Developmental regulation and the role of insulin and insulin receptor in metanephrogenesis

Exposure to Gestational Diabetes Mellitus (GDM) alters DNA methylation in placenta and fetal cord blood

BACKGROUND

Fetal exposure to maternal GDM increases offspring risk for adult-onset metabolic syndromes. Epigenetic modifications such as DNA methylation are modulators for fetal metabolic programming and susceptibility to adult-onset disease. This study investigates genome-wide DNA methylation in GDM exposed cord blood and placenta.

METHODS

Oral glucose tolerance testing between 24 and 28 weeks of pregnancy was used to determine severity of glucose intolerance. We measured DNA methylation (DNAm) using the Illumina Infinium 450 K array in 42 fetal cord blood and 36 placenta samples.

RESULTS

We identified 662 and 99 CpG sites in GDM placenta and cord blood, respectively at p-value <0.01 and a methylation difference >5% after adjustment for confounders. Annotated sites for AHRR and PTPRN2 were common to cord blood and placenta. Adding published GDM cord blood DNAm data we segregated patients based on treatment (Diet Only vs. +Insulin) and identified altered CpG sites to be unique to each GDM treatment group.

CONCLUSION

Consistency in findings with other studies provides evidence for the role of DNAm in placental and fetal responses to hyperglycemia. However, segregating DNAm analysis of GDM samples based on treatment may help delineate whether observed DNAm alterations are reflective of adaptive responses or treatment effects in utero.

Defective insulin receptor signaling in hPSCs skews pluripotency and negatively perturbs neural differentiation

Human embryonic stem cells are a type of pluripotent stem cells (hPSCs) that are used to investigate their differentiation into diverse mature cell types for molecular studies. The mechanisms underlying insulin receptor (IR)-mediated signaling in the maintenance of human pluripotent stem cell (hPSC) identity and cell fate specification are not fully understood. Here, we used two independent shRNAs to stably knock down IRs in two hPSC lines that represent pluripotent stem cells and explored the consequences on expression of key proteins in pathways linked to proliferation and differentiation. We consistently observed lowered pAKT in contrast to increased pERK1/2 and a concordant elevation in pluripotency gene expression. ERK2 chromatin immunoprecipitation, luciferase assays, and ERK1/2 inhibitors established direct causality between ERK1/2 and OCT4 expression. Of importance, RNA sequencing analyses indicated a dysregulation of genes involved in cell differentiation and organismal development. Mass spectrometry–based proteomic analyses further confirmed a global downregulation of extracellular matrix proteins. Subsequent differentiation toward the neural lineage reflected alterations in SOX1⁺PAX6⁺ neuroectoderm and FOXG1⁺ cortical neuron marker expression and protein localization. Collectively, our data underscore the role of IR-mediated signaling in maintaining pluripotency, the extracellular matrix necessary for the stem cell niche, and regulating cell fate specification including the neural lineage.

Insulin receptor signaling regulates renal collecting duct and intercalated cell antibacterial defenses

People with diabetes mellitus have increased infection risk. With diabetes, urinary tract infection (UTI) is more common and has worse outcomes. Here, we investigate how diabetes and insulin resistance impact the kidney's innate defenses and urine sterility. We report that type 2 diabetic mice have increased UTI risk. Moreover, insulin-resistant prediabetic mice have increased UTI susceptibility, independent of hyperglycemia or glucosuria. To identify how insulin resistance affects renal antimicrobial defenses, we genetically deleted the insulin receptor in the kidney's collecting tubules and intercalated cells. Intercalated cells, located within collecting tubules, contribute to epithelial defenses by acidifying the urine and secreting antimicrobial peptides (AMPs) into the urinary stream. Collecting duct and intercalated cell-specific insulin receptor deletion did not impact urine acidification, suppressed downstream insulin-mediated targets and AMP expression, and increased UTI susceptibility. Specifically, insulin receptor-mediated signaling regulates AMPs, including lipocalin 2 and ribonuclease 4, via phosphatidylinositol-3-kinase signaling. These data suggest that insulin signaling plays a critical role in renal antibacterial defenses.

Insulin receptor-mediated signaling regulates pluripotency markers and lineage differentiation

Objectives

Insulin receptor (IR)-mediated signaling is involved in the regulation of pluripotent stem cells; however, its direct effects on regulating the maintenance of pluripotency and lineage development are not fully understood. The main objective of this study is to understand the role of IR signaling in pluripotency and lineage development.

Methods

To explore the role of IR signaling, we generated IR knock-out (IRKO) mouse induced pluripotent stem cells (miPSCs) from E14.5 mouse embryonic fibroblasts (MEFs) of global IRKO mice using a cocktail of four reprogramming factors: Oct4, Sox2, Klf4, cMyc. We performed pluripotency characterization and directed the differentiation of control and IRKO iPSCs into neural progenitors (ectoderm), adipocyte progenitors (mesoderm), and pancreatic beta-like cells (endoderm). We mechanistically confirmed these findings via phosphoproteomics analyses of control and IRKO iPSCs.

Results

Interestingly, expression of pluripotency markers including Klf4, Lin28a, Tbx3, and cMyc were upregulated, while abundance of Oct4 and Nanog were enhanced by 4-fold and 3-fold, respectively, in IRKO iPSCs. Analyses of signaling pathways demonstrated downregulation of phospho-STAT3, p-mTor and p-Erk and an increase in the total mTor and Erk proteins in IRKO iPSCs in the basal unstimulated state. Stimulation with leukemia inhibitory factor (LIF) showed a ∼33% decrease of phospho-ERK in IRKO iPSCs. On the contrary, Erk phosphorylation was increased during in vitro spontaneous differentiation of iPSCs lacking IRs. Lineage-specific directed differentiation of the iPSCs revealed that cells lacking IR showed enhanced expression of neuronal lineage markers (Pax6, Tubb3, Ascl1 and Oligo2) while exhibiting a decrease in adipocyte (Fas, Acc, Pparγ, Fabp4, C/ebpα, and Fsp27) and pancreatic beta cell markers (Ngn3, Isl1, and Sox9). Further molecular characterization by phosphoproteomics confirmed the novel IR-mediated regulation of the global pluripotency network including several key proteins involved in diverse aspects of growth and embryonic development.

Conclusion

We report, for the first time to our knowledge, the phosphoproteome of insulin, IGF1, and LIF stimulation in mouse iPSCs to reveal the importance of insulin receptor signaling for the maintenance of pluripotency and lineage determination.

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Insulin receptor signaling regulates expression of key pluripotency genes including Oct4 and Nanog.

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IRKO iPSCs show upregulation of neuronal markers during differentiation.

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Adipocyte and pancreatic beta cell differentiation are perturbed in IRKO iPSCs.

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Phosphoproteomics analyses confirmed the role of IR in regulation of pluripotency and developmental proteins.

Renal tubule insulin receptor modestly promotes elevated blood pressure and markedly stimulates glucose reabsorption

Although the cause of hypertension among individuals with obesity and insulin resistance is unknown, increased plasma insulin, acting in the kidney to increase sodium reabsorption, has been proposed as a potential mechanism. Insulin may also stimulate glucose uptake, but the contributions of tubular insulin signaling to sodium or glucose transport in the setting of insulin resistance is unknown. To directly study the role of insulin signaling in the kidney, we generated inducible renal tubule-specific insulin receptor-KO mice and used high-fat feeding and mineralocorticoids to model obesity and insulin resistance. Insulin receptor deletion did not alter blood pressure or sodium excretion in mice on a high-fat diet alone, but it mildly attenuated the increase in blood pressure with mineralocorticoid supplementation. Under these conditions, KO mice developed profound glucosuria. Insulin receptor deletion significantly reduced SGLT2 expression and increased urinary glucose excretion and urine flow. These data demonstrate a direct role for insulin receptor-stimulated sodium and glucose transport and a functional interaction of insulin signaling with mineralocorticoids in vivo. These studies uncover a potential mechanistic link between preserved insulin sensitivity and renal glucose handling in obesity and insulin resistance.

Genetic low nephron number hypertension is associated with dysregulation of the hepatic and renal insulin-like growth factor system during nephrogenesis

OBJECTIVE

Low nephron number may represent a major determinant of human primary hypertension in adult life. This hypothesis is supported by a genetic rat model, namely the Munich-Wistar-Frömter (MWF) rat, which demonstrates an inherited deficit in nephron number and the development of spontaneous hypertension. Insulin-like growth factor (IGF) I and II exert endocrine and paracrine effects that are required for normal growth and nephron development. We tested the hypothesis that low nephron number is already present during fetal development, and the expression pattern of important molecules of the IGF system is altered in MWF rat during the critical period of kidney development.

METHODS

We compared MWF and normal Wistar rats during nephrogenesis at day 19 of fetal development (E19) and adult rats at postnatal day 100 (D100). Histomorphometric analysis was performed by stereological methods. Quantitative messenger RNA and protein expression was determined by real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

At E19, glomerular density (-32%) and hepatic mRNA (-48%) and protein (-18%) expression of IGF-I were decreased (P < 0.05, respectively), whereas renal mRNA expression of IGF-II receptor (+52%) and IGF binding protein 3 (+113%) were increased in MWF compared with Wistar rats (P < 0.05, respectively). Systolic blood pressure, urinary albumin excretion, and mean glomerular area were significantly elevated in MWF compared with Wistar rats at D100 (P < 0.05, respectively).

CONCLUSIONS

The fetal expression of IGF system molecules in the MWF rat model points towards a link between the decreased availability of active IGF-I and IGF-II and the fetal development of low nephron number, with manifestation of genetic hypertension in adult life.

Update of extracellular matrix, its receptors, and cell adhesion molecules in mammalian nephrogenesis

One of the hallmarks of mammalian nephrogenesis includes a mesenchymal-epithelial transition that is accomplished by intercalation of the ureteric bud, an epithelium-lined tubelike structure, into an undifferentiated mesenchyme, and the latter then undergoes an inductive transformation and differentiates into an epithelial phenotype. At the same time, the differentiating mesenchyme reciprocates by inducing branching morphogenesis of the ureteric bud, which forms a treelike structure with dichotomous iterations. These reciprocal inductive interactions lead to the development of a functioning nephron unit made up of a glomerulus and proximal and distal tubules. The inductive interactions and differentiation events are modulated by a number of transcription factors, protooncogenes, and growth factors and their receptors, which regulate the expression of target morphogenetic modulators including the ECM, integrin receptors, and cell adhesion molecules. These target macromolecules exhibit spatiotemporal and stage-specific developmental regulation in the metanephros. The ECM molecules expressed at the epithelial-mesenchymal interface are perhaps the most relevant and conducive to the paracrine-juxtacrine interactions in a scenario where the ligand is expressed in the mesenchyme while the receptor is located in the ureteric bud epithelium or vice versa. In addition, expression of the target ECM macromolecules is regulated by matrix metalloproteinases and their inhibitors to generate a concentration gradient at the interface to further propel epithelial-mesenchymal interactions so that nephrogenesis can proceed seamlessly. In this review, we discuss and update our current understanding of the role of the ECM and related macromolecules with respect to metanephric development.

Imprinted mesodermal specific transcript (MEST) and H19 genes in renal development and diabetes

BACKGROUND

Imprinted genes, mesodermal specific cDNA or transcript (MEST) and H19, are implicated in peri-implantation embryogenesis, and their expression was assessed in embryonic kidneys undergoing glucose-induced dysmorphogenesis.

METHODS

MEST and H19 mRNA expression was assessed by Northern blot analysis in embryonic kidneys of mice harvested at day 15 to day 19 of gestation and of 1-week-old mice obtained from hyperglycemic mothers. A full-length mouse MEST cDNA was isolated, subcloned into an expression vector, a recombinant protein prepared and an antibody raised; the latter was used to assess protein expression by immunoprecipitation and immunofluorescence microscopy in day 13 metanephric explants subjected to high glucose ambience. Also, MEST mRNA expression was assessed in high d glucose-treated explants by competitive reverse transcription-polymerase chain reaction (RT-PCR) analyses and by in situ tissue autoradiography.

RESULTS

A high expression of MEST and H19 with respective transcript size of approximately 2.7 and approximately 2.4 kb was observed in fetal kidneys, and their expression decreased during the successive stages of gestation and was undetectable in the postnatal period. At day 13, the MEST mRNA was expressed in the mesenchyme, while H19 was expressed in the ureteric bud branches and epithelial elements of the metanephros. Their expression decreased with progression of gestation. By competitive RT-PCR and Northern blot and in situ autoradiographic analyses, both MEST and H19 expressions decreased in day 13 explants treated with high glucose and in the kidneys of fetuses obtained from diabetic mothers. The MEST protein expression was observed in the metanephric epithelial elements and ureteric bud branches instead of in the mesenchyme, and its expression decreased in glucose-treated dysmorphogenetic explants, as assessed by immunofluorescence and immunoprecipitation methods.

CONCLUSION

MEST and H19 imprinted genes are strategically located in the mammalian embryonic metanephros. They are developmentally regulated and their concomitant decreased expression in high glucose ambience or diabetic state did not follow the prevailing dogma of reciprocal inactivation/activation of imprinted genes, and such a decrease may be responsible for the perturbed epithelial:mesenchymal interactions leading to dysmorphogenesis of the mammalian metanephros.

Molecular mechanisms of renal development

The biology of renal development has become increasingly complex because technical advances in genetics and cell biology have been used to study this aspect of embryogenesis. The molecular biology and genetics of renal development may seem inconsequential and frustrating to the practicing clinician, but insight into fundamental mechanisms of renal development are necessary to understand clinical breakthroughs that will occur in the future. As a basis for appreciating these concepts, specific paradigms of renal development are illustrated and the investigative strategies used to develop them are summarized in this article.

Identification of insulin-producing cells derived from embryonic stem cells by zinc-chelating dithizone

BACKGROUND AND AIMS

Embryonic stem (ES) cells have a pluripotent ability to differentiate into a variety of cell lineages in vitro. We have recently identified the emergence of cellular clusters within differentiated ES cell cultures by staining with dithizone (DTZ). DTZ is a zinc-chelating agent known to selectively stain pancreatic beta cells because of their high zinc content. The aim of the present study was to investigate the characteristics of DTZ-stained cellular clusters originating from ES cells.

METHODS

Embryoid bodies (EBs), formed by a 5-day hanging drop culture of ES cells, were allowed to form outgrowths in the culture. The outgrowths were incubated in DTZ solution (final concentration, 100 microg/ml ) for 15 minutes before being examined microscopically. The gene expression of endocrine pancreatic markers was also analyzed by reverse transcriptase-polymerase chain reaction. In addition, insulin production was examined immunohistochemically, and its secretion was examined using enzyme-linked immunosorbent assay.

RESULTS

DTZ-stained cellular clusters appeared after approximately 16 days in the EB culture and became more apparent by day 23. They were found to be immunoreactive to insulin and expressed pancreatic-duodenal homeobox 1 (PDX1), proinsulin 1, proinsulin 2, glucagon, pancreatic polypeptide, glucose transporter-2 (GLUT2), and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) mRNA. They were also able to secrete detectable amounts of insulin.

CONCLUSIONS

ES cell-derived DTZ-positive cellular clusters possess characteristics of the endocrine pancreas, including insulin secretion. Further, DTZ staining is a useful method for the identification of differentiated pancreatic islets developed from EBs in vitro.

Relevance of renal-specific oxidoreductase in tubulogenesis during mammalian nephron development

Renal-specific oxidoreductase (RSOR), an enzyme relevant to diabetic nephropathy, is exclusively expressed in renal tubules. Studies were initiated to determine whether, like other tubule-specific proteins, it selectively modulates tubulogenesis. Northern blot analyses revealed a approximately 1.5-kb transcript, and RSOR expression was detectable in mice embryonic kidneys at day 13, gradually increased by day 17, and extended into neo- and postnatal periods. RSOR mRNA and protein expression was confined to proximal tubules, commencing at gestational day 17 and increasing subsequently, but remained absent in glomeruli and medulla. Treatment with RSOR antisense oligodeoxynucleotide resulted in a dose-dependent dysmorphogenesis of metanephric explants harvested at gestational day 13. The explants were smaller and had expanded mesenchyme, and the population of tubules was markedly decreased. The glomeruli were unaffected, as assessed by mRNA expression of glomerular epithelial protein 1 and reactivity with wheat germ agglutinin. Antisense treatment led to a selective reduction of RSOR mRNA. Immunoprecipitation also indicated a selective translational blockade of RSOR. These findings suggest that RSOR is developmentally regulated, exhibits a distinct spatiotemporal distribution, and probably plays a role in tubulogenesis.

Protein localization and mRNA expression of epimorphin in mouse and human kidneys

Epimorphin is a mesenchymal cell surface protein which induces epithelial branching morphogenesis. However, the role of epimorphin in the kidney has not been addressed. In the present study, the localization of epimorphin protein and the expression of its mRNA were investigated in the developing mouse and adult human kidneys using immunohistochemistry and semiquantitative RT-PCR. The in vitro expression of epimorphin protein and its mRNA was also explored in cultured mouse and human mesangial cells. Epimorphin protein was expressed in the renal interstitium and the circumference of the comma-shaped body at day 16 of gestation. The intensity and distribution of epimorphin were gradually increased during kidney differentiation and maturation. Epimorphin was first observed in glomeruli at 1 week of age. The localization of epimorphin in glomerular mesangial cells and interstitial fibroblasts was confirmed by immunoelectron microscopy of 2-week-old mouse kidneys. The highest mRNA expression of epimorphin was observed at day 16 of gestation, thereafter it diminished with the maturation of the kidney. A similar localization of epimorphin was observed in a normal adult human kidney. Cultured human mesangial cells expressed epimorphin mRNA 150-kD protein. These results suggest that epimorphin may play a role in the development of the kidney and in the differentiation of fibroblast and mesangial cells.

Altered nephrogenesis due to maternal diabetes is associated with increased expression of IGF-II/mannose-6-phosphate receptor in the fetal kidney

We have recently demonstrated that the exposure to hyperglycemia in utero impairs nephrogenesis in rat fetuses (Amri K et al., Diabetes 48:2240-2245, 1999). Diabetic pregnancy is commonly associated with alterations in the IGF system in fetal tissues. It has also been shown that both IGF-I and IGF-II are produced within developing metanephros and promote renal organogenesis. Therefore, we investigated the effect of maternal diabetes on IGFs and their receptors in developing fetal rat kidney. Diabetes was induced in pregnant rats by a single injection of streptozotocin on day 0 of gestation. We measured the amounts of IGF and their receptors, both proteins and mRNAs, in the metanephroi of fetuses issued from diabetic subjects and in age-matched fetuses from control subjects (14-20 days of gestation). IGF-II was produced throughout fetal nephrogenesis, whereas IGF-I protein was not detected, suggesting a critical role of IGF-II in kidney development. Fetal exposure to maternal diabetes caused no change in IGF production in the early stages of nephrogenesis. Similarly, the amounts of IGF-I receptor and insulin receptor were not altered. By contrast, there was an increase in production of IGF-II/mannose-6-phosphate receptor throughout nephrogenesis. Because this receptor plays an essential role in regulating the action of IGF-II, the altered nephrogenesis in fetuses exposed to maternal diabetes may be linked to a decrease in IGF-II bioavailability.

Embryonic renal epithelia: induction, nephrogenesis, and cell differentiation

Embryonic metanephroi, differentiating into the adult kidney, have come to be a generally accepted model system for organogenesis. Nephrogenesis implies a highly controlled series of morphogenetic and differentiation events that starts with reciprocal inductive interactions between two different primordial tissues and leads, in one of two mainstream processes, to the formation of mesenchymal condensations and aggregates. These go through the intricate process of mesenchyme-to-epithelium transition by which epithelial cell polarization is initiated, and they continue to differentiate into the highly specialized epithelial cell populations of the nephron. Each step along the developmental metanephrogenic pathway is initiated and organized by signaling molecules that are locally secreted polypeptides encoded by different gene families and regulated by transcription factors. Nephrogenesis proceeds from the deep to the outer cortex, and it is directed by a second, entirely different developmental process, the ductal branching of the ureteric bud-derived collecting tubule. Both systems, the nephrogenic (mesenchymal) and the ductogenic (ureteric), undergo a repeat series of inductive signaling that serves to organize the architecture and differentiated cell functions in a cascade of developmental gene programs. The aim of this review is to present a coherent picture of principles and mechanisms in embryonic renal epithelia.

Monitoring antisense oligodeoxynucleotide activity in hematopoietic cells

Traditionally, methods designed to impair translation through direct interactions with target messenger RNA (mRNA) have been designated as "antisense" strategies because of their reliance on the formation of reverse complementary (antisense) Watson-Crick base pairs between the targeting oligodeoxynucleotide (ODN) and the mRNA whose function is to be disrupted. Proof of putative "antisense effects," and other mechanistic studies, would be greatly facilitated by the ability to directly demonstrate hybridization between an antisense (AS) ODN and its mRNA target in vivo. In addition, evidence of AS activity by demonstrating reduced levels of RNA or protein or by showing cleaved target molecules would lend proof of the concept. In this article we discuss how AS ODN may be used to down-regulate target gene expression with an emphasis on those targets chosen for our investigations, and we summarize the methods employed for this type of study.

Relevance of extracellular matrix, its receptors, and cell adhesion molecules in mammalian nephrogenesis

Mammalian nephrogenesis begins by the reciprocal interaction of the ureteric bud with the undifferentiated mesenchyme. The mesenchyme differentiates into an epithelial phenotype with the development of the glomerulus and proximal and distal tubules. At the same time, the mesenchyme stimulates the branching morphogenesis of the ureteric bud that differentiates into the collecting ducts. These inductive interactions and differentiation events are modulated by a number of macromolecules, including the extracellular matrix (ECM), integrin receptors, and cell adhesion molecules. Many of these macromolecules exhibit spatiotemporal developmental regulation in the metanephros. Some are expressed in the mesenchyme, whereas others appear in the ureteric bud epithelia. The molecules expressed in the mesenchyme or at the epithelial:mesenchymal interface may serve as ligands while those in the epithelia serve as the receptors. In such a scenario the ligand and the receptor would be ideally suited for epithelial:mesenchymal paracrine/juxtacrine interactions that are also influenced by RGD sequences and Ca2+ binding domains of the ECM proteins and their receptors. This review addresses the role of such interactions in metanephric development.

Immunohistochemical localization of peroxisomal enzymes in developing rat kidney tissues

We studied the developmental changes in the localization of peroxisome-specific enzymes in rat kidney tissues from embryonic Day 16 to postnatal Week 10 by immunoblot analysis and immunohistochemistry, using antibodies for the peroxisomal enzymes catalase, d-amino acid oxidase, l-alpha-hydroxyacid oxidase (isozyme B), and enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional protein. Peroxisomal enzymes were detected in the neonatal kidney by immunoblot analysis and their amount increased with kidney development. By light microscopic immunohistochemistry, they were first localized in a few proximal tubules in the juxtamedullary cortex of 18-day embryos. The distribution of proximal tubules positive for them expanded towards the superficial cortex with development. The full thickness of the cortex became positive for the staining by 14 days after birth. Peroxisomes could be detected by electron microscopy in structurally immature proximal tubules in 18-day embryos. Their size increased and the ultrastructure of subcompartments became clear with continuing development of proximal tubules. These results show that peroxisomal enzymes appear in the immature proximal tubules in the kidney of embryos and that the ultrastructure of the peroxisomes and localization of the peroxisomal enzymes develop along with the maturation of proximal tubules and kidney tissues.

Real time detection of DNA.RNA hybridization in living cells

Demonstrating hybridization between an antisense oligodeoxynucleotide and its mRNA target has proven to be extremely difficult in living cells. To address this fundamental problem in antisense research, we synthesized "molecular beacon" (MB) reporter oligodeoxynucleotides with matched fluorescent donor and acceptor chromophores on their 5' and 3' ends. In the absence of a complementary nucleic acid strand, the MB remains in a stem-loop conformation where fluorescence resonance energy transfer prevents signal emission. On hybridization with a complementary sequence, the stem-loop structure opens increasing the physical distance between the donor and acceptor moieties thereby reducing fluorescence resonance energy transfer and allowing a detectable signal to be emitted when the beacon is excited by light of the appropriate wavelength. Solution hybridization studies revealed that in the presence of a complementary strand targeted MB could yield up to a 60-fold increase in fluorescence intensity in comparison to control MB. By using a fluorescence microscope fitted with UV fluoride lenses, the detection limit of preformed MB/target sequence duplexes microinjected into cells was found to be >/=1 x 10(-1) ag of MB, or approximately 10 molecules of mRNA. On the basis of this exquisite sensitivity, real-time detection of MB/target mRNA hybridization in living cells was attempted by microinjecting MB targeted to the vav protooncogene, or control MB, into K562 human leukemia cells. Within 15 min, confocal microscopy revealed fluorescence in cells injected with targeted, but not control, MB. These studies suggest that real-time visualization and localization of oligonucleotide/mRNA interactions is now possible. MB could find utility in studying RNA processing, trafficking, and folding in living cells. We hypothesize that MB may also prove useful for finding targetable mRNA sequence under physiologic conditions.

Differential effects of Wilms tumor WT1 splice variants on the insulin receptor promoter

The Wilms tumor gene WT1 has been implicated in the early development of the kidney. Mutations in WT1 are found in a small fraction of Wilms tumor, a pediatric nephroblastoma, and Denys-Drash syndrome, characterized by genitourinary abnormalities. The WT1 gene product functions as a transcriptional repressor of growth factor-related genes. The kidney is one of the major sites of insulin action in vivo and expresses high levels of insulin receptors (IR). IR expression has been detected during early embryogenesis, suggesting that it may play a role in development. We investigated whether two WT1 splice variants lacking or including a three-amino-acid (KTS) insertion between the third and fourth zinc finger in the DNA-binding domain could repress the IR promoter in vitro. We show that the +KTS variant effectively represses promoter activity under all conditions tested but the -KTS variant was only able to repress in the presence of cotransfected C/EBP beta or a dominant-negative p53 mutation. Deletional mapping indicated that distinct regions of the IR promoter mediated the effects of the two isoforms and DNaseI footprint analysis identified potential WT1 binding sites within these regions.