The molecular and cellular anatomy of a fetal programming defect - the impact of low protein diet on the developing kidney.

Low nephron number correlates with the development of hypertension and chronic kidney disease later in life. While intrauterine growth restriction caused by maternal low protein diet (LPD) is thought to be a significant cause of reduced nephron endowment in impoverished communities, its influence on the cellular and molecular processes which drive nephron formation are poorly understood. We conducted a comprehensive characterization of the impact of LPD on kidney development using tomographic and confocal imaging to quantify changes in branching morphogenesis and the cellular and morphological features of nephrogenic niches across development. These analyses were paired with single-cell RNA sequencing to dissect the transcriptional changes that LPD imposes during renal development. Differences in the expression of genes involved in metabolism were identified in most cell types we analyzed, yielding imbalances and shifts in cellular energy production. We further demonstrate that LPD impedes branching morphogenesis and significantly reduces the number of pretubular aggregates - the initial precursors to nephron formation. The most striking observation was that LPD changes the developmental trajectory of nephron progenitor cells, driving the formation of a partially committed cell population which likely reflects a failure of cells to commit to nephron formation and which ultimately reduces endowment. This unique profile of a fetal programming defect demonstrates that low nephron endowment arises from the pleiotropic impact of changes in branching morphogenesis and nephron progenitor cell commitment, the latter of which highlights a critical role for nutrition in regulating the cell fate decisions underpinning nephron endowment. Significance Statement: While a mother's diet and behavior can negatively impact the number of nephrons in the kidneys of her offspring, the root cellular and molecular drivers of these deficits have not been rigorously explored. In this study we use advanced imaging and gene expression analysis in mouse models to define how a maternal low protein diet, analogous to that of impoverished communities, results in reduced nephron endowment. We find that low protein diet has pleiotropic effects on metabolism and the normal programs of gene expression. These profoundly impact the process of branching morphogenesis necessary to establish niches for nephron generation and change cell behaviors which regulate how and when nephron progenitor cells commit to differentiation.

Acetyl-CoA is a key molecule for nephron progenitor cell pool maintenance.

Nephron endowment at birth impacts long-term renal and cardiovascular health, and it is contingent on the nephron progenitor cell (NPC) pool. Glycolysis modulation is essential for determining NPC fate, but the underlying mechanism is unclear. Combining RNA sequencing and quantitative proteomics we identify 267 genes commonly targeted by Wnt activation or glycolysis inhibition in NPCs. Several of the impacted pathways converge at Acetyl-CoA, a co-product of glucose metabolism. Notably, glycolysis inhibition downregulates key genes of the Mevalonate/cholesterol pathway and stimulates NPC differentiation. Sodium acetate supplementation rescues glycolysis inhibition effects and favors NPC maintenance without hindering nephrogenesis. Six2Cre-mediated removal of ATP-citrate lyase (Acly), an enzyme that converts citrate to acetyl-CoA, leads to NPC pool depletion, glomeruli count reduction, and increases Wnt4 expression at birth. Sodium acetate supplementation counters the effects of Acly deletion on cap-mesenchyme. Our findings show a pivotal role of acetyl-CoA metabolism in kidney development and uncover new avenues for manipulating nephrogenesis and preventing adult kidney disease.

The potential impact of PM2.5 on the covid-19 crisis in the Brazilian Amazon region.

OBJECTIVE: This study aims to assess covid-19 morbidity, mortality, and severity from 2020 to 2021 in five Brazilian Amazon states with the highest records of wildfires. METHODS: A distributed lag non-linear model was applied to estimate the potential exposure risk association with particulate matter smaller than 2.5-µm in diameter (PM2.5). Daily mean temperature, relative humidity, percentual of community mobility, number of hospital beds, days of the week, and holidays were considered in the final models for controlling the confounding factors. RESULTS: The states of Para, Mato Grosso, and Amazonas have reported the highest values of overall cases, deaths, and severe cases of covid-19. The worrying growth in the percentual rates in 2020/2021 for the incidence, severity, and mortality were highlighted in Rondônia and Mato Grosso. The growth in 2020/2021 in the estimations of PM2.5 concentrations was higher in Mato Grosso, with an increase of 24.4%, followed by Rondônia (14.9%). CONCLUSION: This study establishes an association between wildfire-generated PM2.5 and increasing covid-19 incidence, mortality, and severity within the studied area. The findings showed that the risk of covid-19 morbidity and mortality is nearly two times higher among individuals exposed to high concentrations of PM2.5. The attributable fraction to PM2.5 in the studied area represents an important role in the risk associated with covid-19 in the Brazilian Amazon region.

Gene length is a pivotal feature to explain disparities in transcript capture between single transcriptome techniques.

The scale and capability of single-cell and single-nucleus RNA-sequencing technologies are rapidly growing, enabling key discoveries and large-scale cell mapping operations. However, studies directly comparing technical differences between single-cell and single-nucleus RNA sequencing are still lacking. Here, we compared three paired single-cell and single-nucleus transcriptomes from three different organs (Heart, Lung and Kidney). Differently from previous studies that focused on cell classification, we explored disparities in the transcriptome output of whole cells relative to the nucleus. We found that the major cell clusters could be recovered by either technique from matched samples, but at different proportions. In 2/3 datasets (kidney and lung) we detected clusters exclusively present with single-nucleus RNA sequencing. In all three organ groups, we found that genomic and gene structural characteristics such as gene length and exon content significantly differed between the two techniques. Genes recovered with the single-nucleus RNA sequencing technique had longer sequence lengths and larger exon counts, whereas single-cell RNA sequencing captured short genes at higher rates. Furthermore, we found that when compared to the whole host genome (mouse for kidney and lung datasets and human for the heart dataset), single transcriptomes obtained with either technique skewed from the expected proportions in several points: a) coding sequence length, b) transcript length and c) genomic span; and d) distribution of genes based on exons counts. Interestingly, the top-100 DEG between the two techniques returned distinctive GO terms. Hence, the type of single transcriptome technique used affected the outcome of downstream analysis. In summary, our data revealed both techniques present disparities in RNA capture. Moreover, the biased RNA capture affected the calculations of basic cellular parameters, raising pivotal points about the limitations and advantages of either single transcriptome techniques.

Chromatin-Accessible miRNA Regulons Driving Thyroid Tumorigenesis and Progression.

BACKGROUND: Although papillary thyroid cancer can remain indolent, associated lymph node metastases and recurrence rates are approximately 50% and 20%, respectively. Omics-based medicine has led to the discovery of predictive biomarkers that can be used to predict tumor progression and clinical outcomes. We aimed to develop a noninvasive omics-driven blood test to allow accurate risk stratification and help tailor individual patient treatment plans. STUDY DESIGN: RNA sequencing (seq) and microRNA analysis of The Cancer Genome Atlas and Gene Expression Omnibus datasets were employed to identify an epigenetic prognostic panel. Integrated bulk assay for transposase-accessible chromatin-seq and RNA-seq experiments confirmed the results. Sixty-two paired tumor and adjacent control thyroid tissues and 67 blood samples (62 papillary thyroid cancer and 5 controls) were analyzed for validation using sequencing and real-time polymerase chain reaction and correlated to clinical outcomes. A liposome-exosome fusion clustered regularly interspaced short palindromic repeats (CRISPR)-fluorescent detection system miRNA assay was developed. A predictive risk nomogram was generated and tested for performance. RESULTS: Our miRNA panel (miR-146b-5p and miR-221-3p) from tissue and blood was associated with aggressive features and was located within accessible chromatin regions. The miRNA risk score and prognostic nomogram showed higher accuracy in predicting lymph node metastases (miR-146b: area under the curve [AUC] 0.816, sensitivity 76.9%; miR-221: AUC 0.740, sensitivity 79.5%) and recurrence (miR-146b: AUC 0.921, sensitivity 75.0%; miR-221: AUC 0.756, sensitivity 70.0%; p < 0.001) than staging and American Thyroid Association risk stratification. CRISPR-based miRNA assays showed upregulation in the blood of cancer cohorts. CONCLUSIONS: CRISPR-based detection of miR-146b and miR-221 in the blood of thyroid cancer patients is a reliable and noninvasive tool for real-time assessment and prognostication that has great potential to provide a direct impact on the care of these patients.

The potential impact of PM2.5 on the covid-19 crisis in the Brazilian Amazon region

ABSTRACT OBJECTIVE This study aims to assess covid-19 morbidity, mortality, and severity from 2020 to 2021 in five Brazilian Amazon states with the highest records of wildfires. METHODS A distributed lag non-linear model was applied to estimate the potential exposure risk association with particulate matter smaller than 2.5-µm in diameter (PM2.5). Daily mean temperature, relative humidity, percentual of community mobility, number of hospital beds, days of the week, and holidays were considered in the final models for controlling the confounding factors. RESULTS The states of Para, Mato Grosso, and Amazonas have reported the highest values of overall cases, deaths, and severe cases of covid-19. The worrying growth in the percentual rates in 2020/2021 for the incidence, severity, and mortality were highlighted in Rondônia and Mato Grosso. The growth in 2020/2021 in the estimations of PM2.5 concentrations was higher in Mato Grosso, with an increase of 24.4%, followed by Rondônia (14.9%). CONCLUSION This study establishes an association between wildfire-generated PM2.5 and increasing covid-19 incidence, mortality, and severity within the studied area. The findings showed that the risk of covid-19 morbidity and mortality is nearly two times higher among individuals exposed to high concentrations of PM2.5. The attributable fraction to PM2.5 in the studied area represents an important role in the risk associated with covid-19 in the Brazilian Amazon region.

A miRNA-Based Prognostic Model to Trace Thyroid Cancer Recurrence.

Papillary thyroid carcinomas (PTCs) account for most endocrine tumors; however, screening and diagnosing the recurrence of PTC remains a clinical challenge. Using microRNA sequencing (miR-seq) to explore miRNA expression profiles in PTC tissues and adjacent normal tissues, we aimed to determine which miRNAs may be associated with PTC recurrence and metastasis. Public databases such as TCGA and GEO were utilized for data sourcing and external validation, respectively, and miR-seq results were validated using quantitative real-time PCR (qRT-PCR). We found miR-145 to be significantly downregulated in tumor tissues and blood. Deregulation was significantly related to clinicopathological features of PTC patients including tumor size, lymph node metastasis, TNM stage, and recurrence. In silico data analysis showed that miR-145 can negatively regulate multiple genes in the TC signaling pathway and was associated with cell apoptosis, proliferation, stem cell differentiation, angiogenesis, and metastasis. Taken together, the current study suggests that miR-145 may be a biomarker for PTC recurrence. Further mechanistic studies are required to uncover its cellular roles in this regard.

Single-Cell Transcriptome Analysis of the Circle of Willis in a Mouse Cerebral Aneurysm Model.

BACKGROUND: The circle of Willis (CoW) is the most common location for aneurysms to form in humans. Although the major cell types of the intracranial vasculature are well known, the heterogeneity and relative contributions of the different cells in healthy and aneurysmal vessels have not been well characterized. Here, we present the first comprehensive analysis of the lineage heterogeneity and altered transcriptomic profiles of vascular cells from healthy and aneurysmal mouse CoW using single-cell RNA sequencing. METHODS: Cerebral aneurysms (CAs) were induced in adult male mice using an elastase model. Single-cell RNA sequencing was then performed on CoW samples obtained from animals that either had aneurysms form or rupture 14 days post-induction. Sham-operated animals served as controls. RESULTS: Unbiased clustering analysis of the transcriptional profiles from >3900 CoW cells identified 19 clusters representing ten cell lineages: vascular smooth muscle cells, endothelial cells fibroblasts, pericytes and immune cells (macrophages, T and B lymphocytes, dendritic cells, mast cells, and neutrophils). The 5 vascular smooth muscle cell subpopulations had distinct transcriptional profiles and were classified as proliferative, stress-induced senescent, quiescent, inflammatory-like, or hyperproliferative. The transcriptional signature of the metabolic pathways of ATP generation was found to be downregulated in 2 major vascular smooth muscle cell clusters when CA was induced. Aneurysm induction led to significant expansion of the total macrophage population, and this expansion was further increased with rupture. Both inflammatory and resolution-phase macrophages were identified, and a massive spike of neutrophils was seen with CA rupture. Additionally, the neutrophil-to-lymphocyte ratio (NLR), which originated from CA induction mirrored what happens in humans. CONCLUSIONS: Our data identify CA disease-relevant transcriptional signatures of vascular cells in the CoW and is searchable via a web-based R/shiny interface.

Metabolic programming of nephron progenitor cell fate.

Metabolic pathways are one of the first responses at the cellular level to maternal/fetal interface stressors. Studies have revealed the previously unrecognized contributions of intermediary metabolism to developmental programs. Here, we provide an overview of cellular metabolic pathways and the cues that modulate metabolic states. We discuss the developmental and physiological implications of metabolic reprogramming and the key role of metabolites in epigenetic and epiproteomic modifications during embryonic development and with respect to kidney development and nephrogenesis.

Extracellular Vesicles Derived from Induced Pluripotent Stem Cells Promote Renoprotection in Acute Kidney Injury Model.

Induced pluripotent stem cells (iPSC) have been the focus of several studies due to their wide range of application, including in cellular therapy. The use of iPSC in regenerative medicine is limited by their tumorigenic potential. Extracellular vesicles (EV) derived from stem cells have been shown to support renal recovery after injury. However, no investigation has explored the potential of iPSC-EV in the treatment of kidney diseases. To evaluate this potential, we submitted renal tubule cells to hypoxia-reoxygenation injury, and we analyzed cell death rate and changes in functional mitochondria mass. An in vivo model of ischemia-reperfusion injury was used to evaluate morphological and functional alterations. Gene array profile was applied to investigate the mechanism involved in iPSC-EV effects. In addition, EV derived from adipose mesenchymal cells (ASC-EV) were also used to compare the potential of iPSC-EV in support of tissue recovery. The results showed that iPSC-EV were capable of reducing cell death and inflammatory response with similar efficacy than ASC-EV. Moreover, iPSC-EV protected functional mitochondria and regulated several genes associated with oxidative stress. Taken together, these results show that iPSC can be an alternative source of EV in the treatment of different aspects of kidney disease.

Complexity of the Wnt/ß­catenin pathway: Searching for an activation model.

Wnt signaling refers to a conserved signaling pathway, widely studied due to its roles in cellular communication, cell fate decisions, development and cancer. However, the exact mechanism underlying inhibition of the GSK phosphorylation towards ß-catenin and activation of the pathway after biding of Wnt ligand to its cognate receptors at the plasma membrane remains unclear. Wnt target genes are widely spread over several animal phyla. They participate in a plethora of functions during the development of an organism, from axial specification, gastrulation and organogenesis all the way to regeneration and repair in adults. Temporal and spatial oncogenetic re-activation of Wnt signaling almost certainly leads to cancer. Wnt signaling components have been extensively studied as possible targets in anti-cancer therapies. In this review we will discuss one of the most intriguing questions in this field, that is how ß-catenin, a major component in this pathway, escapes the destruction complex, gets stabilized in the cytosol and it is translocated to the nucleus where it acts as a co-transcription factor. Four major models have evolved during the past 20years. We dissected each of them along with current views and future perspectives on this pathway. This review will focus on the molecular mechanisms by which Wnt proteins modulate ß-catenin cytoplasmic levels and the relevance of this pathway for the development and cancer.

Extra-embryonic Wnt3 regulates the establishment of the primitive streak in mice.

The establishment of the head to tail axis at early stages of development is a fundamental aspect of vertebrate embryogenesis. In mice, experimental embryology, genetics and expression studies have suggested that the visceral endoderm, an extra-embryonic tissue, plays an important role in anteroposterior axial development. Here we show that absence of Wnt3 in the posterior visceral endoderm leads to delayed formation of the primitive streak and that interplay between anterior and posterior visceral endoderm restricts the position of the primitive streak. Embryos lacking Wnt3 in the visceral endoderm, however, appear normal by E9.5. Our results suggest a model for axial development in which multiple signals are required for anteroposterior axial development in mammals.

Biphasic regulation of type II phosphatidylinositol-4 kinase by sphingosine: cross talk between glycero- and sphingolipids in the kidney.

Phosphatidylinositol-4 kinase (PI-4K) is responsible for the generation of phosphatidylinositol-4 phosphate (PtdIns(4)P), a bioactive signaling molecule involved in several biological functions. In this study, we show that sphingosine modulates the activity of the PI-4K isoform associated with the basolateral membranes (BLM) from kidney proximal tubules. Immunoblotting with an anti-α subunit PI-4K polyclonal antibody revealed the presence of two bands of 57 and 62kDa in the BLM. BLM-PI-4K activity retains noteworthy biochemical properties; it is adenosine-sensitive, not altered by wortmanin, and significantly inhibited by Ca(2+) at the µM range. Together, these observations indicate the presence of a type II PI-4K. Endogenous phosphatidylinositol (PI) alone reaches PI-4K half-maximal activity, revealing that even slight modifications in PI levels at the membrane environment promote significant variations in BLM-associated-PI-4K activity. ATP-dependence assays suggested that the Mg.ATP(2-) complex is the true substrate of the enzyme and that free Mg(2+) is an essential cofactor. Another observation indicated that higher concentrations of free ATP are inhibitory. BLM-associated-PI-4K activity was ~3-fold stimulated in the presence of increasing concentration of sphingosine, while in concentrations higher than 0.4mM, in which S1P is pronouncedly formed, there was an inhibitory effect on PtdIns(4)P formation. We propose that a tightly coupled regulatory network involving phosphoinositides and sphingolipids participate in the regulation of key physiological processes in renal BLM carried out by PI-4K.

Wnt3 function in the epiblast is required for the maintenance but not the initiation of gastrulation in mice.

The formation of the anteroposterior axis in mice requires a Wnt3-dependent symmetry-breaking event that leads to the formation of the primitive streak and gastrulation. Wnt3 is expressed sequentially in two distinct areas of the mouse embryo before the appearance of the primitive streak; first in the posterior visceral endoderm and soon after in the adjacent posterior epiblast. Hence, although an axial requirement for Wnt3 is well established, its temporal and tissue specific requirements remain an open question. Here, we report the conditional inactivation of Wnt3 in the epiblast of developing mouse embryos. Contrary to previous studies, our data shows that embryos lacking Wnt3 specifically in the epiblast are able to initiate gastrulation and advance to late primitive streak stages but fail to thrive and are resorbed by E9.5. At the molecular level, we provide evidence that Wnt3 regulates its own expression and that of other primitive streak markers via activation of the canonical Wnt signaling pathway.

Catalase, Bax and p53 expression in the visual system of the crab Ucides cordatus following exposure to ultraviolet radiation.

In invertebrates, a few studies have suggested apoptosis as the mechanism of choice to protect the retina after exposure to ultraviolet (UV) radiation. We demonstrated previously, by electron microscopy, that the retina and lamina ganglionaris (or lamina) cells of the crab Ucides cordatus displayed subcellular signs of apoptosis after exposure to UVB and UVC. Here, we first ascertained, by the TdT-mediated dUTP-biotin nick end-labeling (TUNEL) technique, that UV irradiation indeed produced the previously reported results. We next tested, in the visual system of U. cordatus, whether the expression (as analyzed by immunohistochemistry and observed with laser scanning microscopy) and levels (as examined by Western blotting) of catalase, Bax, and p53 were affected by the same dose of UV radiation as that used previously. Our data revealed that the intensity of catalase, Bax, and p53 labeling was stronger in irradiated retina and lamina cells than in non-irradiated retina and lamina. However, no significant difference was observed in the concentrations of these proteins isolated from the whole optic lobe. The results thus suggest that UVB and UVC induce apoptosis in the crustacean retina and lamina by increasing catalase expression and activating the Bax- and p53-mediated apoptosis pathways.

Ca2+/calmodulin-dependent protein kinase II is an essential mediator in the coordinated regulation of electrocyte Ca2+-ATPase by calmodulin and protein kinase A.

The aim of this study was to investigate (a) whether Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) participates in the regulation of plasma membrane Ca2+-ATPase and (b) its possible cross-talk with other kinase-mediated modulatory pathways of the pump. Using isolated innervated membranes of the electrocytes from Electrophorus electricus L., we found that stimulation of endogenous protein kinase A (PKA) strongly phosphorylated membrane-bound CaM kinase II with simultaneous substantial activation of the Ca2+ pump (approximately 2-fold). The addition of cAMP (5-50 pM), forskolin (10 nM), or cholera toxin (10 or 100 nM) stimulated both CaM kinase II phosphorylation and Ca2+-ATPase activity, whereas these activation processes were cancelled by an inhibitor of the PKA alpha-catalytic subunit. When CaM kinase II was blocked by its specific inhibitor KN-93, the Ca2+-ATPase activity decreased to the levels measured in the absence of calmodulin; the unusually high Ca2+ affinity dropped 2-fold; and the PKA-mediated stimulation of Ca2+-ATPase was no longer seen. Hydroxylamine-resistant phosphorylation of the Ca2+-ATPase strongly increased when the PKA pathway was activated, and this phosphorylation was suppressed by inhibition of CaM kinase II. We conclude that CaM kinase II is an intermediate in a complex regulatory network of the electrocyte Ca2+ pump, which also involves calmodulin and PKA.

Cholesterol depletion by methyl-beta-cyclodextrin enhances myoblast fusion and induces the formation of myotubes with disorganized nuclei.

The formation of a skeletal muscle fiber begins with the withdrawal of committed mononucleated precursors from the cell cycle. These myoblasts elongate while aligning with each other, guided by recognition between their membranes. This step is followed by cell fusion and the formation of long striated multinucleated myotubes. We used methyl-beta-cyclodextrin (MCD) in primary cultured chick skeletal muscle cells to deplete membrane cholesterol and investigate its role during myogenesis. MCD promoted a significant increase in the expression of troponin T, enhanced myoblast fusion, and induced the formation of large multinucleated myotubes with nuclei being clustered centrally and not aligned at the cell periphery. MCD myotubes were striated, as indicated by sarcomeric alpha-actinin staining, and microtubule and desmin filament distribution was not altered. Pre-fusion MCD-treated myoblasts formed large aggregates, with cadherin and beta-catenin being accumulated in cell adhesion contacts. We also found that the membrane microdomain marker GM1 was not present as clusters in the membrane of MCD-treated myoblasts. Our data demonstrate that cholesterol is involved in the early steps of skeletal muscle differentiation.

Glial fibrillary acidic protein (GFAP)-like immunoreactivity in the visual system of the crab Ucides cordatus (Crustacea, Decapoda).

Glial fibrillary acidic protein (GFAP) is the main intermediate filament protein used as a marker for the identification of astrocytes in the central nervous system of vertebrates. Analogous filaments have been observed in the glial cells of many mollusks and annelids but not in crustaceans. The present study was carried out to identify by light microscopy immunohistochemistry, immunoelectronmicroscopy and immunoblotting, GFAP-like positive structures in the visual system of the crab Ucides cordatus as additional information to help detect and classify glial cells in crustaceans. Conventional electron microscopy, light microscopy of semithin sections and fluorescence light microscopy were also employed to characterize cells and tissues morphology. Our results indicated the presence of GFAP-like positive cell processes and cell bodies in the retina and adjoining optic lobe. The labeling pattern on the reactive profiles was continuous and very well defined, differing considerably from what has been previously reported in the central nervous system of some mollusks, where a diffuse spotted fluorescence pattern of labeling was observed. We suggest that this glial filament protein may be conserved in the evolution of the invertebrate nervous systems and that it may be used as a label for some types of glial cells in the crab.

Identification of a neurofilament-like protein in the protocerebral tract of the crab Ucides cordatus.

Neurofilaments (NFs) have not been observed in crustaceans using conventional electron microscopy, and intermediate filaments have never been described in crustaceans and other arthropods by immunocytochemistry. Since polypeptides, labeled by the NN18-clone antibody, were revealed on microtubule side-arms of crayfish, we have tested, in this study, whether proteins similar to mammalian NFs are present in the protocerebral tract (PCT) of the crab Ucides cordatus. We used immunohistochemistry for light microscopy with monoclonal antibodies against three different NF subunits, high (NF-H), medium (NF-M), and light (NF-L). Labeling was observed with the NN18-clone, which recognizes NF-M. In order to confirm the results obtained with the immunohistochemical reactions, Western blotting, using the three primary antibodies, was performed and the presence of NF-M was confirmed. The NN18-clone monoclonal antibody recognized a protein of approximately 160 kDa, similar to the mammalian NF-M protein, but NF-L and NF-H were not recognized. Conventional transmission electron microscopy was used to observe the ultrastructural components of the axons and immunoelectron microscopy was used to show the distribution of the NF-M-like polypeptides along cytoskeletal elements of the PCT. Our results agree with previous studies on crustacean NF proteins that have reported negative immunoreactions against NF-H and NF-L subunits and positive immunoreactions against the mammalian NF-M subunit. However, the protein previously referred to as P600 and recognized by the NN18-clone, has a very high molecular weight, thus, being different from mammalian NF-M subunit and from the protein revealed now in our study.

The plasma membrane Ca2+ pump from proximal kidney tubules is exclusively localized and active in caveolae.

Plasma membrane Ca2+-ATPase is involved in the fine-tuned regulation of intracellular Ca2+. In this study, the presence of Ca2+-ATPase in caveolae from kidney basolateral membranes was investigated. With the use of a discontinuous sucrose gradient, we show that Ca2+-ATPase is exclusively located and fully active in caveolin-containing microdomains. Treatment with methyl-beta-cyclodextrin--a cholesterol chelator--leads to a spreading of both caveolin and completely inactive Ca2+-ATPase toward high-density fractions. These data support the view that Ca2+ fluxes mediated by Ca2+-ATPase in kidney epithelial cells occur only in caveolae, being strictly dependent on the integrity of these microdomains.