title: The instructive role of metanephric mesenchyme in ureteric bud patterning, sculpting, and maturation and its potential ability to buffer ureteric bud branching defects.
abstract: Kidney organogenesis depends on reciprocal interactions between the ureteric bud (UB) and the metanephric mesenchyme (MM) to form the UB-derived collecting system and MM-derived nephron. With the advent of in vitro systems, it is clear that UB branching can occur independently of MM contact; however, little has been done to detail the role of MM cellular contact in this process. Here, a model system in which the cultured isolated UB is recombined with uninduced MM is used to isolate the effects of the MM progenitor tissue on the development and maturation of the collecting system. By morphometrics, we demonstrate that cellular contact with the MM is required for vectorial elongation of stalks and tapering of luminal caliber of UB-derived tubules. Expression analysis of developmentally significant genes indicates the cocultured tissue is most similar to an embryonic day 19 (E19) kidney. The likely major contributor to this is the functional maturation of the collecting duct and proximal nephron segments in the UB-induced MM, as measured by quantitative PCR, of the collecting duct-specific arginine vasopressin receptor and the nephron tubule segment-specific organic anion transporter OAT1, Na-P(i) type 2 cotransporter, and Tamm-Horsfall protein gene expressions. However, expression of aquaporin-2 is upregulated similarly in isolated UB and cocultured tissue, suggesting that some aspects of functional maturation can occur independently of MM cellular contact. In addition to its sculpting effects, the MM normalized a "branchless" UB morphology induced by FGF7 or heregulin in isolated UB culture. The morphological changes induced by the MM were accompanied by a reassignment of GFRalpha1 (a receptor for GDNF) to tips. Such "quality control" by the MM of UB morphology may provide resiliency to the branching program. This may help to explain a number of knockout phenotypes in which branching and/or cystic defects are less impressive than expected. A second hit in the MM may thus be necessary to make these defects fully apparent.
authors.affiliation: Department of Medicine, University of California, San Diego, California 92093-0693, USA.
authors.forename: Mita M
authors.initials: MM
authors.lastname: Shah
authors.forename: James B
authors.initials: JB
authors.lastname: Tee
authors.forename: Tobias
authors.initials: T
authors.lastname: Meyer
authors.forename: Catherine
authors.initials: C
authors.lastname: Meyer-Schwesinger
authors.forename: Yohan
authors.initials: Y
authors.lastname: Choi
authors.forename: Derina E
authors.initials: DE
authors.lastname: Sweeney
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Gallegos
authors.forename: Kohei
authors.initials: K
authors.lastname: Johkura
authors.forename: Eran
authors.initials: E
authors.lastname: Rosines
authors.forename: Valentina
authors.initials: V
authors.lastname: Kouznetsova
authors.forename: David W
authors.initials: DW
authors.lastname: Rose
authors.forename: Kevin T
authors.initials: KT
authors.lastname: Bush
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sakurai
authors.forename: Sanjay K
authors.initials: SK
authors.lastname: Nigam
mesh_terms: D000818:Animals; D018920:Coculture Techniques; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D005456:Fluorescent Dyes; D007150:Immunohistochemistry; D007668:Kidney / Q000033:anatomy & histology / Q000196:embryology*; D008648:Mesoderm / Q000502:physiology*; D046228:Microarray Analysis; D008845:Microinjections; D010641:Phenotype; D011247:Pregnancy; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012235:Rhodamines; D014599:Uterus / Q000002:abnormalities* / Q000033:anatomy & histology / Q000196:embryology*
chemical_list: D018076:DNA, Complementary; D005456:Fluorescent Dyes; D012235:Rhodamines