A murine model of Denys-Drash syndrome reveals novel transcriptional targets of WT1 in podocytes.

The Wilms tumor-suppressor gene WT1, a key player in renal development, also has a crucial role in maintenance of the glomerulus in the mature kidney. However, molecular pathways orchestrated by WT1 in podocytes, where it is highly expressed, remain unknown. Their defects are thought to modify the cross-talk between podocytes and other glomerular cells and ultimately lead to glomerular sclerosis, as observed in diffuse mesangial sclerosis (DMS) a nephropathy associated with WT1 mutations. To identify podocyte WT1 targets, we generated a novel DMS mouse line, performed gene expression profiling in isolated glomeruli and identified excellent candidates that may modify podocyte differentiation and growth factor signaling in glomeruli. Scel, encoding sciellin, a protein of the cornified envelope in the skin, and Sulf1, encoding a 6-O endosulfatase, are shown to be expressed in wild-type podocytes and to be strongly down-regulated in mutants. Co-expression of Wt1, Scel and Sulf1 was also found in a mesonephric cell line, and siRNA-mediated knockdown of WT1 decreased Scel and Sulf1 mRNAs and proteins. By ChIP we show that Scel and Sulf1 are direct WT1 targets. Cyp26a1, encoding an enzyme involved in the degradation of retinoic acid, is shown to be up-regulated in mutant podocytes. Cyp26a1 may play a role in the development of glomerular lesions but does not seem to be regulated by WT1. These results provide novel clues in our understanding of normal glomerular function and early events involved in glomerulosclerosis.

Spred-2 suppresses aorta-gonad-mesonephros hematopoiesis by inhibiting MAP kinase activation.

In midgestation mouse embryos, the aorta-gonad-mesonephros (AGM) region generates hematopoietic stem cells and definitive hematopoiesis is regulated by cell-cell interaction and signaling molecules. We showed that a Ras/mitogen-activated protein (MAP) kinase signaling-specific inhibitor and a dominant negative mutant Ras blocked the production of CD45+ hematopoietic cells in embryonic day 11.5 AGM culture, indicating an essential role for the MAP kinase pathway in AGM hematopoiesis. Overexpression of the Ras/MAP kinase pathway regulator, Spred-2, in the AGM culture significantly reduced the number of CD45+ cells. In contrast, production of CD45+ cells from the AGM region of Spred-2-null mice was up-regulated as compared with wild-type littermates. Furthermore, Spred-2-deficient mice exhibited elevated hematopoietic colony formation from vascular endothelial-cadherin+ cells. These data indicate that Spred-2 functions as a negative regulator of AGM hematopoiesis by inhibiting hematopoietic cytokine signaling.

LIM kinase function and renal growth: Potential role for LIM kinases in fetal programming of kidney development.

AIMS: Maternal dietary restriction during pregnancy impairs nephron development and results in offspring with fewer nephrons. Cell turnover in the early developing kidney is altered by exposure to maternal dietary restriction and may be regulated by the LIM-kinase family of enzymes. We set out to establish whether disturbance of LIM-kinase activity might play a role in the impairment of nephron formation. MAIN METHODS: E12.5 metanephric kidneys and HK2 cells were grown in culture with the pharmacological LIM-kinase inhibitor BMS5. Organs were injected with DiI, imaged and cell numbers measured over 48h to assess growth. Cells undergoing mitosis were visualised by pH3 labelling. KEY FINDINGS: Growth of cultured kidneys reduced to 83% of controls after exposure to BMS5 and final cell number to 25% of control levels after 48h. Whilst control and BMS5 treated organs showed cells undergoing mitosis (100±11 cells/field vs 113±18 cells/field respectively) the proportion in anaphase was considerably diminished with BMS5 treatment (7.8±0.8% vs 0.8±0.6% respectively; P<0.01). This was consistent with effects on HK2 cells highlighting a severe impact of BMS5 on formation of the mitotic spindle and centriole positioning. DiI labelled cells migrated in 100% of control cultures vs 0% BMS5 treated organs. The number of nephrogenic precursor cells appeared depleted in whole organs and formation of new nephrons was blocked by exposure to BMS5. SIGNIFICANCE: Pharmacological blockade of LIM-kinase function in the early developing kidney results in failure of renal development. This is likely due to prevention of dividing cells from completion of mitosis with their resultant loss.

Cloning and characterization of a full-length cDNA coding for ovine aldolase B from fetal mesonephros.

An ovine aldolase B cDNA was isolated from mesonephros (29 d pc). The sequence covers 1649 nucleotides. Comparison with human liver aldolase B cDNA shows a homology of about 86%. The deduced amino acid sequence is composed of 364 residues and exhibits 92% homology to the human protein. Northern blot analysis and in situ hybridization data show that during the first third of gestation in sheep, aldolase B expression is restricted to the mesonephros.

Renal carbonic anhydrase in the quail Coturnix coturnix japonica. II. Changes of enzyme activity in developing and regressing mesonephros.

Carbonic anhydrase activity was studied during development and regression of the quail mesonephros by in situ and extra situm investigation. A close correlation was noted between enzyme expression and tissue morphofunctional state. Carbonic anhydrase appears in early development; its highest activity is reached when the kidney is actively secreting, followed by a decrease concomitant with tissue involution. The main localization of the reaction product is the distal tubule showing strongly positive cells intercalated with clear, negative ones. In the functional organ, staining was found at the level of transitional and connecting segments and Wolffian duct. The comparison with the histochemical pattern of the quail metanephros suggests that the functional meaning of renal carbonic anhydrase might be the same both in transitory and in permanent kidney.

The pig mesonephros. I. Enzyme histochemical observations on the segmentation of the nephron.

Cryostat sections from the mesonephros of various pig embryos with a crown-rump-length of between 17 and 95 mm were used for light microscopical assays of acid hydrolases (acid phosphatase, beta-D-N-acetylglucosaminidase, beta-D-glucuronidase), oxidoreductases (succinic dehydrogenase, NADH- and NADPH-tetrazolium reductase) and adenosine triphosphatases (Mg2+- and Na+--K+-ATPase). Our main intention was to distinguish more accurately between the different parts of the pig's nephron, which is exceedingly long and coiled. The proximal tubule, that exhibits a high activity for acid phosphatase but none in beta-D-glucuronidase incubations, shows no subsegmentation apart from a stronger reaction of its initial segment that was apparent in three of our assays. In the distal tubule, a preattachment convolution, an attachment zone, and a postattachment coil can be discriminated by a synopsis of all histiograms. The beginning of the collecting tubule is situated in the middle of the organ and not at its dorsal face as was previously believed. Up to three different segments can be discriminated in the collecting tubule. The distal and the collecting tubule harbor on ouabain-sensitive Na+--K+-ATPase activity which decreases considerably towards the Wolffian duct. The enzymatic maturation of the mesonephric pig nephron is almost completed in 17 mm embryos.

The significance of rudimentary nephrostomial tubules for the origin of the vertebrate gonad.

Initial gonadal development was studied in 30- to 40-day-old bovine embryos. The results were interpreted in conjunction with findings on pro- and mesonephric organization in larval forms of Ichthyophis kohtaoensis (Gymnophiona, Amphibia). In bovine embryos vestigial nephrostomial tubules are the immediate precursors of the blastemas for adrenocortical, rete, gonadal and Mullerian infundibular development. From the study of Ichthyophis it can be concluded that the vestigial nephrostomial tubules seen in the bovine embryo are pronephric and not mesonephric in nature. As a consequence, the indifferent mammalian gonad is defined as a modified homologue of the pronephros situated in the zone of pro-/mesonephric overlapping. Such an overlapping of the two kidney generations in the fully developed state is clearly seen in Ichthyophis. Overlapping of the mesonephros with the modified pronephros (gonad) is necessary to allow intercalation of mesonephric tubules (efferent ductules in mammals) into the male seminal excurrent duct system.

Renal ontogeny: epithelial transport in the mammalian mesonephric proximal tubule.

The role of the mammalian mesonephric kidney is not completely understood. It has been established that outpouchings of the mesonephric excretory ducts give origin to parts of the urogenital system of the adult. It is also known that mammalian mesonephric urine is formed as an ultrafiltrate. The mesonephric renal tubules have Na+/K+ adenosine triphosphatase (Na+/K+ pump), secrete phenol red, and reabsorb protein. Prior to this work, the possibility of epithelial transport of ions and metabolic substrates across mammalian mesonephric tubules had not been directly evaluated. Proximal mesonephric tubules obtained from 17 to 18-days-old rabbit embryos were isolated and perfused in vitro. Continuous intracellular electrical recordings were obtained with Ling-Gerard-type microelectrodes and a high input impedance electrometer. In tubules perfused and bathed in standard mammalian Ringer's solutions, the average transmembrane electrical cell potential difference (PD) was -43 +/- 0.5 mV (76 cells). The cellular PD decreased by 30 percent when the temperature of the bath was cooled from 37 degrees C to 30 degrees C. The cells also depolarized by 25 percent in the first five minutes of exposure to 0.1 mM ouabain. In addition, the cell PD decreased by 40 and 60 percent when the extracellular potassium concentration was raised from five to 25 and 50 mM, respectively. The uptake of glucose and alanine was similarly electrogenic (delta:1 mV/mM). The cell PD, the K+ conductance, and the electrogenicity induced by luminal exposure to 5 mM glucose or alanine are significantly lower in the mesonephric as compared to the metanephric proximal tubules of the rabbit. These observations suggest that sodium-coupled transepithelial transport mechanisms, driven by the Na+/K+ pump, are already present in the mammalian mesonephric proximal tubule. Increases in the number of Na+/K+ pumps, conductive K+ channels, and sodium-substrate cotransporters seem to be at the core of proximal tubular ontogeny.

[Histochemical localization of carbonic anhydrase in flask cells of the clawfrog mesonephros (Xenopus laevis Daudin) (author's transl)]. / Histochemischer Nachweis von Carboanhydrase in den Flaschenzellen der Nieren vom Krallenfrosch (Xenopus laevis Daudin).

Carbonic anhydrase activity was demonstrated in the flask cells of intermediate segments and collecting tubules of the clawfrog-mesonephros with the cobalt-bicarbonate method of Häusler (1958) and Hansson (1967). Additional the luminal surface of proximal and distal convoluted tubules reacted positively. By electron microscopy the enzyme activity in the flask cells was localized mainly on the surface of microvilli like cytoplasmic processes which lined the lumen of intracellular secretion capillaries. The existence of carbonic anhydrase in the flask cells is related to a possible physiological function of these cells.

Functional specialization of the epithelium in the mesonephric tubules.

An electron microscopy study was aimed to correlate structural differentiation of the epithelium in mesonephric proximal tubules (PT) with the expression of membrane activities of alkaline phosphatase (AP) and 5'-nucleotidase (AMP). Tissue samples of mesonephros were taken from 5 to 16 days old chick embryos. Both enzymes were detected with cerium technique, Mayahara modification of lead capture method was used also for localization of AP. Control incubation was performed with levamisole. The formation of absorptive apparatus was characterized by the differentiation of PT epithelium. Activities of AP and AMP appeared to increase rapidly with the differentiation of epithelium. Reaction products of AP and AMP were detected on brush border as well as on membranes of tubular invaginations, transport tubules and endocytotic vacuoles. The basolateral cell surfaces of epithelium were projected in short interdigitating microvilli and the expression of AP and AMP activities on their membranes suggested the transport role of this structural specialization.

An ultrastructural and cytochemical study of the mesonephros of Rana esculenta during activity and hibernation.

The biological cycle of most amphibians undergoes seasonal variations. In this study, we investigated the mesonephros of Rana esculenta during active life and the natural hibernation period. The ultrastructural morphology of the different tracts constituting the nephron was analysed. Moreover, to evaluate the effect of seasonal temperature variations on the mesonephros function, the activity of some enzymes linked to membrane transport and playing regulatory roles in various metabolic pathways was investigated in different tracts of the frog nephron. During hibernation the glomerular filtration barrier appeared thicker than in the active life, lysosomes and paraplasmatic material, mostly glycogen, being accumulated in the proximal and distal tubule cells respectively. Cytoplasmic organelles, i.e., mitochondria, endoplasmic reticulum were observed in segregated areas. At the same time, changes in some enzyme activities were noted. The activity of some membrane-transport enzymes (5' nucleotidase and K+-p-nitrophenyl phosphatase) and of energetic metabolism (succinic dehydrogenase) was reduced. Nevertheless the alkaline phosphatase activity was not changed significantly, and this suggests that some metabolic activities were preserved in the hibernating samples. These results indicate morpho-functional adaptations of the kidney cells that preserve their role in osmoregulation and some metabolic processes, even during unfavourable seasons.

[Succinate dehydrogenase activity in the mesonephros in the process of development of chick embryos]. / Aktivnost' suktsinatdegidrogenazy v mezonefrose v protsesse razvitiia émbrionov tsypliat.

The activity of succinate dehydrogenase in the mesonephros tissue of chick embryos is rather high on the 6th day of embryonal development and is not subjected to significant changes up to the 17th day. The absence of wide variations in the activity of this enzyme during the period of degeneration of the mesonephros may be due to a parallel decrease in the organ's mass and in the number of its mitochondria.

Mind bomb-1 is essential for intraembryonic hematopoiesis in the aortic endothelium and the subaortic patches.

Intraembryonic hematopoiesis occurs at two different sites, the floor of the aorta and subaortic patches (SAPs) of the para-aortic splanchnopleura (P-Sp)/aorta-gonad-mesonephros (AGM) region. Notch1 and RBP-jkappa are critical for the specification of hematopoietic stem cells (HSCs) in Notch signal-receiving cells. However, the mechanism by which Notch signaling is triggered from the Notch signal-sending cells to support embryonic hematopoiesis remains to be determined. We previously reported that Mind bomb-1 (Mib1) regulates Notch ligands in the Notch signal-sending cells (B. K. Koo, M. J. Yoon, K. J. Yoon, S. K. Im, Y. Y. Kim, C. H. Kim, P. G. Suh, Y. N. Jan, and Y. Y. Kong, PLoS ONE 2:e1221, 2007). Here, we show that intraembryonic hematopoietic progenitors were absent in the P-Sp of Mib1(-/-) embryos, whereas they were partly preserved in the Tie2-cre; Mib1(f)(/f) P-Sps, suggesting that Mib1 plays a role in the endothelium and the SAPs. Interestingly, dll1 and dll4/Jag1 are expressed in the SAPs and the endothelium of the AGM, respectively, where mib1 is detected. Indeed, Notch signaling was activated in the nascent HSCs at both sites. In the P-Sp explant culture, the overexpression of Dll1 in OP9 stromal cells rescued the failed production of hematopoietic progenitors in the Mib1(-/-) P-Sp, while its activity was abolished by Mib1 knockdown. These results suggest that Mib1 is important for intraembryonic hematopoiesis not only in the aortic endothelium but also in the SAPs.

Histochemical localization of Mg2+-Na+-K+-adenosine triphosphatase in different stages of the sheep mesonephros.

Mesonephroi of sheep embryos ranging from 12 to 100 mm C.R. length were examined for the occurrence and localization of transport-ATPase. Native cryostat sections were incubated according to the technique of Guth and Albers for demonstrating the nitrophenylphosphatase activity of Mg2+-Na+-K+-adenosine triphosphatase. The basal cytoplasm of the collecting tubule of the narrow segment of the distal tubule exhibit strong activity, the wide segment of the distal tubule is moderately active. Glomeruli, proximal tubule, and Wolffian duct remain unstained. The basal labyrinths of the reactive nephron segments are believed to be the sites of a Na+-K+ exchange pump. In mature and regressing mesonephroi, the findings fully agree with biochemical data; in maturating mesonephroi, whose basal labyrinth is not yet fully established, the biochemical assay proves to be more sensitive. The specifity of the reaction was ascertained by diverse inhibitors and activating ions. The localization of Mg2+-ATPase is different to the above mentioned reaction pattern, as it shows moderate activity in the proximal tubule, too (mature mesonephros). Mesonephroi of very young embryos exhibit strongest Mg2+-ATPase activity in the proximal tubule; here the distal and collecting tubule stain only moderately.

Enzyme histochemical investigation of glycol methacrylate embedded chick embryonic tissue.

The advantages of the water-soluble glycol methacrylate (GMA) embedding procedure make it highly applicable for use with fragile early embryonic material. Not only can one obtain tissue sections containing excellent histological detail, but numerous enzymes are retained for subsequent histochemical localization. For the purpose of establishing a methodology whereby concomitant histology and histochemistry could be obtainable, various fixatives and fixation times have been evaluated on GMA embedded chick embryonic mesonephros and gonad. It was found that fixing the tissues for 1 h in a solution of 95% ethanol, 5% acetic acid and 10% neutral-buffered formalin resulted in the retention of not only excellent histology but also alkaline and acid phosphatase. Thus, with this procedure, more specific investigations of early embryonic tissue can be performed.

Expression patterns of ammonia-metabolizing enzymes in the liver, mesonephros, and gut of human embryos and their possible implications.

Human and ungulate embryos can catabolize amino acids for energy production, whereas rodent embryos cannot, raising the question whether studies of rodent model systems are suitable for extrapolation to the human situation. Therefore, we investigated the expression of the amino acid- and ammonia-metabolizing enzymes glutaminase, glutamate dehydrogenase, glutamine synthase, carbamoylphosphate synthase, and arginase immunohistochemically in a graded series of human embryos and fetuses. During human development the expression of these enzymes is first seen in the liver, then in the mesonephric kidney, and finally in the small intestine. Such a simultaneous expression of nitrogen-metabolizing enzymes was not seen in any other organ. The early appearance of the enzymes involved in amino acid and ammonia metabolism in the human liver, compared to, for example, the rat liver, suggests that catabolism of amino acids may provide an important supply of metabolic energy for the human embryo. The coexpression of glutaminase, glutamate dehydrogenase, and carbamoylphosphate synthase, but not of arginase, in the mesonephros and the small intestine suggests that these organs are involved in the biosynthesis of intermediates of the ornithine cycle, e.g., arginine or citrulline. From a comparison of the developmental appearance of ornithine cycle enzymes in different mammalian species we postulate that an early appearance of these enzymes is generally associated with a relatively slow prenatal growth rate and the use of amino acids as metabolic fuel.

Steroidogenic enzyme activity and ovarian differentiation in the saltwater crocodile, Crocodylus porosus.

It has been hypothesized that steroid hormone production is involved in sexual differentiation of the gonads in reptiles with temperature-dependent sex determination. We have therefore examined steroidogenic enzymes and ovarian differentiation in Crocodylus porosus embryos incubated at 30 degrees, a temperature producing 100% female hatchlings. delta 5-3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) activity was detected only in the adrenal gland before, during, and after the period of ovary differentiation. The same pattern was observed during testis differentiation in embryos incubated at 32 degrees (predominantly male-producing). At no stage was 3 beta-HSD activity detected in the gonads. The tritiated water assay was used to measure aromatase enzyme activity in the gonad-adrenal-mesonephric complex (GAM) during development at 30 degrees C. Aromatase activity in the GAM increased during the period of ovary differentiation. In female C. porosus hatchlings, 85% of the aromatase activity within the GAM was derived from the ovary, 10% from the adrenal, and 5% from the regressing mesonephros. The aromatase inhibitors aminoglutethimide and 4-hydroxyandrostenedione significantly reduced aromatase activity in female hatchling GAMs. In some stage 25 embryos incubated at 32.5 degrees, aromatase activity was low in testes and high in ovaries. These observations show that urogenital tissues of C. porosus are steroidogenically active during gonadal differentiation and that increased aromatase enzyme activity accompanies ovary development at 30 degrees. Steroid synthesis in the GAM of C. porosus embryos may involve interaction between the adrenal glands and the gonads.

Beta-glucuronidase activity is present in the microscopic epididymis of the Tfm/Y mouse.

The sex-linked recessive gene Tfm in the mouse produces a condition of testicular feminization (androgen insensitivity syndrome, AIS) in hemizygotes, comparable to the condition of the same name in humans. The murine mutant was originally believed to have no derivatives of the mesonephric duct system (MDS), and this absence was ascribed to dependence of these derivatives on androgens for survival. However, microscopical epididymides, retia testes, and vasa deferentia were identified in these animals in our laboratory. These micro-organs may play a role in meiosis induction in Tfm/Y animals. The present study was designed to determine whether survival of these organs is due to retention of an ability to respond to androgens, or whether they are unique amongst MDS derivatives in being independent of androgens. Previous studies in our laboratory demonstrated that the enzyme beta-glucuronidase (beta G) is androgen sensitive in the epididymis of the normal mouse. In the present investigation we used this enzyme as a marker to study androgen sensitivity in the microscopical epididymides of Tfm/Y hemizygotes and in the epididymides of control +/Y litter-mate brothers. Both mutant and control animals were studied with and without exogenous androgen stimulation. Tfm/Y hemizygotes demonstrated low levels of diffuse, cytoplasmic beta G activity that appears to be unresponsive to exogenous androgen stimulation. In light of our previous studies, this distribution of beta G reaction products suggests some degree of androgen sensitivity. The survival of these micro-organs and their partial androgen sensitivity may be related to the role of the MDS in inducing meiosis.

The embryologic origin of the caput epididymidis in the rat.

The ACI rat with its known incidence of ipsilateral agenesis of the kidney and ductus deferens provides an excellent mammalian model for the study of the embryologic origin or the caput epididymidis. Because a portion of the caput epididymidis remains in these affected animals, it seems to be derived from the mesonephric tubules rather than the mesonephric duct in the rat. Histochemical assays also support the common origin of both the ductuli efferentes and caput epididymidis from the mesonephric tubules.