RhoA acts downstream of Wnt5 and Wnt11 to regulate convergence and extension movements by involving effectors Rho kinase and Diaphanous: use of zebrafish as an in vivo model for GTPase signaling.
Gastrulation shapes the early embryos by forming three germ layers, ectoderm, mesoderm and endoderm. In vertebrates, this process requires massive cell rearrangement including convergence and extension (CE) movements that involve narrowing and lengthening of embryonic tissues as well as cell elongation. Such polarization and movements require precise reorganization and regulation of the cytoskeleton network and cell adhesion. Rho small GTPases are key regulators for dynamic actin cytoskeleton. However, the signaling mechanisms underlying their functions in CE remain to be further elucidated. We have cloned the zebrafish Danio rerio rhoA and by capitalizing on the specific functional knockdown using morpholinos against rhoA and the availability of CE mutants defective in Wnt signaling, we showed that rhoA morphants were reminiscent to noncanonical wnt mutants with serious disruption in CE movements. Injection of rhoA mRNA effectively rescued such defects in wnt5 and wnt11 mutants. Furthermore, CE defects in rhoA knockdown or wnt mutants can be suppressed through functional bypass after ectopic expression of the two mammalian Rho effectors, the Rho kinase and Diaphanous (mDia). These results provide the first evidence that the RhoA in vivo acts downstream of Wnt5 and Wnt11 to effect, without affecting cell fates, on the CE movements in zebrafish embryos. Significantly, it elicits such effect via both effectors, Rho kinase and Dia. These findings also support the versatility of the zebrafish as a model to further investigate the roles of various classes of small GTPases in regulating cell dynamics in vivo.
Zhu
Shizhen
S
Cell Signaling and Developmental Biology Laboratory, National University of Singapore, 14 Science Drive 4, Singapore 117543, The Republic of Singapore.
Liu
Lihui
L
Korzh
Vladimir
V
Gong
Zhiyuan
Z
Low
Boon Chuan
BC
D000595:Amino Acid Sequence; D000818:Animals; D002465:Cell Movement; D004625:Embryo, Nonmammalian / Q000502:physiology; D020558:GTP Phosphohydrolases / Q000502:physiology*; D005775:Gastrula / Q000502:physiology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D017403:In Situ Hybridization; D047908:Intracellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051153:Wnt Proteins / Q000235:genetics / Q000502:physiology*; D000071818:Wnt-5a Protein; D015027:Zebrafish / Q000196:embryology* / Q000502:physiology; D029961:Zebrafish Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000032:analysis / Q000235:genetics / Q000502:physiology*
D047908:Intracellular Signaling Peptides and Proteins; D011518:Proto-Oncogene Proteins; D051153:Wnt Proteins; D000071818:Wnt-5a Protein; C092568:Wnt11 protein, zebrafish; C480282:Wnt5a protein, zebrafish; D029961:Zebrafish Proteins; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020558:GTP Phosphohydrolases; D020742:rhoA GTP-Binding Protein