The integration of pathways, like the Wnt/Ca 2+ or PCP, to coordinate cellular movements will most certainly involve the modification and activation of different and diverse downstream transcriptional targets. It remains unknown how these two pathways are integrated into coordinating distinct cellular movements, although as these pathways share molecules and functions,it is likely that there is extensive crosstalk between the various players as well as possible subtle modifications of downstream targets( Elul and Keller, 2000 Elul et al., 1997 Ezin et al., 2003 Shih and Keller, 1992a Shih and Keller, 1992b). Although the PCP and Wnt/Ca 2+ pathways instruct morphogenesis in both the neural ectoderm and dorsal mesoderm, the behavior and morphology of cells undergoing CE is different within these cellular populations. These pathways, under control of the secreted ligands Wnt11, Wnt5a and Wnt4, do not activate β-catenin signaling ( Moon et al., 1993 Torres et al.,1996), but rather either function to release calcium(Wnt/Ca 2+ pathway) ( Slusarski et al., 1997a Slusarski et al., 1997b) or regulate PCP pathway members like strabismus,prickle, JNK, Daam1 or dishevelled( Wallingford et al., 2002). Two types of non-canonical Wnt pathways have been described that mediate both posterior neural ectodermal and dorsal mesodermal CE the planar cell polarity (PCP) pathway ( Keller,2002 McEwen and Peifer,2000 Peifer and McEwen,2002) and the Wnt/Ca 2+ pathway( Kuhl et al., 2000). This work identifies XNF-ATc3 as a regulator of neural convergent extension in Xenopus and adds to a short list of molecules involved in this process. Consistent with a function in neural convergent extension, we show that XNF-ATc3 is expressed and transcriptionally active within the neural tube. Targeted injections of dominant-negative XNF-ATc3, or dosing over time with the calcineurin inhibitor cyclosporin in neural tube explants or in whole embryos, shows that inhibition of NF-AT signaling blocks neural convergent extension. This specific activity was further teased apart using a variety of temporal and spatial approaches. In the whole embryo, inhibition of NF-AT reveals a more selective function, affecting only convergent extension in the neural ectoderm. ![]() This is seen in whole embryos, mesodermal explants and posterior neural explants, solidly implicating a role of NF-AT in convergent extension. In this paper, we show that activation of NF-AT, a transcription factor known to modulate multiple signaling events, inhibits convergent extension in the dorsal mesoderm and in the posterior neural ectoderm. ![]() In Xenopus, convergent extension occurs in the dorsal mesoderm and posterior neural ectoderm, and is mediated by similar molecular pathways within these tissues. ![]() Convergent extension is the primary driving force elongating the anteroposterior body axis.
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