Imaging centrosomes and cilia in the mouse kidney

Ultrastructure expansion microscopy (U-ExM) of mouse and human kidneys for analysis of subcellular structures

Ultrastructure expansion microscopy (U-ExM) involves the physical magnification of specimens embedded in hydrogels, which allows for super-resolution imaging of subcellular structures using a conventional diffraction-limited microscope. Methods for expansion microscopy exist for several organisms, organs, and cell types, and used to analyze cellular organelles and substructures in nanoscale resolution. Here, we describe a simple step-by-step U-ExM protocol for the expansion, immunostaining, imaging, and analysis of cytoskeletal and organellar structures in kidney tissue. We detail the critical modified steps to optimize isotropic kidney tissue expansion, and preservation of the renal cell structures of interest. We demonstrate the utility of the approach using several markers of renal cell types, centrioles, cilia, the extracellular matrix, and other cytoskeletal elements. Finally, we show that the approach works well on mouse and human kidney samples that were preserved using different fixation and embedding conditions. Overall, this protocol provides a simple and cost-effective approach to analyze both preclinical and clinical renal samples in high detail, using conventional lab supplies and standard widefield or confocal microscopy.

Ultrastructure expansion microscopy (U-ExM) of mouse and human kidneys for analysis of subcellular structures

Ultrastructure expansion microscopy (U-ExM) involves the physical magnification of specimens embedded in hydrogels, which allows for super-resolution imaging of subcellular structures using a conventional diffraction-limited microscope. Methods for expansion microscopy exist for several organisms, organs, and cell types, and used to analyze cellular organelles and substructures in nanoscale resolution. Here, we describe a simple step-by-step U-ExM protocol for the expansion, immunostaining, imaging, and analysis of cytoskeletal and organellar structures in kidney tissue. We detail the critical modified steps to optimize isotropic kidney tissue expansion, and preservation of the renal cell structures of interest. We demonstrate the utility of the approach using several markers of renal cell types, centrioles, cilia, the extracellular matrix, and other cytoskeletal elements. Finally, we show that the approach works well on mouse and human kidney samples that were preserved using different fixation and storage conditions. Overall, this protocol provides a simple and cost-effective approach to analyze both pre-clinical and clinical renal samples in high detail, using conventional lab supplies and standard widefield or confocal microscopy.

Aberrant centrosome biogenesis disrupts nephron and collecting duct progenitor growth and fate resulting in fibrocystic kidney disease

Mutations that disrupt centrosome biogenesis or function cause congenital kidney developmental defects and fibrocystic pathologies. Yet how centrosome dysfunction results in the kidney disease phenotypes remains unknown. Here, we examined the consequences of conditional knockout of the ciliopathy gene Cep120, essential for centrosome duplication, in the nephron and collecting duct progenitor niches of the mouse embryonic kidney. Cep120 loss led to reduced abundance of both cap mesenchyme and ureteric bud populations, due to a combination of delayed mitosis, increased apoptosis and premature differentiation of progenitor cells. These defects resulted in dysplastic kidneys at birth, which rapidly formed cysts, displayed increased interstitial fibrosis and decline in kidney function. RNA sequencing of embryonic and postnatal kidneys from Cep120-null mice identified changes in the pathways essential for development, fibrosis and cystogenesis. Our study defines the cellular and developmental defects caused by centrosome dysfunction during kidney morphogenesis and identifies new therapeutic targets for patients with renal centrosomopathies.

Aberrant centrosome biogenesis disrupts nephron progenitor cell renewal and fate resulting in fibrocystic kidney disease

Mutations that disrupt centrosome structure or function cause congenital kidney developmental defects and fibrocystic pathologies. Yet, it remains unclear how mutations in proteins essential for centrosome biogenesis impact embryonic kidney development. Here, we examined the consequences of conditional deletion of a ciliopathy gene, Cep120 , in the two nephron progenitor niches of the embryonic kidney. Cep120 loss led to reduced abundance of both metanephric mesenchyme and ureteric bud progenitor populations. This was due to a combination of delayed mitosis, increased apoptosis, and premature differentiation of progenitor cells. These defects resulted in dysplastic kidneys at birth, which rapidly formed cysts, displayed increased interstitial fibrosis, and decline in filtration function. RNA sequencing of embryonic and postnatal kidneys from Cep120-null mice identified changes in pathways essential for branching morphogenesis, cystogenesis and fibrosis. Our study defines the cellular and developmental defects caused by centrosome dysfunction during kidney development, and identifies new therapeutic targets for renal centrosomopathies.

Highlights

Defective centrosome biogenesis in nephron progenitors causes:Reduced abundance of metanephric mesenchyme and premature differentiation into tubular structuresAbnormal branching morphogenesis leading to reduced nephron endowment and smaller kidneysChanges in cell-autonomous and paracrine signaling that drive cystogenesis and fibrosisUnique cellular and developmental defects when compared to Pkd1 knockout models.

Centrosome amplification disrupts renal development and causes cystogenesis

Supernumerary centrosomes are commonly observed in cystic kidneys, but whether they are a cause or consequence of cystogenesis is unknown. Dionne et al. demonstrate that centrosome amplification disrupts renal development and is sufficient to induce cystogenesis in vivo.

Centrosome number is tightly controlled to ensure proper ciliogenesis, mitotic spindle assembly, and cellular homeostasis. Centrosome amplification (the formation of excess centrosomes) has been noted in renal cells of patients and animal models of various types of cystic kidney disease. Whether this defect plays a causal role in cystogenesis remains unknown. Here, we investigate the consequences of centrosome amplification during kidney development, homeostasis, and after injury. Increasing centrosome number in vivo perturbed proliferation and differentiation of renal progenitors, resulting in defective branching morphogenesis and renal hypoplasia. Centrosome amplification disrupted mitotic spindle morphology, ciliary assembly, and signaling pathways essential for the function of renal progenitors, highlighting the mechanisms underlying the developmental defects. Importantly, centrosome amplification was sufficient to induce rapid cystogenesis shortly after birth. Finally, we discovered that centrosome amplification sensitized kidneys in adult mice, causing cystogenesis after ischemic renal injury. Our study defines a new mechanism underlying the pathogenesis of renal cystogenesis, and identifies a potentially new cellular target for therapy.