challenges. Volar locked plating with adjunctive dorsal bridge plating can be used with good short- and long-term results.

Comparative genomics incorporating translocation renal cell carcinoma mouse model reveals molecular mechanisms of tumorigenesis.

Translocation renal cell carcinoma (tRCC) most commonly involves an ASPSCR1-TFE3 fusion, but molecular mechanisms remain elusive and animal models are lacking. Here, we show that human ASPSCR1-TFE3 driven by Pax8-Cre (a credentialed clear cell RCC driver) disrupted nephrogenesis and glomerular development, causing neonatal death, while the clear cell RCC failed driver, Sglt2-Cre, induced aggressive tRCC (as well as alveolar soft part sarcoma) with complete penetrance and short latency. However, in both contexts, ASPSCR1-TFE3 led to characteristic morphological cellular changes, loss of epithelial markers, and an epithelial-mesenchymal transition. Electron microscopy of tRCC tumors showed lysosome expansion, and functional studies revealed simultaneous activation of autophagy and mTORC1 pathways. Comparative genomic analyses encompassing an institutional human tRCC cohort (including a hitherto unreported SFPQ-TFEB fusion) and a variety of tumorgraft models (ASPSCR1-TFE3, PRCC-TFE3, SFPQ-TFE3, RBM10-TFE3, and MALAT1-TFEB) disclosed significant convergence in canonical pathways (cell cycle, lysosome, and mTORC1) and less established pathways such as Myc, E2F, and inflammation (IL-6/JAK/STAT3, interferon-γ, TLR signaling, systemic lupus, etc.). Therapeutic trials (adjusted for human drug exposures) showed antitumor activity of cabozantinib. Overall, this study provides insight into MiT/TFE-driven tumorigenesis, including the cell of origin, and characterizes diverse mouse models available for research.

Determination of the Inter- and Intra-rater Reliability of Fusion Assessment in First Tarsometatarsal Joint Arthrodesis Using CT Scan: An Observational Study.

Background: First tarsometatarsal joint arthrodesis is a common procedure performed by podiatrists and orthopedic surgeons. There remains debate on how useful CT scans are in assessing fusion status in the post-operative patient. The purpose of our study was to determine the reliability among both orthopedic surgeons and radiologists in reviewing both postoperative radiographs and CT in order to determine if fusion had occurred in patients undergoing 1st tarsometatarsal arthrodesis. A secondary purpose of this study was to determine if CT offered improved inter- and intra-rater reliability when compared to plain radiographs. Methods: Patients who underwent 1st tarsometatarsal arthrodesis were retrospectively reviewed and those who underwent CT post-operatively for persistent pain were identified. Orthopedic surgeons and radiologists then analyzed the radiographs and CT of these patients for union with a threshold for union being set at 50% of the joint being fused. Imaging was then re-evaluated by the same provider 6 months later. Results: 24 patients were identified meeting inclusion criteria. Inter-rater reliability and intra-rater reliability for assessment of 1st tarsometatarsal arthrodesis were better with CT compared to radiographs; however, this association was not deemed reliable. Both imaging modalities were not able to assess union status confidently and reliably across reviewers, although CT scan had better intra-rater reliability. Conclusions: While CT is frequently used to assess fusion in patients who have underwent 1st tarsometatarsal arthrodesis, it was not found to be better than radiographs. Practitioners should reconsider the use CT as the gold standard when assessing fusion in this population.

An Analysis of Patient-Reported Outcomes Measurement Information System (PROMIS) in Non-operative Posterolateral Elbow Dislocations.

INTRODUCTION: The purpose of our study is to analyze the outcomes of traumatic posterolateral elbow dislocations using patient-reported outcomes measurement information system (PROMIS). We hypothesized that physical function (PF) and upper extremity (UE) scores in PROMIS will significantly improve over six months of follow-up and correlate with a positive change in the patient-acceptable symptom state (PASS). METHODS: This is a seven-year retrospective study of 165 consecutive adult patients with traumatic posterolateral elbow dislocations. Demographic information, PROMIS PF, PROMIS UE, PROMIS pain interference (PI), PROMIS depression, and PASS were recorded over six months of follow-up. RESULTS: At the time of injury, mean PROMIS scores were PF 41.24 (SD 11.16), UE 34.27 (SD 11.87), PI 60.44 (SD 8.07), and depression 49.82 (SD 10.42). At six months, the mean PROMIS scores were PF 39.71 (SD 9.71), UE 33.95 (SD 9.09), PI 57.35 (SD 8.59), and depression 51.43 (SD 10.62). The overall six-month changes in PROMIS scores were PF -1.53, UE -0.32, PI -3.09, and depression +1.61. At the 6-month follow-up, 41.7% responded positively on the PASS, which correlated only with PROMIS PI. CONCLUSIONS: Among patients who improved from negative to positive response on PASS, the PROMIS PF, UE, and depression scores did not significantly improve. Only PROMIS PI correlated with PASS at the six-month follow-up; PROMIS PI significantly improved among simple posterolateral elbow dislocation patients at both short-term and long-term follow-up points. PROMIS PF, UE, and depression did not significantly differ between time of injury and short-term and long-term follow-up points.

Non-operative Treatment of Mason Type I Radial Head Fractures: A Comparative Analysis Using Patient-Reported Outcomes Measurement Information System (PROMIS).

OBJECTIVES: The purpose of this study is to compare the outcomes of Mason type I radial head fractures. This information will help to provide physicians with a critical decision-making tool when considering non-operative intervention and evaluate Patient-Reported Outcomes Measurement Information System (PROMIS) as a potentially valuable measure to track outcomes. METHODS: We retrospectively identified 527 patients undergoing non-operative intervention. Demographic information, physical exam measurements, patient acceptable symptom state (PASS), and PROMIS Upper Extremity (UE), Physical Function (PF), and Pain Interference (PI) scores were analyzed over 12 months. RESULTS: At the initial outpatient post-injury visit (within one week of injury), the average PROMIS PF, UE, PI, and Depression were 42.04 (SD: 6.3), 35.31 (SD: 7.3), 59.18 (SD: 9.2), and 48.68 (SD: 6.8), respectively. The average change in PROMIS PF, UE, PI, and Depression scores from the time of injury to six weeks were -0.23 (p=0.7), 1.43 (p=0.03), -2.1 (p=0.01), and -0.99 (p=0.1). The average change in PROMIS PF, UE, PI, and Depression scores from the time of injury to six months was -0.56 (p=0.56), 1.84 (p<0.001), -1.84 (p<0.001), and -0.13 (p=0.68). Among patients initially reporting "not acceptable" on PASS and reporting "acceptable" at the six-month visit, the average PROMIS PF, UE, PI, and Depression scores were 42.14, 38.91, 56.91, and 47.51 respectively. This represents an average difference of 1.11 (p=0.07), 2.82 (p<0.01), -1.19 (p=0.04), and -1.7 (p=0.01) respectively. CONCLUSION: PROMIS UE and PI significantly improved among Mason I radial head fractures treated non-operatively at both six-week and six-month follow-up points but did not meet the mean clinically important difference (MCID) PROMIS PF did not significantly differ between the time of injury, six-week or six-month follow-up points. Only PROMIS UE correlated with PASS at six-week and six-month follow-up. Among patients who improved from negative to positive responses on PASS, PROMIS UE, and PI significantly improved.

Genetically engineering endothelial niche in human kidney organoids enables multilineage maturation, vascularization and de novo cell types.

Vascularization plays a critical role in organ maturation and cell type development. Drug discovery, organ mimicry, and ultimately transplantation in a clinical setting thereby hinges on achieving robust vascularization of in vitro engineered organs. Here, focusing on human kidney organoids, we overcome this hurdle by combining an inducible ETS translocation variant 2 (ETV2) human induced pluripotent stem cell (iPSC) line, which directs endothelial fate, with a non-transgenic iPSC line in suspension organoid culture. The resulting human kidney organoids show extensive vascularization by endothelial cells with an identity most closely related to endogenous kidney endothelia. Vascularized organoids also show increased maturation of nephron structures including more mature podocytes with improved marker expression, foot process interdigitation, an associated fenestrated endothelium, and the presence of renin+ cells. The creation of an engineered vascular niche capable of improving kidney organoid maturation and cell type complexity is a significant step forward in the path to clinical translation. Furthermore, this approach is orthogonal to native tissue differentiation paths, hence readily adaptable to other organoid systems and thus has the potential for a broad impact on basic and translational organoid studies.

Endoscopic Versus Open Carpal Tunnel Surgery: Risk Factors and Rates of Revision Surgery.

PURPOSE: The purpose of our study was to compare the 1-year revision surgery rates and outcomes of open versus endoscopic carpal tunnel release. Our hypothesis was that, compared to open release, endoscopic carpal tunnel release was an independent risk factor for revision surgery within 1-year. METHODS: This was a retrospective cohort study of 4338 patients undergoing isolated endoscopic or open carpal tunnel release. Demographic data, medical comorbidities, surgical approach, need for revision surgery, hand dominance, history of prior injection, and Patient Reported Outcomes Measurement Information System upper extremity (UE), pain interference (PI) and physical function scores were analyzed. Multivariable analysis was used to identify the risk factors for revision surgery within one year of the index procedure. RESULTS: In total, 3280 patients (76%) underwent open and 1058 (24%) underwent endoscopic carpal tunnel release. Within one year of the index procedure, 45 patients required revision carpal tunnel release. The average time to revision was 143 days. The rate of revision carpal tunnel release in the open group was 0.71% compared to 2.08% in the endoscopic group. Multivariable analysis demonstrated that endoscopic surgery, male sex, cubital tunnel syndrome, tobacco use, and diabetes were associated independently with revision surgery. CONCLUSIONS: In this study, we found that endoscopic carpal tunnel release was associated independently with a 2.96 times greater likelihood of requiring revision carpal tunnel release within one year, compared to open carpal tunnel release. Male sex, concurrent cubital tunnel syndrome, tobacco use, and diabetes also were associated independently with greater risk of needing revision carpal tunnel release within one year. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognostic II.

Eponyms Describing Soft Tissue Pathologies in Orthopedic Hand Surgery.

Orthopedic surgery literature utilizes numerous eponyms, and they have become commonplace among orthopedic surgeons and the general public alike. These eponyms can have important historical implications and their history is often overlooked by the physicians using such terms. This paper seeks to specifically explore the origins of eponyms in orthopedic soft tissue diseases involving the upper extremity. Shedding light onto the origin of these eponyms can provide greater respect and understanding of their use in orthopedic surgery today.

Isolated Avulsion Fracture of the Extensor Carpi Ulnaris: A Case Report and Review of Literature.

Avulsion fractures of the extensor carpi ulnaris (ECU) insertion are rare injuries that are poorly described in the literature. Several case reports detail closed ECU ruptures, however, only one previous case report describes an ECU avulsion fracture from the insertion on the fifth metacarpal base in the setting of multiple wrist and hand injuries. To our knowledge, we present the only case report of an isolated ECU avulsion fracture. In our case, a 35-year-old female presented with ulnar-sided wrist pain after forcefully impacting a steering wheel while radially deviating her wrist. She was diagnosed with an ECU avulsion fracture and elected to undergo open repair with a suture button technique. The patient recovered to nearly full strength and range of motion compared to her contralateral side by her eight-week visit. She returned back to work without restrictions after completing hand therapy.

Transcription Factors YAP/TAZ and SRF Cooperate To Specify Renal Myofibroblasts in the Developing Mouse Kidney.

BACKGROUND: The embryonic renal stroma consists of multiple molecularly distinct cell subpopulations, the functional significance of which is largely unknown. Previous work has demonstrated that the transcription factors YAP and TAZ play roles in the development and morphogenesis of the nephrons, collecting ducts, and nephron progenitor cells. METHODS: In embryonic mouse kidneys, we identified a subpopulation of stromal cells with enriched activity in YAP and TAZ. To evaluate the function of these cell types, we genetically ablated both Yap and Taz from the stromal progenitor population and examined how gene activity and development of YAP/TAZ mutant kidneys are affected over a developmental time course. RESULTS: We found that YAP and TAZ are active in a subset of renal interstitium and that stromal-specific coablation of YAP/TAZ disrupts cortical fibroblast, pericyte, and myofibroblast development, with secondary effects on peritubular capillary differentiation. We also demonstrated that the transcription factor SRF cooperates with YAP/TAZ to drive expression of at least a subset of renal myofibroblast target genes and to specify myofibroblasts but not cortical fibroblasts or pericytes. CONCLUSIONS: These findings reveal a critical role for YAP/TAZ in specific embryonic stromal cells and suggest that interaction with cofactors, such as SRF, influence the expression of cell type-specific target genes, thus driving stromal heterogeneity. Further, this work reveals functional roles for renal stroma heterogeneity in creating unique microenvironments that influence the differentiation and maintenance of the renal parenchyma.

Integration of Multiple, Diverse Methods to Identify Biologically Significant Marker Genes.

Identification of genes that reliably mark distinct cell types is key to leveraging single-cell RNA sequencing to better understand organismal biology. Such genes are usually chosen by measurement of differential expression between groups of cells and selecting those with the greatest magnitude or most statistically significant change. Many methods have been developed for performing such analyses, but no single, best method has emerged. Validating the results of these analyses is costly in terms of time, effort and resources. We demonstrate that applying an ensemble of such methods robustly identifies genes that mark cells that cluster together and that show restricted expression assessed by antisense mRNA in situ and immunofluorescence. This technique is easily extensible to any number of differential expression methods and the inclusion of additional methods is expected to result in further improvement in performance.

Vascular deficiencies in renal organoids and ex vivo kidney organogenesis.

Chronic kidney disease (CKD) and end stage renal disease (ESRD) are increasingly frequent and devastating conditions that have driven a surge in the need for kidney transplantation. A stark shortage of organs has fueled interest in generating viable replacement tissues ex vivo for transplantation. One promising approach has been self-organizing organoids, which mimic developmental processes and yield multicellular, organ-specific tissues. However, a recognized roadblock to this approach is that many organoid cell types fail to acquire full maturity and function. Here, we comprehensively assess the vasculature in two distinct kidney organoid models as well as in explanted embryonic kidneys. Using a variety of methods, we show that while organoids can develop a wide range of kidney cell types, as previously shown, endothelial cells (ECs) initially arise but then rapidly regress over time in culture. Vasculature of cultured embryonic kidneys exhibit similar regression. By contrast, engraftment of kidney organoids under the kidney capsule results in the formation of a stable, perfused vasculature that integrates into the organoid. This work demonstrates that kidney organoids offer a promising model system to define the complexities of vascular-nephron interactions, but the establishment and maintenance of a vascular network present unique challenges when grown ex vivo.

Schwannoma development is mediated by Hippo pathway dysregulation and modified by RAS/MAPK signaling.

Schwannomas are tumors of the Schwann cells that cause chronic pain, numbness, and potentially life-threatening impairment of vital organs. Despite the identification of causative genes, including NF2 (Merlin), INI1/SMARCB1, and LZTR1, the exact molecular mechanism of schwannoma development is still poorly understood. Several studies have identified Merlin as a key regulator of the Hippo, MAPK, and PI3K signaling pathways; however, definitive evidence demonstrating the importance of these pathways in schwannoma pathogenesis is absent. Here, we provide direct genetic evidence that dysregulation of the Hippo pathway in the Schwann cell lineage causes development of multiple schwannomas in mice. We found that canonical Hippo signaling through the effectors YAP/TAZ is required for schwannomagenesis and that MAPK signaling modifies schwannoma formation. Furthermore, cotargeting YAP/TAZ transcriptional activity and MAPK signaling demonstrated a synergistic therapeutic effect on schwannomas. Our new model provides a tractable platform to dissect the molecular mechanisms underpinning schwannoma formation and the role of combinatorial targeted therapy in schwannoma treatment.

Identification and characterization of cellular heterogeneity within the developing renal interstitium.

Kidney formation requires the coordinated growth of multiple cell types including the collecting ducts, nephrons, vasculature and interstitium. There is a long-held belief that interactions between progenitors of the collecting ducts and nephrons are primarily responsible for kidney development. However, over the last several years, it has become increasingly clear that multiple aspects of kidney development require signaling from the interstitium. How the interstitium orchestrates these various roles is poorly understood. Here, we show that during development the interstitium is a highly heterogeneous patterned population of cells that occupies distinct positions correlated to the adjacent parenchyma. Our analysis indicates that the heterogeneity is not a mere reflection of different stages in a linear developmental trajectory but instead represents several novel differentiated cell states. Further, we find that ß-catenin has a cell autonomous role in the development of a medullary subset of the interstitium and that this non-autonomously affects the development of the adjacent epithelia. These findings suggest the intriguing possibility that the different interstitial subtypes may create microenvironments that play unique roles in development of the adjacent epithelia and endothelia.

Stromal ß-catenin activation impacts nephron progenitor differentiation in the developing kidney and may contribute to Wilms tumor.

Wilms' tumor (WT) morphologically resembles the embryonic kidney, consisting of blastema, epithelial and stromal components, suggesting tumors arise from the dysregulation of normal development. ß-Catenin activation is observed in a significant proportion of WTs; however, much remains to be understood about how it contributes to tumorigenesis. Although activating ß-catenin mutations are observed in both blastema and stromal components of WT, current models assume that activation in the blastemal lineage is causal. Paradoxically, studies performed in mice suggest that activation of ß-catenin in the nephrogenic lineage results in loss of nephron progenitor cell (NPC) renewal, a phenotype opposite to WT. Here, we show that activation of ß-catenin in the stromal lineage non-autonomously prevents the differentiation of NPCs. Comparisons of the transcriptomes of kidneys expressing an activated allele of ß-catenin in the stromal or nephron progenitor cells reveals that human WT more closely resembles the stromal-lineage mutants. These findings suggest that stromal ß-catenin activation results in histological and molecular features of human WT, providing insights into how alterations in the stromal microenvironment may play an active role in tumorigenesis.

Asynchronous mixing of kidney progenitor cells potentiates nephrogenesis in organoids.

A fundamental challenge in emulating kidney tissue formation through directed differentiation of human pluripotent stem cells is that kidney development is iterative, and to reproduce the asynchronous mix of differentiation states found in the fetal kidney we combined cells differentiated at different times in the same organoid. Asynchronous mixing promoted nephrogenesis, and heterochronic organoids were well vascularized when engrafted under the kidney capsule. Micro-CT and injection of a circulating vascular marker demonstrated that engrafted kidney tissue was connected to the systemic circulation by 2 weeks after engraftment. Proximal tubule glucose uptake was confirmed, but despite these promising measures of graft function, overgrowth of stromal cells prevented long-term study. We propose that this is a technical feature of the engraftment procedure rather than a specific shortcoming of the directed differentiation because kidney organoids derived from primary cells and whole embryonic kidneys develop similar stromal overgrowth when engrafted under the kidney capsule.

Time Dependence of Few-Body Förster Interactions among Ultracold Rydberg Atoms.

Rubidium Rydberg atoms in either |m_{j}| sublevel of the 36p_{3/2} state can exchange energy via Stark-tuned Förster resonances, including two-, three-, and four-body dipole-dipole interactions. Three-body interactions of this type were first reported and categorized by Faoro et al. [Nat. Commun. 6, 8173 (2015)NCAOBW2041-172310.1038/ncomms9173] and their Borromean nature was confirmed by Tretyakov et al. [Phys. Rev. Lett. 119, 173402 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.173402]. We report the time dependence of the N-body Förster resonance N×36p_{3/2,|m_{j}|=1/2}→36s_{1/2}+37s_{1/2}+(N-2)×36p_{3/2,|m_{j}|=3/2}, for N=2, 3, and 4, by measuring the fraction of initially excited atoms that end up in the 37s_{1/2} state as a function of time. The essential features of these interactions are captured in an analytical model that includes only the many-body matrix elements and neighboring atom distribution. A more sophisticated simulation reveals the importance of beyond-nearest-neighbor interactions and of always-resonant interactions.

Methods for renal lineage tracing: In vivo and beyond.

Lineage tracing has resulted in fundamental discoveries in kidney development and disease and remains a powerful technique to study mechanisms of organogenesis, homeostasis, and repair/regeneration. Following decades of research on the cellular and molecular regulation of renal organogenesis, the kidney has become one of the most well-characterized organs, resulting in exciting advancements in pluripotent stem cell differentiation, tissue bioengineering, and the potential for developing novel regenerative therapies for kidney disease. Lineage tracing, or the labeling of progeny cells arising from a single cell or group of cells, allows for spatial and temporal analyses of dynamic in vivo and in vitro processes. As lineage tracing techniques expand across disciplines of developmental biology, stem cell biology, and regenerative medicine, careful experimental design and interpretation, along with an understanding of the basic principles and technical limitations, are essential for utilizing genetically complex lineage tracing models to further understand kidney development and disease.