JNK and ROKalpha function in the noncanonical Wnt/RhoA signaling pathway to regulate Xenopus convergent extension movements.

The Wnt/planar cell polarity (PCP) pathway plays a critical role in wing, eye, and sensory bristle development of Drosophila and in convergent extension (CE) movements during vertebrate gastrulation. In Drosophila, Jun N-terminal kinase (JNK) and Rho-associated kinase (ROK) participate in RhoA-mediated PCP pathway during eye and wing development. In mammalian cells, Rac1 and Cdc42 but not RhoA are required for JNK activation by Wnt/PCP signals. However, there has been no evidence that Rho GTPases regulate JNK activation in Wnt/PCP pathway during Xenopus CE movements. Here, we report that Xenopus RhoA (XRhoA), but not Xenopus Cdc42 (XCdc42), is essential for JNK activation downstream of the Wnt/PCP pathway during Xenopus CE movements, and the phenotypic effect of loss of XRhoA function was rescued by Xenopus JNK1 (XeJNK1). In addition, XRhoA rescues the inhibition of CE movements by the DEP domain deletion mutant of Xenopus Dsh (Xdsh-DeltaDEP), which has dominant negative (DN) effects on JNK activation, and the PDZ domain deletion mutant of Xdsh (Xdsh-DeltaPDZ). Moreover, we demonstrate that Xenopus Rho-associated kinase alpha (xROKalpha), which is expressed mainly in mesoderm and ectoderm that undergo extensive cell rearrangements, regulates CE movements without affecting gene expression, and injection of xROKalpha rescued the inhibition of CE movements caused by DN XRhoA. Finally, we show that ROKalpha and JNK synergistically rescued embryos overexpressing DN XRhoA, which exhibit gastrulation defects, although ROKalpha is not required for JNK activation. Together, these data suggest that JNK and ROKalpha function in the noncanonical Wnt/RhoA pathway to regulate Xenopus CE movements. Copyright 2005 Wiley-Liss, Inc.