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Developmental Biology Aug 2002In the vertebrate embryo, development of the excretory system is characterized by the successive formation of three distinct kidneys: the pronephros, mesonephros, and...
In the vertebrate embryo, development of the excretory system is characterized by the successive formation of three distinct kidneys: the pronephros, mesonephros, and metanephros. While tubulogenesis in the metanephric kidney is critically dependent on the signaling molecule Wnt-4, it is unknown whether Wnt signaling is equally required for the formation of renal epithelia in the other embryonic kidney forms. We therefore investigated the expression of Wnt genes during the pronephric kidney development in Xenopus. Wnt4 was found to be associated with developing pronephric tubules, but was absent from the pronephric duct. Onset of pronephric Wnt-4 expression coincided with mesenchyme-to-epithelium transformation. To investigate Wnt-4 gene function, we performed gain- and loss-of-function experiments. Misexpression of Wnt4 in the intermediate and lateral mesoderm caused abnormal morphogenesis of the pronephric tubules, but was not sufficient to initiate ectopic tubule formation. We used a morpholino antisense oligonucleotide-based gene knockdown strategy to disrupt Wnt-4 gene function. Xenopus embryos injected with antisense Wnt-4 morpholinos developed normally, but marker gene and morphological analysis revealed a complete absence of pronephric tubules. Pronephric duct development was largely unaffected, indicating that ductogenesis may occur normally in the absence of pronephric tubules. Our results show that, as in the metanephric kidney, Wnt-4 is critically required for tubulogenesis in the pronephric kidney, indicating that a common, evolutionary conserved gene regulatory network may control tubulogenesis in different vertebrate excretory organs.
Topics: Animals; Cell-Free System; Down-Regulation; In Situ Hybridization; Kidney; Mesoderm; Oligonucleotides; Oligonucleotides, Antisense; Phenotype; Plasmids; Protein Biosynthesis; Proto-Oncogene Proteins; RNA, Messenger; Signal Transduction; Transcription, Genetic; Wnt Proteins; Wnt4 Protein; Xenopus; Xenopus Proteins
PubMed: 12142017
DOI: 10.1006/dbio.2002.0712 -
Biochimie Dec 2011From the formation of a simple kidney in amphibian larvae, the pronephros, to the formation of the more complex mammalian kidney, the metanephros, calcium is present... (Review)
Review
From the formation of a simple kidney in amphibian larvae, the pronephros, to the formation of the more complex mammalian kidney, the metanephros, calcium is present through numerous steps of tubulogenesis and nephron induction. Several calcium-binding proteins such as regucalcin/SMP-30 and calbindin-D28k are commonly used to label pronephric tubules and metanephric ureteral epithelium, respectively. However, the involvement of calcium and calcium signalling at various stages of renal organogenesis was not clearly delineated. In recent years, several studies have pinpointed an unsuspected role of calcium in determination of the pronephric territory and for conversion of metanephric mesenchyme into nephrons. Influx of calcium and calcium transients have been recorded in the pool of renal progenitors to allow tubule formation, highlighting the occurrence of calcium-dependent signalling events during early kidney development. Characterization of nuclear calcium signalling is emerging. Implication of the non-canonical calcium/NFAT Wnt signalling pathway as an essential mechanism to promote nephrogenesis has recently been demonstrated. This review examines the current knowledge of the impact of calcium ions during embryonic development of the kidney. It focuses on Ca(2+) binding proteins and Ca(2+) sensors that are involved in renal organogenesis and briefly examines the link between calcium-dependent signals and polycystins.
Topics: Animals; Calcineurin; Calcium; Calcium Signaling; Embryonic Development; Humans; Kidney; NFATC Transcription Factors; Nephrons; TRPP Cation Channels
PubMed: 21802484
DOI: 10.1016/j.biochi.2011.07.007 -
Mechanisms of Development 2010Retinoic acid (RA) signaling is important for the early steps of nephrogenic cell fate specification. Here, we report a novel target gene of RA signaling named XPteg...
Retinoic acid (RA) signaling is important for the early steps of nephrogenic cell fate specification. Here, we report a novel target gene of RA signaling named XPteg (Xenopus proximal tubules-expressed gene) which is critical for pronephric development. XPteg starts to be expressed at the earliest stage of embryonic kidney specification and was restricted to the pronephric proximal tubules during kidney development. Anti-sense morpholino (MO)-mediated knockdown of XPteg perturbed formation of pronephros as demonstrated by reduced expression of pronephric tubule markers. Conversely, overexpression of XPteg promoted endogenous and ectopic expression of those markers and expanded pronephric tubules. Treatment of retinoic acid induced the expression of XPteg in the pronephric field without protein synthesis. Furthermore, we found that the pronephric defects caused by a dominant negative RA receptor could be rescued by coexpression of XPteg. Taken together, these results suggest that XPteg functions as a direct transcriptional target of RA signaling to regulate pronephric tubulogenesis in Xenopus early development.
Topics: Amino Acid Sequence; Animals; Gene Expression Regulation, Developmental; Homeodomain Proteins; In Situ Hybridization; Intracellular Signaling Peptides and Proteins; Kidney Tubules; LIM-Homeodomain Proteins; Membrane Proteins; Mesoderm; Molecular Sequence Data; Nephrons; Oligonucleotides, Antisense; PAX8 Transcription Factor; Paired Box Transcription Factors; Protein Structure, Tertiary; Sequence Homology, Amino Acid; Transcription Factors; Tretinoin; Xenopus Proteins; Xenopus laevis
PubMed: 19909807
DOI: 10.1016/j.mod.2009.11.001 -
RNA Biology 2010Kidney development is a paradigm of how multiple cell types are integrated into highly specialized epithelial structures via various inductive events. A network of... (Review)
Review
Kidney development is a paradigm of how multiple cell types are integrated into highly specialized epithelial structures via various inductive events. A network of transcription factors and signaling pathways have been identified as crucial regulators. The recent discovery of a group of small, non-coding RNAs, microRNAs (miRNAs), has added a new layer of complexity. Studies using the pronephric kidney of Xenopus and the metanephric kidney of mouse have demonstrated that a tight regulation of mRNA stability and translation efficiency by miRNAs is very important as well. The interplay between miRNAs and the transcriptional network provides plasticity and robustness to the system. Importantly, miRNAs are not only necessary for early aspects of kidney development, but also later in life. As such they may provide a mean to maintain/modulate kidney function during homeostasis and injury.
Topics: Animals; Anura; Embryo, Nonmammalian; Humans; Kidney; Mice; MicroRNAs; Models, Animal; Models, Biological; Xenopus
PubMed: 20458188
DOI: 10.4161/rna.7.3.11692 -
Scanning Electron Microscopy 1984It is possible to distinguish differences in pronephric duct morphogenesis by using scanning electron microscopy to observe the results of blocking, marking and grafting... (Comparative Study)
Comparative Study
It is possible to distinguish differences in pronephric duct morphogenesis by using scanning electron microscopy to observe the results of blocking, marking and grafting experiments as well as the normal course of development. Here we compare the mode of pronephric duct development in embryos representing three orders of vertebrates: birds (class, Aves; order, Gallus); frogs (class, Amphibia; order, Anura); and salamanders (class, Amphibia; order, Urodela). The axolotl (a urodele) pronephric duct is formed by the caudal extension of a solid stream of cells segregated below somites 2 through 7. During its migration, cells are rearranged so that a short, wide rudiment is extended to form a long, thin one of similar volume. The pronephric duct rudiment of Xenopus laevis (an anuran) shows no evidence of caudal migration. Rather, pronephric duct cells are segregated out in situ by the formation of a fissure which separates them from the lateral plate mesoderm over ten somite widths. The chick pronephric duct forms a part of the intermediate mesoblast that extends by a caudal migration which does not, however, involve extensive cell rearrangements. Instead, cells near the tip of the duct rudiment in the chick proliferate, extending the duct by true growth as well as by active cell locomotion.
Topics: Ambystoma; Animals; Chick Embryo; Embryo, Nonmammalian; Kidney; Microscopy, Electron, Scanning; Nephrons; Species Specificity; Xenopus
PubMed: 6740242
DOI: No ID Found -
Development (Cambridge, England) Aug 2011Intracellular Ca²⁺ signals influence gastrulation, neurogenesis and organogenesis through pathways that are still being defined. One potential Ca²⁺ mediator of...
Intracellular Ca²⁺ signals influence gastrulation, neurogenesis and organogenesis through pathways that are still being defined. One potential Ca²⁺ mediator of many of these morphogenic processes is CaMK-II, a conserved calmodulin-dependent protein kinase. Prolonged Ca²⁺ stimulation converts CaMK-II into an activated state that, in the zebrafish, is detected in the forebrain, ear and kidney. Autosomal dominant polycystic kidney disease has been linked to mutations in the Ca²⁺-conducting TRP family member PKD2, the suppression of which in vertebrate model organisms results in kidney cysts. Both PKD2-deficient and CaMK-II-deficient zebrafish embryos fail to form pronephric ducts properly, and exhibit anterior cysts and destabilized cloacal cilia. PKD2 suppression inactivates CaMK-II in pronephric cells and cilia, whereas constitutively active CaMK-II restores pronephric duct formation in pkd2 morphants. PKD2 and CaMK-II deficiencies are synergistic, supporting their existence in the same genetic pathway. We conclude that CaMK-II is a crucial effector of PKD2 Ca²⁺ that both promotes morphogenesis of the pronephric kidney and stabilizes primary cloacal cilia.
Topics: Animals; Calcium-Calmodulin-Dependent Protein Kinase Type 2; Carrier Proteins; Cilia; Embryo, Nonmammalian; Enzyme Activation; Gene Expression Regulation, Developmental; Gene Expression Regulation, Enzymologic; Polycystic Kidney Diseases; TRPP Cation Channels; Zebrafish; Zebrafish Proteins
PubMed: 21752935
DOI: 10.1242/dev.066340 -
Developmental Biology Nov 2006The mechanisms by which a subset of mesodermal cells are committed to a nephrogenic fate are largely unknown. In this study, we have investigated the role of retinoic...
The mechanisms by which a subset of mesodermal cells are committed to a nephrogenic fate are largely unknown. In this study, we have investigated the role of retinoic acid (RA) signalling in this process using Xenopus laevis as a model system and Raldh2 knockout mice. Pronephros formation in Xenopus embryo is severely impaired when RA signalling is inhibited either through expression of a dominant-negative RA receptor, or by expressing the RA-catabolizing enzyme XCyp26 or through treatment with chemical inhibitors. Conversely, ectopic RA signalling expands the size of the pronephros. Using a transplantation assay that inhibits RA signalling specifically in pronephric precursors, we demonstrate that this signalling is required within this cell population. Timed antagonist treatments show that RA signalling is required during gastrulation for expression of Xlim-1 and XPax-8 in pronephric precursors. Moreover, experiments conducted with a protein synthesis inhibitor indicate that RA may directly regulate Xlim-1. Raldh2 knockout mouse embryos fail to initiate the expression of early kidney-specific genes, suggesting that implication of RA signalling in the early steps of kidney formation is evolutionary conserved in vertebrates.
Topics: Aldehyde Oxidoreductases; Animals; Body Patterning; Cell Lineage; Cytochrome P-450 Enzyme System; Embryo, Nonmammalian; Gastrula; Gene Expression Regulation, Developmental; Genes, Reporter; Homeodomain Proteins; Humans; LIM-Homeodomain Proteins; Mesoderm; Mice; Nephrons; PAX8 Transcription Factor; Paired Box Transcription Factors; RNA, Messenger; Receptors, Retinoic Acid; Retinoic Acid 4-Hydroxylase; Retinoic Acid Receptor alpha; Signal Transduction; Transcription Factors; Tretinoin; Xenopus Proteins; Xenopus laevis
PubMed: 16979153
DOI: 10.1016/j.ydbio.2006.06.047 -
Xenopus Pax-2 displays multiple splice forms during embryogenesis and pronephric kidney development.Mechanisms of Development Dec 1997Kidney organogenesis is initiated with the formation of the pronephric kidney and requires Pax-2 gene function. We report here the cloning and characterization of Pax-2...
Kidney organogenesis is initiated with the formation of the pronephric kidney and requires Pax-2 gene function. We report here the cloning and characterization of Pax-2 cDNAs from the frog Xenopus laevis, a model system suitable for the study of early kidney organogenesis. We show that expression of Xenopus Pax-2 (XPax-2) genes was confined to the nervous system, sensory organs, the visceral arches, and the developing excretory system. DNA sequencing of XPax-2 cDNAs isolated from head and pronephric kidney libraries revealed seven novel alternatively spliced Pax-2 isoforms. They all retain DNA-binding domains, but can differ significantly in their C termini with some isoforms containing a novel Pax-2 exon. We investigated the spectrum of XPax-2 splice events in pronephric kidneys, animal cap cultures and in whole embryos. Splicing of XPax-2 transcripts was found to be extensive and temporally regulated during Xenopus embryogenesis. Since all investigated tissues expressed essentially the full spectrum of XPax-2 splice variants, we conclude that splicing of XPax-2 transcripts does not occur in a tissue-specific manner.
Topics: Alternative Splicing; Amino Acid Sequence; Animals; Cloning, Molecular; DNA-Binding Proteins; Embryo, Nonmammalian; Gene Expression Regulation, Developmental; Growth Substances; Kidney; Molecular Sequence Data; Nervous System; PAX2 Transcription Factor; Sense Organs; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Tissue Distribution; Transcription Factors; Transcription, Genetic; Xenopus laevis
PubMed: 9486533
DOI: 10.1016/s0925-4773(97)00158-5 -
Developmental Biology Jul 2004The embryonic kidneys of larval aquatic vertebrates such as fish and frogs serve as excellent model systems for exploring the early development of nephric organs. These... (Comparative Study)
Comparative Study
The embryonic kidneys of larval aquatic vertebrates such as fish and frogs serve as excellent model systems for exploring the early development of nephric organs. These experimental systems can easily be manipulated by microsurgery, microinjection, genetics, or combinations of these approaches. However, little is known about how physiologically similar these simple kidneys are to the more complex mammalian adult kidneys. In addition, almost nothing is known about proximo-distal patterning of nephrons in any organism. In order begin to explore the physiological specialization of the pronephric tubules along the proximo-distal axis, a combination of uptake assays using fluorescently tagged proteins, LDL particles and dextrans, and an informatics-targeted in situ screen for transport proteins have been performed on embryos of the frog, Xenopus laevis. Genes identified to be expressed within unique subdomains of the pronephric tubules include an ABC transporter, two amino acid cotransporters, two sodium bicarbonate cotransporters, a novel sodium glucose cotransporter, a sodium potassium chloride cotransporter (NKCC2), a sodium chloride organic solute cotransporter (ROSIT), and a zinc transporter. A novel combination of colorimetric and fluorescent whole-mount in situ hybridization (FCIS) was used to precisely map the expression domain of each gene within the pronephros. These data indicate specialized physiological function and define multiple novel segments of the pronephric tubules, which contain at least six distinct transport domains. Uptake studies identified functional transport domains and also demonstrated that early glomeral leakage can allow visualization of protein movement into the pronephric tubules and thus establish a system for investigating experimentally induced proteinuria and glomerulonephritis.
Topics: Animals; Biological Transport, Active; Body Patterning; Colorimetry; Epithelium; Gene Expression Profiling; Gene Expression Regulation, Developmental; Gene Library; In Situ Hybridization, Fluorescence; Kidney Tubules; Membrane Transport Proteins; Monosaccharide Transport Proteins; Terminology as Topic; Xenopus laevis
PubMed: 15223337
DOI: 10.1016/j.ydbio.2004.03.036 -
Pflugers Archiv : European Journal of... Sep 2008Endocytic receptors in the proximal tubule of the mammalian kidney are responsible for the reuptake of numerous ligands, including lipoproteins, sterols, vitamin-binding...
Endocytic receptors in the proximal tubule of the mammalian kidney are responsible for the reuptake of numerous ligands, including lipoproteins, sterols, vitamin-binding proteins, and hormones, and they can mediate drug-induced nephrotoxicity. In this paper, we report the first evidence indicating that the pronephric kidneys of Xenopus tadpoles are capable of endocytic transport. We establish that the Xenopus genome harbors genes for the known three endocytic receptors megalin/LRP2, cubilin, and amnionless. The Xenopus endocytic receptor genes share extensive synteny with their mammalian counterparts. In situ hybridizations demonstrated that endocytic receptor expression is highly tissue specific, primarily in the pronephric kidney, and did not occur prior to neurulation. Expression was strictly confined to proximal tubules of the pronephric kidney, which closely resembles the situation reported in mammalian kidneys. By immunohistochemistry, we demonstrated that Xenopus pronephric tubule epithelia express high amounts of the endocytic receptors megalin/lrp2 and cubilin in the apical plasma membrane. Furthermore, functional aspects of the endocytic receptors were revealed by the vesicular localization of retinol-binding protein in the proximal tubules, probably representing endocytosed protein. In summary, we provide here the first comprehensive report of endocytic receptor expression, including amnionless, in a nonmammalian species. Remarkably, renal endocytic receptor expression and function in the Xenopus pronephric kidney closely mirrors the situation in the mammalian kidney. The Xenopus pronephric kidney therefore represents a novel, simple model for physiological studies on the molecular mechanisms underlying renal tubular endocytosis.
Topics: Animals; Chromosome Mapping; DNA, Complementary; Endocytosis; Gene Expression Profiling; Immunohistochemistry; In Situ Hybridization; Kidney; Kidney Tubules, Proximal; Low Density Lipoprotein Receptor-Related Protein-2; Membrane Proteins; Microscopy, Electron; Phylogeny; Proteins; Receptors, Cell Surface; Systematized Nomenclature of Medicine; Xenopus
PubMed: 18551302
DOI: 10.1007/s00424-008-0488-3