Function Of NEDD4L In The Early Development Of Xenopus Embryo

During the early vertebrate body plan formation, axis formation is an importantevent involving massive cell movement and morphogenesis. Convergent extension (CE)of dorsal mesoderm and neurectoderm coordinated by the evolutionarily conservednon-canonical Wnt/PCP signaling is reported to play a critical role in shaping thevertebrate embryos. Dishevelled (Dvl), a key mediator of Wnt/PCP signaling, isessential for the medial-lateral polarity formation in the cells undergoing convergentextension movements. Though the regulation of Dvl function has been extensivelystudied, it is still unknown the mechanism that the control of Dvl stability in theWnt/PCP signaling pathway. NEDD4L, a highly conserved HECT type E3ligase, hasbeen reported to regulate a variety of physiological processes, including expression ofion channel, neuronagenesis and cell polarity through targeting multiple substrates. It isreported that gross morphology of NEDD4L knockout mice appeared the same as wildtype at the early developmental stage, however, our study of NEDD4L function in theXenopus embryos suggestes that NEDD4L is required for the cellular polarity formationand convergent extension in the early Xenopus embryos.Biochemical experiments show that NEDD4L directly interacts with Dvl2andpromotes its ubiquitination for proteasomal degradation. We then reveal thephysiological functions of NEDD4L with Xenopus embryos. Gain-of and loss-offunction study indicates that NEDD4L specifically regulates convergent extensionmediated by Wnt/PCP pathway in the early Xenopus embryos. In the epistatic analysis,reducing Dvl2expression can largely rescue the cellular polarity and convergentextension defects in NEDD4L-depleted embryos and explants, suggesting that NEDD4Lis in involved in the regulation of convergent extension via Dvl2-mediatednon-canonical Wnt signaling. This conclusion is further confirmed by rescuing cellpolarity disorder caused by NEDD4L depletion with RhoA-V14mRNA. In addition, ourpreliminary study suggests that NEDD4L may also be involved in regulating themesodermal cell fate specification through FGF signaling pathway.In summary, NEDD4L is a critical factor regulating convergent extension in theearly development of Xenopus. NEDD4L promotes the polarity formation of cells undergoing the convergent extension through regulating the stability of Dvl2proteinand activity of downstream effectors including RhoA, thereby promoting the axisformation. Our findings shed important new light on uncovering the molecular basis ofconvergent extension and perfecting the signaling mechanism of regulating the cellbehavior in the morphogenesis.