Microarray analysis of novel cell lines representing two stages of metanephric mesenchyme differentiation

Reduced nephron endowment in the common Six2-TGC tg mouse line is due to Six3 misexpression by aberrant enhancer-promoter interactions in the transgene

Lifelong kidney function relies on the complement of nephrons generated during mammalian development from a mesenchymal nephron progenitor cell (NPC) population. Low nephron endowment confers increased susceptibility to chronic kidney disease. We asked whether reduced nephron numbers in the popular Six2TGC transgenic mouse line 1 was due to disruption of a regulatory gene at the integration site or to ectopic expression of a gene(s) contained within the transgene. Targeted locus amplification identified integration of the Six2TGC transgene within an intron of Cntnap5a on chr1. We generated Hi-C datasets from NPCs isolated from the Six2TGC tg/+ mice, the Cited1 CreERT2/+ control mice, and the Six2TGC tg/+ ; Tsc1 +/Flox,2 mice that exhibited restored nephron number compared with Six2TGC tg/+ mice, and mapped the precise integration of Six2TGC and Cited1 CreERT2 transgenes to chr1 and chr14, respectively. No changes in topology, accessibility, or expression were observed within the 50-megabase region centered on Cntnap5a in Six2TGC tg/+ mice compared with control mice. By contrast, we identified an aberrant regulatory interaction between a Six2 distal enhancer and the Six3 promoter contained within the transgene. Increasing the Six2TGC tg to Six2 locus ratio or removing one Six2 allele in Six2TGC tg/+ mice, caused severe renal hypoplasia. Furthermore, CRISPR disruption of Six3 within the transgene ( Six2TGC Δ Six3CT ) restored nephron endowment to wildtype levels and abolished the stoichiometric effect. Data from genetic and biochemical studies together suggest that in Six2TGC, SIX3 interferes with SIX2 function in NPC renewal through its C-terminal domain.

Significance

Using high-resolution chromatin conformation and accessibility datasets we mapped the integration site of two popular transgenes used in studies of nephron progenitor cells and kidney development. Aberrant enhancer-promoter interactions drive ectopic expression of Six3 in the Six2TGC tg line which was correlated with disruption of nephrogenesis. Disruption of Six3 within the transgene restored nephron numbers to control levels; further genetic and biochemical studies suggest that Six3 interferes with Six2 -mediated regulation of NPC renewal.

WT1 regulates expression of DNA repair gene Neil3 during nephrogenesis

Mammalian nephrons arise from a population of nephron progenitor cells (NPCs) expressing the master transcription factor Wilms tumor-1 (WT1), which is crucial for NPC proliferation, migration, and differentiation. In humans, biallelic loss of WT1 precludes nephrogenesis and leads to the formation of Wilms tumor precursor lesions. We hypothesize that WT1 normally primes the NPC for nephrogenesis by inducing expression of NPC-specific DNA repair genes that protect the genome. We analyzed transcript levels for a panel of DNA repair genes in embryonic day 17.5 (E17.5) versus adult mouse kidneys and noted seven genes that were increased >20-fold. We then isolated Cited1⁺ NPCs from E17.5 kidneys and found that only one gene, nei-like DNA glycosylase 3 (Neil3), was enriched. RNAscope in situ hybridization of E17.5 mouse kidneys showed increased Neil3 expression in the nephrogenic zone versus mature nephron structures. To determine whether Neil3 expression is WT1 dependent, we knocked down Wt1 in Cited1⁺ NPCs (60% knockdown efficiency) and noted a 58% reduction in Neil3 transcript levels. We showed that WT1 interacts with the Neil3 promoter and that activity of a Neil3 promoter-reporter vector was increased twofold in WT1⁺ versus WT1^- cells. We propose that Neil3 is a WT1-dependent DNA repair gene expressed at high levels in Cited1⁺ NPCs, where it repairs mutational injury to the genome during nephrogenesis. NEIL3 is likely just one of many such lineage-specific repair mechanisms that respond to genomic injury during kidney development.NEW & NOTEWORTHY We studied the molecular events leading to Wilms tumors as a model for the repair of genomic injury. Specifically, we showed that WT1 activates DNA repair gene Neil3 in nephron progenitor cells. However, our observations offer a much broader principle, demonstrating that the embryonic kidney invests in lineage-specific expression of DNA repair enzymes. Thus, it is conceivable that failure of these mechanisms could lead to a variety of "sporadic" congenital renal malformations and human disease.

Temporally and spatially regulated collagen XVIII isoforms are involved in ureteric tree development via the TSP1-like domain

Collagen XVIII (ColXVIII) is a component of the extracellular matrix implicated in embryogenesis and control of tissue homoeostasis. We now provide evidence that ColXVIII has a specific role in renal branching morphogenesis as observed in analyses of total and isoform-specific knockout embryos and mice. The expression of the short and the two longer isoforms differ temporally and spatially during renal development. The lack of ColXVIII or its specific isoforms lead to congenital defects in the 3D patterning of the ureteric tree where the short isoform plays a prominent role. Moreover, the ex vivo data suggests that ColXVIII is involved in the kidney epithelial tree patterning via its N-terminal domains, and especially the Thrombospondin-1-like domain common to all isoforms. This morphogenetic function likely involves integrins expressed in the ureteric epithelium. Altogether, the results point to an important role for ColXVIII in the matrix-integrin-mediated functions regulating renal development.

Magnetic resonance urography of congenital abnormalities - what the radiologist needs to know

Congenital abnormalities of the kidney and urinary tract include a wide range of malformations ranging from asymptomatic to life-threatening conditions. Although pediatric urogenital system imaging is based on the use of US (pre- and postnatal), voiding cystourethrography and scintigraphic study, magnetic resonance (MR) urography plays a fundamental role in the classification and management of congenital abnormalities of the kidney and urinary tract, giving an overview of the different clinical pictures, thanks to its panoramicity and high anatomical detail. In fact the anomalies of the urinary tract are phenotypically variable because they can affect simultaneously several segments of different embryonic derivation, with complex clinical pictures; they can appear both as isolated phenotypes or as complex malformative conditions, involving renal parenchyma, collecting system and bladder. A deep knowledge of this complex embryogenesis and its possible phenotypic patterns allows a correct interpretation of MR urography images. We describe the embryology and pathophysiology of congenital abnormalities of the kidney and urinary tract as well as MR urography technique and findings. Congenital abnormalities of the kidney and urinary tract are classified into four groups: (1) obstruction (proximal, middle and distal), (2) budding with respect to the Wolffian duct (site and number of ureter), (3) ascent and rotation (ectopia, malrotation and fusion of kidney) and (4) anomaly of metanephric differentiation (dysplasia, megapolicalycosis).

Runx1 shapes the chromatin landscape via a cascade of direct and indirect targets

Runt-related transcription factor 1 (Runx1) can act as both an activator and a repressor. Here we show that CRISPR-mediated deletion of Runx1 in mouse metanephric mesenchyme-derived mK4 cells results in large-scale genome-wide changes to chromatin accessibility and gene expression. Open chromatin regions near down-regulated loci enriched for Runx sites in mK4 cells lose chromatin accessibility in Runx1 knockout cells, despite remaining Runx2-bound. Unexpectedly, regions near upregulated genes are depleted of Runx sites and are instead enriched for Zeb transcription factor binding sites. Re-expressing Zeb2 in Runx1 knockout cells restores suppression, and CRISPR mediated deletion of Zeb1 and Zeb2 phenocopies the gained expression and chromatin accessibility changes seen in Runx1KO due in part to subsequent activation of factors like Grhl2. These data confirm that Runx1 activity is uniquely needed to maintain open chromatin at many loci, and demonstrate that Zeb proteins are required and sufficient to maintain Runx1-dependent genome-scale repression.

Runt-related transcription factor (Runx) 1 & 2 impact development and disease by activating or repressing transcription. In this manuscript we used genome editing tools to remove Runx1, and as expected, observed widespread changes in chromatin accessibility. Newly closed areas contained Runx1 binding sites and were enriched near genes whose expression depended on Runx1. Interestingly, this occurred despite continued binding of Runx2 to the same regions of DNA, which suggests that Runx2 is insufficient to maintain open chromatin and expression of Runx1 target genes in this cellular context. By contrast, newly opened chromatin regions, many near genes that were upregulated in Runx1 knockout cells, did not enrich for Runx1 binding sites. Instead, these regions were enriched for sites for the repressor Zeb proteins. We found that the loss of Zeb 1 & 2 expression, direct transcriptional targets of Runx1, resulted in the opening of chromatin and upregulation of genes residing near the newly open sites in Runx1 knockout cells. The same sites were also open and nearby genes expressed in edited Zeb1 and Zeb2 knockout cells. Among them were transcription factors, such as the Grhl2 gene, which in turn bind to and upregulate their target genes. Thus, the loss of a single transcription factor initiates a cascade of direct and indirect ramifications with likely negative effects on development and health.

Notch dimerization and gene dosage are important for normal heart development, intestinal stem cell maintenance, and splenic marginal zone B-cell homeostasis during mite infestation

Cooperative DNA binding is a key feature of transcriptional regulation. Here we examined the role of cooperativity in Notch signaling by CRISPR-mediated engineering of mice in which neither Notch1 nor Notch2 can homo- or heterodimerize, essential for cooperative binding to sequence-paired sites (SPS) located near many Notch-regulated genes. Although most known Notch-dependent phenotypes were unaffected in Notch1/2 dimer-deficient mice, a subset of tissues proved highly sensitive to loss of cooperativity. These phenotypes include heart development, compromised viability in combination with low gene dose, and the gut, developing ulcerative colitis in response to 1% dextran sulfate sodium (DSS). The most striking phenotypes-gender imbalance and splenic marginal zone B-cell lymphoma-emerged in combination with gene dose reduction or when challenged by chronic fur mite infestation. This study highlights the role of the environment in malignancy and colitis and is consistent with Notch-dependent anti-parasite immune responses being compromised in Notch dimer-deficient animals.

Physical interactions between Gsx2 and Ascl1 balance progenitor expansion versus neurogenesis in the mouse lateral ganglionic eminence

The Gsx2 homeodomain transcription factor promotes neural progenitor identity in the lateral ganglionic eminence (LGE), despite upregulating the neurogenic factor Ascl1. How this balance in maturation is maintained is unclear. Here, we show that Gsx2 and Ascl1 are co-expressed in subapical progenitors that have unique transcriptional signatures in LGE ventricular zone (VZ) cells. Moreover, whereas Ascl1 misexpression promotes neurogenesis in dorsal telencephalic progenitors, the co-expression of Gsx2 with Ascl1 inhibits neurogenesis. Using luciferase assays, we found that Gsx2 reduces the ability of Ascl1 to activate gene expression in a dose-dependent and DNA binding-independent manner. Furthermore, Gsx2 physically interacts with the basic helix-loop-helix (bHLH) domain of Ascl1, and DNA-binding assays demonstrated that this interaction interferes with the ability of Ascl1 to bind DNA. Finally, we modified a proximity ligation assay for tissue sections and found that Ascl1-Gsx2 interactions are enriched within LGE VZ progenitors, whereas Ascl1-Tcf3 (E-protein) interactions predominate in the subventricular zone. Thus, Gsx2 contributes to the balance between progenitor maintenance and neurogenesis by physically interacting with Ascl1, interfering with its DNA binding and limiting neurogenesis within LGE progenitors.

The Initiation of Meiotic Sex Chromosome Inactivation Sequesters DNA Damage Signaling from Autosomes in Mouse Spermatogenesis

Meiotic sex chromosome inactivation (MSCI) is an essential event in the mammalian male germline. MSCI is directed by a DNA damage response (DDR) pathway centered on the phosphorylation of histone variant H2AX at serine 139 (termed γH2AX). The failure to initiate MSCI is linked to complete meiotic arrest and elimination of germ cells; however, the mechanisms underlying this arrest and elimination remain unknown. To address this question, we established a new separation-of-function mouse model for H2ax that shows specific and complete defects in MSCI. The genetic change is a point mutation in which another H2AX amino acid residue important in the DDR, tyrosine 142 (Y142), is converted to alanine (H2ax-Y142A). In H2ax-Y142A meiosis, the establishment of DDR signals on the chromosome-wide domain of the sex chromosomes is impaired. The initiation of MSCI is required for stage progression, which enables crossover formation, suggesting that the establishment of MSCI permits the timely progression of male meiosis. Our results suggest that normal meiotic progression requires the removal of ATR-mediated DDR signaling from autosomes. We propose a novel biological function for MSCI: the initiation of MSCI sequesters DDR factors from autosomes to the sex chromosomes at the onset of the pachytene stage, and the subsequent formation of an isolated XY nuclear compartment-the XY body-sequesters DDR factors to permit meiotic progression from the mid-pachytene stage onward. VIDEO ABSTRACT.

Hedgehog Interacting Protein Promotes Fibrosis and Apoptosis in Glomerular Endothelial Cells in Murine Diabetes

We investigated whether renal hedgehog interacting protein (Hhip) expression contributes to the progression of diabetic nephropathy (DN) and studied its related mechanism(s) in vivo and in vitro. Here, we show that Hhip expression is highly elevated in glomerular endothelial cells of adult type 1 diabetic (T1D) Akita and T2D db/db mouse kidneys as compared to non-diabetic control littermates. Hyperglycemia enhances reactive oxygen species (ROS) generation via NADPH oxidase 4 (Nox4) activation and stimulates renal Hhip gene expression, and that elevated renal Hhip gene expression subsequently activates the TGFβ1- Smad2/3 cascade and promotes endothelial to mesenchymal transition associated with endothelial cell fibrosis/apoptosis in vivo and in vitro. Furthermore, kidneys of low-dose streptozotocin-induced diabetic heterozygous Hhip deficient (Hhip^+/−) mice displayed a normal albumin/creatinine ratio with fewer features of DN (glomerulosclerosis/fibrosis and podocyte apoptosis/loss) and less evidence of renal compensation (glomerular hypertrophy and hyperfiltration) as compared to diabetic wild type controls (Hhip^+/+). Thus, our studies demonstrated that renal Hhip expression is associated with nephropathy development in diabetes and that hyperglycemia-induced renal Hhip expression may mediate glomerular endothelial fibrosis and apoptosis in diabetes, a novel finding.

TβRII Regulates the Proliferation of Metanephric Mesenchyme Cells through Six2 In Vitro

The transforming growth factor-β (TGFβ) family signaling pathways play an important role in regulatory cellular networks and exert specific effects on developmental programs during embryo development. However, the function of TGFβ signaling pathways on the early kidney development remains unclear. In this work, we aim to detect the underlying role of TGFβ type II receptor (TβRII) in vitro, which has a similar expression pattern as the crucial regulator Six2 during early kidney development. Firstly, the 5-ethynyl-2′-deoxyuridine (EdU) assay showed knock down of TβRII significantly decreased the proliferation ratio of metanephric mesenchyme (MM) cells. Additionally, real-time Polymerase Chain Reaction (PCR) and Western blot together with immunofluorescence determined that the mRNA and protein levels of Six2 declined after TβRII knock down. Also, Six2 was observed to be able to partially rescue the proliferation phenotype caused by the depletion of TβRII. Moreover, bioinformatics analysis and luciferase assay indicated Smad3 could transcriptionally target Six2. Further, the EdU assay showed that Smad3 could also rescue the inhibition of proliferation caused by the knock down of TβRII. Taken together, these findings delineate the important function of the TGFβ signaling pathway in the early development of kidney and TβRII was shown to be able to promote the expression of Six2 through Smad3 mediating transcriptional regulation and in turn activate the proliferation of MM cells.

Six2 Is a Coordinator of LiCl-Induced Cell Proliferation and Apoptosis

The metanephric mesenchyme (MM) cells are a subset of kidney progenitor cells and play an essential role in mesenchymal-epithelial transition (MET), the key step of nephron generation. Six2, a biological marker related to Wnt signaling pathway, promotes the proliferation, inhibits the apoptosis and maintains the un-differentiation of MM cells. Besides, LiCl is an activator of Wnt signaling pathway. However, the role of LiCl in cellular regulation of MM cells remains unclear, and the relationship between LiCl and Six2 in this process is also little known. Here, we performed EdU assay and flow cytometry assay to, respectively, detect the proliferation and apoptosis of MM cells treated with LiCl of increasing dosages. In addition, reverse transcription-PCR (RT-PCR) and Western-blot were conducted to measure the expression of Six2 and some maker genes of Wnt and bone-morphogenetic-protein (BMP) signaling pathway. Furthermore, luciferase assay was also carried out to detect the transcriptional regulation of Six2. Then we found LiCl promoted MM cell proliferation at low-concentration (10, 20, 30, and 40 mM). The expression of Six2 was dose-dependently increased in low-concentration (10, 20, 30, and 40 mM) at both mRNA and protein level. In addition, both of cell proliferation and Six2 expression in MM cells declined when dosage reached high-concentration (50 mM). However, Six2 knock-down converted the proliferation reduction at 50 mM. Furthermore, Six2 deficiency increased the apoptosis of MM cells, compared with negative control cells at relative LiCl concentration. However, the abnormal rise of apoptosis at 30 mM of LiCl concentration implies that it might be the reduction of GSK3β that increased cell apoptosis. Together, these demonstrate that LiCl can induce the proliferation and apoptosis of MM cells coordinating with Six2.

Golgb1 regulates protein glycosylation and is crucial for mammalian palate development

Cleft palate is a common major birth defect for which currently known causes account for less than 30% of pathology in humans. In this study, we carried out mutagenesis screening in mice to identify new regulators of palatogenesis. Through genetic linkage mapping and whole-exome sequencing, we identified a loss-of-function mutation in the Golgb1 gene that co-segregated with cleft palate in a new mutant mouse line. Golgb1 is a ubiquitously expressed large coiled-coil protein, also known as giantin, that is localized at the Golgi membrane. Using CRISPR/Cas9-mediated genome editing, we generated and analyzed developmental defects in mice carrying additional Golgb1 loss-of-function mutations, which supported a crucial requirement for Golgb1 in palate development. Through maxillary explant culture assays, we demonstrate that the Golgb1 mutant embryos have intrinsic defects in palatal shelf elevation. Just prior to the developmental stage of palatal shelf elevation in wild-type littermates, Golgb1 mutant embryos exhibit increased cell density, reduced hyaluronan accumulation and impaired protein glycosylation in the palatal mesenchyme. Together, these results demonstrate that, although it is a ubiquitously expressed Golgi-associated protein, Golgb1 has specific functions in protein glycosylation and tissue morphogenesis.

SpDamID: Marking DNA Bound by Protein Complexes Identifies Notch-Dimer Responsive Enhancers

We developed Split DamID (SpDamID), a protein complementation version of DamID, to mark genomic DNA bound in vivo by interacting or juxtapositioned transcription factors. Inactive halves of DAM (DNA adenine methyltransferase) were fused to protein pairs to be queried. Either direct interaction between proteins or proximity enabled DAM reconstitution and methylation of adenine in GATC. Inducible SpDamID was used to analyze Notch-mediated transcriptional activation. We demonstrate that Notch complexes label RBP sites broadly across the genome and show that a subset of these complexes that recruit MAML and p300 undergo changes in chromatin accessibility in response to Notch signaling. SpDamID differentiates between monomeric and dimeric binding, thereby allowing for identification of half-site motifs used by Notch dimers. Motif enrichment of Notch enhancers coupled with SpDamID reveals co-targeting of regulatory sequences by Notch and Runx1. SpDamID represents a sensitive and powerful tool that enables dynamic analysis of combinatorial protein-DNA transactions at a genome-wide level.

MiR-181b targets Six2 and inhibits the proliferation of metanephric mesenchymal cells in vitro

MicroRNAs (miRNAs) are small non-coding RNAs that down-regulate gene expression by binding to target mRNA for cleavage or translational repression, and play important regulatory roles in renal development. Despite increasing genes have been predicted to be miRNA targets by bioinformatic analysis during kidney development, few of them have been verified by experiment. The objective of our study is to identify the miRNAs targeting Six2, a critical transcription factor that maintains the mesenchymal progenitor pool via self-renewal (proliferation) during renal development. We initially analyzed the 3'UTR of Six2 and found 37 binding sites targeted by 50 putative miRNAs in the 3'UTR of Six2. Among the 50 miRNAs, miR-181b is the miRNAs predicted by the three used websites. In our study, the results of luciferase reporter assay, realtime-PCR and Western blot demonstrated that miR-181b directly targeted on the 3'UTR of Six2 and down-regulate the expression of Six2 at mRNA and protein levels. Furthermore, EdU proliferation assay along with the Six2 rescue strategy showed that miR-181b suppresses the proliferation of metanephric mesenchymal by targeting Six2 in part. In our research, we concluded that by targeting the transcription factor gene Six2, miR-181b inhibits the proliferation of metanephric mesenchymal cells in vitro and might play an important role in the formation of nephrons.

Histone signature of metanephric mesenchyme cell lines

The metanephric mesenchyme (MM) gives rise to nephrons, the filtering units of the mature kidney. The MM is composed of uninduced (Six2(high)/Lhx1(low)) and induced (Wnt-stimulated, Six2(low)/Lhx1(high)) cells. The global epigenetic state of MM cells is unknown, partly due to technical difficulty in isolating sufficient numbers of homogenous cell populations. We therefore took advantage of two mouse clonal cell lines representing the uninduced (mK3) and induced (mK4) metanephric mesenchyme (based on gene expression profiles and ability to induce branching of ureteric bud). ChIP-Seq revealed that whereas H3K4me3 active region "peaks" are enriched in metabolic genes, H3K27me3 peaks decorate mesenchyme and epithelial cell fate commitment genes. In uninduced mK3 cells, promoters of "stemness" genes (e.g., Six2, Osr1) are enriched with H3K4me3 peaks; these are lost in induced mK4 cells. ChIP-qPCR confirmed this finding and further demonstrated that G9a/H3K9me2 occupy the promoter region of Six2 in induced cells, consistent with the inactive state of transcription. Conversely, genes that mark the induced epithelialized state (e.g., Lhx1, Pax8), transition from a non-permissive to an active chromatin signature in mK3 vs. mK4 cells, respectively. Importantly, stimulation of Wnt signaling in uninduced mK3 cells provokes an active chromatin state (high H3K4me3, low H3K27me3), recruitment of β-catenin, and loss of pre-bound histone methyltransferase Ezh2 in silent induced genes followed by activation of transcription. We conclude that the chromatin signature of uninduced and induced cells correlates strongly with their gene expression states, suggesting a role of chromatin-based mechanisms in MM cell fate.

Shaping segments: Hox gene function in the genomic age

Despite decades of research, morphogenesis along the various body axes remains one of the major mysteries in developmental biology. A milestone in the field was the realisation that a set of closely related regulators, called Hox genes, specifies the identity of body segments along the anterior-posterior (AP) axis in most animals. Hox genes have been highly conserved throughout metazoan evolution and code for homeodomain-containing transcription factors. Thus, they exert their function mainly through activation or repression of downstream genes. However, while much is known about Hox gene structure and molecular function, only a few target genes have been identified and studied in detail. Our knowledge of Hox downstream genes is therefore far from complete and consequently Hox-controlled morphogenesis is still poorly understood. Genome-wide approaches have facilitated the identification of large numbers of Hox downstream genes both in Drosophila and vertebrates, and represent a crucial step towards a comprehensive understanding of how Hox proteins drive morphological diversification. In this review, we focus on the role of Hox genes in shaping segmental morphologies along the AP axis in Drosophila, discuss some of the conclusions drawn from analyses of large target gene sets and highlight methods that could be used to gain a more thorough understanding of Hox molecular function. In addition, the mechanisms of Hox target gene regulation are considered with special emphasis on recent findings and their implications for Hox protein specificity in the context of the whole organism.

Gene expression profiles in developing nephrons using Lim1 metanephric mesenchyme-specific conditional mutant mice

BACKGROUND

Lim1 is a homeobox gene that is essential for nephrogenesis. During metanephric kidney development, Lim1 is expressed in the nephric duct, ureteric buds, and the induced metanephric mesenchyme. Conditional ablation of Lim1 in the metanephric mesenchyme blocks the formation of nephrons at the nephric vesicle stage, leading to the production of small, non-functional kidneys that lack nephrons.

METHODS

In the present study, we used Affymetrix probe arrays to screen for nephron-specific genes by comparing the expression profiles of control and Lim1 conditional mutant kidneys. Kidneys from two developmental stages, embryonic day 14.5 (E14.5) and 18.5 (E18.5), were examined.

RESULTS

Comparison of E18.5 kidney expression profiles generated a list of 465 nephron-specific gene candidates that showed a more than 2-fold increase in their expression level in control kidney versus the Lim1 conditional mutant kidney. Computational analysis confirmed that this screen enriched for kidney-specific genes. Furthermore, at least twenty-eight of the top fifty (56%) candidates (or their vertebrate orthologs) were previously reported to have a nephron-specific expression pattern. Our analysis of E14.5 expression data yielded 41 candidate genes that are up-regulated in the control kidneys compared to the conditional mutants. Three of them are related to the Notch signaling pathway that is known to be important in cell fate determination and nephron patterning.

CONCLUSION

Therefore, we demonstrate that Lim1 conditional mutant kidneys serve as a novel tissue source for comprehensive expression studies and provide a means to identify nephron-specific genes.

Changes in gene expression profiles induced by parvovirus H-1 in human gastric cancer cells

OBJECTIVE

The autonomous parvovirus H-1 exhibits preferential toxicity for transformed or tumor cells. The precise molecular mechanism of H-1 virus-associated cytotoxicity is not fully understood. The present study aimed at gaining more information about parvovirus-induced cellular disturbances.

METHODS

The H-1 virus-sensitive human gastric cancer cell line HGC27 was analyzed in the present study. cDNA microarrays were used to determine the global cellular gene expression changes which occur during the process of H-1 virus-induced death of HGC27 cells. A subset of differential expressed genes was further tested by RT-PCR and Northern blot analyzes.

RESULTS

A total of 920 genes belonging to various functional groups were found to be differentially expressed in H-1 virus- versus mock-infected cells in cDNA microarrays. Among them, 363 genes were upregulated, whilst 557 genes were downregulated. The differential expressions of some of these genes were further confirmed by RT-PCR and Northern blot analysis.

CONCLUSION

Some of genes known to be involved in cell signal transduction, apoptosis, DNA replication, DNA repair, DNA binding and transcription were differentially expressed after parvovirus H-1 infection, they might play a role in H-1 virus-induced gastric cancer cell death. These genes represent interesting candidates to be tested at the functional level for their contribution to the disturbances triggered by H-1 virus in tumor cells.

Slc12a2 is a direct target of two closely related homeobox proteins, Six1 and Six4

Six genes are homologs of Drosophila sine oculis and encode transcription factors that are characterized by a conserved Six domain and homeodomain. Of the six family members (Six1-Six6) in mice, Six1 and Six4 show similar expression patterns during embryogenesis. Six1-/- mice show defective formation of various organs such as inner ear, nose, skeletal muscle, kidney and thymus, whereas Six4-/- mice show little anomaly in organogenesis. To understand the molecular basis for the differential function of Six1 and Six4 in vivo, we screened target genes of Six1 and Six4 and found that Six1 and Six4 differentially regulated a set of target genes. Gel-retardation assays indicated that the promoter region of one of the targets, sodium-potassium-chloride cotransporter 1 (Slc12a2), contains multiple Six1-binding sites and one common binding site of Six1 and Six4, suggesting that the DNA-binding specificity of Six1 is distinct from that of Six4. This underlies the differential regulation of common target genes by Six1 and Six4. Furthermore, in situ hybridization demonstrated that the expression of Slc12a2 was reduced in the developing dorsal root ganglia of Six1-/-/Six4-/- mice, suggesting that Six1 and Six4 regulate Slc12a2 in vivo.

Conditionally immortalized cell line of inducible metanephric mesenchyme

BACKGROUND

The mesenchymal-epithelial conversion of metanephric mesenchyme (MM) in the formation of nephronic tubules has long served as a paradigm for inductive signaling in morphogenesis. However, the mechanisms underlying this differentiation have remained an enigma due to insufficient numbers of primary mesenchymal cells that must be isolated manually from animal embryos. To overcome this problem, we have established a conditionally immortalized cell line, the rat-inducible metanephric mesenchyme (RIMM-18) by transfection of primary mesenchymal cells with a vector, encoding an estradiol-dependent E1A-ER fusion protein.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), luciferase reporter assay, electrophoretic mobility shift assay, immunocytochemical, and immunohistochemical stainings were used to characterize the established cell line.

RESULTS

We demonstrate that in the presence of estradiol, the RIMM-18 cell line proliferates continuously, maintaining mesenchymal characteristics for over 40 passages. These cells are vimentin-positive and cytokeratin-negative. Under inductive conditions in the absence of estradiol, they are responsive to a number of cytokines, which are established inducers of mesenchymal cells in vivo and in vitro [i.e., fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), and transforming growth factor-beta 2 (TGF-beta 2)]. We show the presence in RIMM-18 cells of specific protein markers and functionally active signaling pathways required for induction of tubule formation in MM. Furthermore, induced RIMM-18 cells change morphology, acquiring epithelial-like features, and begin to express epithelial markers (e.g., E-cadherin, cytokeratin, gamma-glutamyl-transpeptidase, and secreted frizzled-related protein 2 (sFRP2).

CONCLUSION

This preliminary characterization of the RIMM-18 cell line suggests that it will be useful in the study of biochemical and molecular mechanisms of nephronic development and, possibly, of some types of renal cancer such as Wilms' tumor, which caricatures the normal process of kidney development.

Differentiative potential of human metanephric mesenchymal cells

OBJECTIVE

To evaluate the ability of mesenchymal cells derived from nonhematopoietic organs to form blood and other tissues in vitro and in vivo.

MATERIALS AND METHODS

Because of its mesodermic derivation, human fetal kidney was used as a source of mesenchymal cells. Two populations of kidney cells were studied at a nonclonal level: a crude preparation, and an adherent fraction that was derived from the first by propagation in vitro (MNMC). Both populations were transplanted into sheep fetuses and analyzed at intervals for the presence of human cells in different organs by flow cytometry, PCR, immunohistochemistry, and in situ hybridization. Secondary transplantation studies were performed using human hematopoietic cells obtained from the bone marrow (BM) of primary recipients.

RESULTS

MNMC were Thy-1(+), CD51(+), CD44(+), CD45(-), and vimentin(+), a phenotype consistent with that of metanephric mesenchyme. The crude population displayed the same phenotype but was contaminated with 0.4% CD34(+)CD45(+) cells. Cells with hepatocyte-like morphology and phenotype were obtained from the MNMC after culture in specific inducing media. After transplantation, both populations of cells produced multilineage hematopoietic engraftment and gave rise to CD34(+) cells. Successful hematopoietic engraftment in secondary recipients demonstrated the generation of long-term engrafting hematopoietic stem cells from MNMC. PCR analysis confirmed human hematopoietic engraftment and revealed that human cells were also present within other organs. Liver sections of transplanted animals contained human albumin-producing hepatocyte-like cells.

CONCLUSION

A human metanephric mesenchymal cell population simultaneously gave rise to human blood and liver-like cells, suggesting that mesenchymal cells may represent a broad population of putative stem cells in multiple adult organs.

Hoxa 11 is upstream of Integrin alpha8 expression in the developing kidney

Mutation of the functionally redundant Hoxa 11/Hoxd 11 genes gives absent or rudimentary kidneys resulting from a dramatic reduction of the growth and branching of the ureteric bud. To understand better the molecular mechanisms of Hoxa 11/Hoxd 11 function in kidney development, it is necessary to identify the downstream target genes regulated by their encoded transcription factors. To this end, we conducted a screen for Hoxa 11-responsive genes in two kidney cell lines. HEK293 cells, which usually do not express Hoxa 11, were modified to allow inducible Hoxa 11 expression. The mK10 cells, derived specifically for this study from Hoxa 11/Hoxd 11 double-mutant mice, were also modified to give cell populations with and without Hoxa 11 expression. Differential display, Gene Discovery Arrays, and Affymetrix genechip probe arrays were used to screen for genes up- or down-regulated by Hoxa 11. Nine genes, PDGF A, Cathepsin L, annexin A1, Mm.112139, Est2 repressor factor, NrCAM, ZNF192, integrin-associated protein, and GCM1, showed reproducible 3-fold or smaller changes in gene expression in response to Hoxa 11. One gene, the Integrin alpha8, was up-regulated approximately 20-fold after Hoxa 11 expression. The Integrin alpha8 gene is expressed together with Hoxa 11 in metanephric mesenchyme cells, and mutation of Integrin alpha8 gives a bud-branching morphogenesis defect very similar to that observed in Hoxa 11/Hoxd 11 mutant mice. In situ hybridizations showed a dramatic regional reduction in Integrin alpha8 expression in the developing kidneys of Hoxa 11/Hoxd 11 mutant mice. This work suggests that the Integrin alpha8 gene may be a major effector of Hoxa 11/Hoxd 11 function in the developing kidney.