title: An in vivo reporter of BMP signaling in organogenesis reveals targets in the developing kidney.
abstract: BACKGROUND
  Bone morphogenetic proteins (BMPs) regulate essential processes during organogenesis, and a functional understanding of these secreted proteins depends on identification of their target cells. In this study, we generate a transgenic reporter for organogenesis studies that we use to define BMP pathway activation in the developing kidney.
  
  
  RESULTS
  Mouse strains reporting on BMP pathway activation were generated by transgenically expressing beta-galactosidase under the control of BMP responsive elements from Id1. Reporter expression corresponds well with immunoassays for pathway activation in all organs studied, validating the model. Using these reporters we have generated a detailed map of cellular targets of BMP signaling in the developing kidney. We find that SMAD dependent BMP signaling is active in collecting duct trunks, but not tips. Furthermore, glomerular endothelial cells, and proximal nephron tubules from the renal vesicle stage onward show pathway activation. Surprisingly, little activation is detected in the nephrogenic zone of the kidney, and in organ culture BMP treatment fails to activate SMAD dependent BMP signaling in nephron progenitor cells. In contrast, signaling is efficiently induced in collecting duct tips.
  
  
  CONCLUSIONS
  Transgenic reporters driven by control elements from BMP responsive genes such as Id1 offer significant advantages in sensitivity and consistency over immunostaining for studies of BMP pathway activation. They also provide opportunities for analysis of BMP signaling in organ and primary cell cultures subjected to experimental manipulation. Using such a reporter, we made the surprising finding that SMAD dependent BMP signaling is inactive in nephron progenitors, and that these cells are refractory to activation by applied growth factors. Furthermore, we find that the BMP pathway is not normally active in collecting duct tips, but that it can be ectopically activated by BMP treatment, offering a possible explanation for the inhibitory effects of BMP treatment on collecting duct growth and branching.
authors.affiliation: Department of Molecular Medicine, Maine Medical Center Research Institute, 81 Research Drive, Scarborough, ME 04074, USA. Blanku@mmc.org
authors.forename: Ulrika
authors.initials: U
authors.lastname: Blank
authors.forename: Marianne L
authors.initials: ML
authors.lastname: Seto
authors.forename: Derek C
authors.initials: DC
authors.lastname: Adams
authors.forename: Don M
authors.initials: DM
authors.lastname: Wojchowski
authors.forename: Michele J
authors.initials: MJ
authors.lastname: Karolak
authors.forename: Leif
authors.initials: L
authors.lastname: Oxburgh
mesh_terms: D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018390:Gene Targeting; D017930:Genes, Reporter / Q000502:physiology*; D007668:Kidney / Q000196:embryology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008813:Mice, Inbred ICR; D008822:Mice, Transgenic; D038081:Organogenesis / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D051898:Smad1 Protein / Q000096:biosynthesis / Q000235:genetics; D051902:Smad5 Protein / Q000096:biosynthesis / Q000235:genetics; D051904:Smad8 Protein / Q000096:biosynthesis / Q000235:genetics; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics
chemical_list: D019485:Bone Morphogenetic Proteins; D051898:Smad1 Protein; D051902:Smad5 Protein; D051904:Smad8 Protein; D001616:beta-Galactosidase
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