A role for microfilament-based contraction in branching morphogenesis of the ureteric bud.
BACKGROUND
Branching morphogenesis of the ureteric bud/collecting duct epithelium is an important feature of kidney development. Recent work has identified many transcription factors and paracrine signaling molecules that regulate branching, but the physical mechanisms by which these signals act remain largely unknown. The actin cytoskeleton is a common component of mechanisms of morphogenesis. We have therefore studied the expression of, and requirement for actin filaments in the ureteric bud, a branching epithelium of the mammalian kidney.


METHODS
Embryonic kidney rudiments were grown in organ culture. Actin expression in kidneys growing normally and those in which branching was inhibited was examined using labeled phalloidin. The morphogenetic effects of inhibiting actin organization and tension using cytochalasin D, butanedione monoxime, and Rho kinase ROCK inhibitors were assessed using immunofluorescence.


RESULTS
F-actin is expressed particularly strongly in the apical domains of cells at the tips of branching ureteric bud, but this expression depends on the bud actively growing and branching. Blocking the polymerization of actin using cytochalasin D inhibits ureteric bud branching reversibly, as does blocking myosin function using butadiene monoxime. Inhibiting the activation of ROCK, a known activator of myosin, with the drugs Y27632 or with H1152 inhibits the expression of strong actin bundles in the ureteric bud tips and inhibits ureteric bud branching without inhibiting other aspects of renal development.


CONCLUSIONS
The formation of tension-bearing actin-myosin complexes is essential for branching morphogenesis in the developing kidney.
Michael
Lydia
L
Centre for Integrative Physiology, Edinburgh University College of Medicine, Scotland, UK.
Sweeney
Derina E
DE
Davies
Jamie A
JA
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D000199:Actins / Q000187:drug effects / Q000502:physiology; D000818:Animals; D016764:Cell Polarity / Q000502:physiology; D015638:Cytochalasin D / Q000494:pharmacology; D004847:Epithelial Cells / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000196:embryology* / Q000502:physiology*; D051379:Mice; D009218:Myosins / Q000502:physiology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D009924:Organ Culture Techniques; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014513:Ureter / Q000166:cytology / Q000196:embryology* / Q000502:physiology*; D054460:rho-Associated Kinases
D000199:Actins; D047908:Intracellular Signaling Peptides and Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D015638:Cytochalasin D; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D009218:Myosins