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Cell Biology of Ureter Development

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BRIEF REVIEW www.jasn.org Cell Biology of Ureter Development † Adrian S. Woolf* and Jamie A. Davies *School of Biomedicine, University of Manchester, Manchester Academic Health Science Centre and Manchester Children’s Hospital, Manchester, United Kingdom; and †Centre for Integrative Physiology, Hugh Robson Building, University of Edinburgh, Edinburgh, United Kingdom ABSTRACT The mammalian ureter contains two main cell types: a multilayered water-tight ep- The nephric (or Wolffian) ducts (NDs) ithelium called the urothelium, surrounded by smooth muscle layers that, by gen- are a pair of epithelial tubes, each of which erating proximal to distal peristaltic waves, pump urine from the renal pelvis toward runs along the edge of the intermediate the urinary bladder. Here, we review the cellular mechanisms involved in the de- mesoderm near the body cavity. Each velopment of these tissues, and the molecules that control the process. We consider ND gives rise to a ureteric precursor, the the relevance of these biologic findings for understanding the pathogenesis of ureteric bud (UB), which grows into human ureter malformations. metanephric mesenchymal (MM) cells condensing out of intermediate meso- J Am Soc Nephrol 24: 19–25, 2013. doi: 10.1681/ASN.2012020127 derm. Normally, a single bud emerges from each ND near its distal (caudal) Molecule Abbreviation Box end, a precision facilitating optimal ALK Activin receptor-like kinase (growth factor receptor) interaction between the UB and MM, AngII Angiotensin II (growth factor) which are required to generate a single BMP Bone morphogenetic protein (growth factor) ureter-kidney functional unit of normal DLGH Discs-large homolog (intracellular scaffolding protein) 1–3 ERK Extracellular signal-regulated kinase (intracellular signaling molecule) shape and internal structure. ETV ETS transcription factor (transcription factor) In principle, normal budding could be FGFR Fibroblast growth factor receptor (growth factor receptor) controlled either by prepatterning within FOX Forkhead box (transcription factor) the duct itself or by external signals. FRAS Fraser syndrome (basement membrane molecule) FREM FRAS1-related extracellular matrix (basement membrane molecule) Experiments with explanted NDs provide GDNF Glial cell line-derived neurotrophic factor (growth factor) no evidence for a strong intrinsic pre- GATA GATA-binding factor (transcription factor) pattern. Instead, any part of the duct, even GFR GDNF family receptor (growth factor receptor) the more proximal (cranial) section lying HCN3 Potassium/sodium hyperpolarization-activated cyclic nucleotide-gated channel 3 (ion channel) alongside the mesonephric kidney, can HNF1B Hepatocyte nuclear factor 1B (transcription factor) be stimulated to emit ectopic UBs by KIT v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (growth factor applying select molecules,4–8 the actions receptor) of which are understood by considering MYOCD Myocardin (transcription factor associated protein) PAX Paired box (transcription factor) intracellular pathways under their con- PI3K Phosphatidylinositol 3-kinase (intracellular signaling molecule) trol7 (Figure 1). PLC Phospholipase C (intracellular signaling molecule) PTCH Patched (growth factor receptor) RET Rearranged during transfection (growth factor receptor) Published online ahead of print. Publication date ROBO Roundabout (growth factor receptor) available at www.jasn.org. ROCK Rho-associated protein kinase (intracellular signaling molecule) Correspondence: Dr.AdrianS.Woolf,Schoolof SMAD Homologs of Drosophila protein, mothers against decapentaplegic and Biomedicine, University of Manchester, Manchester Caenorhabditis elegans protein SMA (intracellular signaling molecule) Academic Health Science Centre and Manchester SHH Sonic hedgehog (growth factor) Children’s Hospital, Michael Smith Building, Ox- SLIT Slit homolog (growth factor) ford Road, Manchester, M13 9PT, UK, or Dr. Jamie SOX SRY-related HMG-box (transcription factor) A. Davies, Centre for Integrative Physiology, Hugh TBX T-box (transcription factor) Robson Building, 15 George Square, Edinburgh TGF Transforming growth factor (growth factor) EH8 9XD, UK. Email: [email protected]. TSHZ Teashirt (transcription factor) uk or [email protected] UPK Uroplakin (urothelial membrane protein) VANGL Van Gogh-like (planar cell polarity protein) Copyright © 2013 by the American Society of Nephrology J Am Soc Nephrol 24: 19–25, 2013 ISSN : 1046-6673/2401-19 19 BRIEF REVIEW www.jasn.org UB emergence is antagonized by AngII-mediated Sprouty-1 (SPRY1) greatest ERK/PI3K/PLC activation SMAD signaling but favored by ERK, downregulation,19,20 favor formation of move together and produce the bud.24 PI3K, and PLC activation. NDs express a solitary, correctly placed UB (Figure 2). This movement is also modulated by activin A, which acts in an autocrine An autocrine loop involving neuropep- ETV4 and ETV5, transcription factors manner to activate SMADs and prevent tide Y may enhance the commitment of upregulated by GDNF/RET signaling.24 budding. However, when an isolated ND these ND cells to budding.21 During UB branching, epithelial cells is treated with both an activin antagonist ND budding is preceded by increased become wedge shaped, implicating cyto- and a growth factor that activates ERK, epithelial proliferation22 and thicken- skeletal changes involving actin micro- PI3K, and PLC pathways, multiple buds ing to a pseudostratified epithelium.23 filaments. Indeed, mutation of genes emerge along its length. In such experi- RET signaling leads to rearrangement encoding for the actin depolymerizing ments, numerous normal diameter buds of ND cells such that those with the factors, cofilin 1 and destrin, affect rather than one large cyst are generated, implying a yet-to-be-defined lateral in- hibition mechanism whereby bud tip cells direct their immediate neighbors to remain quiescent. ND cells express various cell surface receptors, each of which binds pro- branching or antibranching factors. RET and FGFR2 receptor tyrosine ki- nases, and their GFRa and sulfated gly- cosaminoglycan coreceptors, bind GDNF and FGFs, activating ERK, PI3K, and PLC pathways driving UB emergence.9,10 Expression of such re- ceptors depends on duct cells express- ing the GATA3 transcription factor,11 and b-catenin, a multifunctional intra- cellular protein,12,13 and on nearby Figure 1. Intracellular pathways modulating UB emergence from the ND. Pathways that stromal cells synthesizing retinoic acid, encourage (green) and pathways that inhibit (red) bud emergence are depicted. (See also the Molecule Abbreviation Box.) an effector metabolite of vitamin A.14 The extent of intracellular signaling triggered by receptor tyrosine kinases is limited by the cytoplasmic protein sprouty-1, without which the ND pro- duces multiple ectopic buds.15 In addi- tion, signaling between SLIT2 and ROBO2,16 members of molecular fam- ilies first implicated in neural guidance, together with expression of FOXC1 transcription factor,2 guard against UB ectopia by limiting the cranial extent of the GDNF expression domain within intermediate mesoderm. As alluded to above, bud emergence is also antagonized by TGFb family mem- bers (activins and BMPs), autocrine and paracrine factors that bind ALK receptor threonine kinases, activating the SMAD Figure2. GrowthfactorscontrollingUBemergencefromtheND.Thecaudalpartoftheembryo, pathway.17 Normally, in vivo,SMADac- with the cloaca/urogenital sinus, is on the left of the diagram. Except near the MM, inhibitory tivation is favored along most of the signals such as BMP4 and activin dominate the molecular landscape. MM produces activators 18 ’ ND. By contrast, near the duct scaudal such as GDNF in addition to GREM1 and follistatin, which respectively antagonize the anti- end, MM secretes the BMP antagonist, branching factors BMP4 and activin. At this precise point, the balance between activation and Gremlin-1 (GREM1),17 and the RET inhibition favors emergence of a single UB. (See also the Molecule Abbreviation Box.) Note that agonist,GDNF;these,togetherwith mesonephric tubules are not formed by ND branching but arise from adjacent mesenchyme. 20 Journal of the American Society of Nephrology J Am Soc Nephrol 24: 19–25, 2013 www.jasn.org BRIEF REVIEW branching,25 as does inhibition of signals from the forming bladder.36 urine is not needed for longitudinal ROCK, a molecule driving actin rear- Thevesicouretericjunctionthenbe- growth, although these experiments do rangements.26,27 ROCK is itself modu- comes physically separated from the not rule out a more subtle, differentiation- lated by the planar cell polarity protein, opening of the ND, maintained in males optimizing influence conferred by urine VANGL2. 28 In vitro, UB epithelia undergo as the ejaculatory duct, as they are flow that, in mice, probably begins sev- apoptotic death if physically separated pushed apart by growth of the bladder eral days after UB initiation when the from MM, and mesenchymal-derived wall. metanephros has formed its first layers factors such as GDNF may facilitate UB of vascularized glomeruli (Figure 3). survival as well as emergence.29 The PAX2 Urothelia in both the ureter and blad- transcription factor is normally expressed FURTHER GROWTH der have evolved to stop movement of in the ND and the emerging bud and is AND DIFFERENTIATION urine back into the body. Prevention of antiapoptotic in the UB/collecting duct OF URETERIC EPITHELIA movement of water and solutes through lineage.30,31 Prominent
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