FAK is linked to aggressive tumors, but its normal function is not clear. FAK knockdown early in Xenopus development anteriorizes the embryo via a loss of Wnt signaling. Wnt3a expression is FAK dependent in both embryos and human breast cancer cells, suggesting that a FAK–Wnt linkage is highly conserved.

Recent studies connect the FAK and Wnt/β-catenin signaling pathways, both which promote cancer when aberrantly activated in mammalian cells. Over-stimulation of either Wnt/β-catenin or FAK activities was independently shown to promote numerous types of human cancers, including colon, breast, prostate and ovary. Observations in different model systems suggest a complex and dynamic cross-talk between these two pathways. During early vertebrate development, FAK protein is required for the proper regulation of Wnt/β- catenin signaling that controls pattern formation in the developing nervous system. In Xenopus laevis embryos, FAK protein depletion eliminated Wnt3a gene expression in the neural plate. In mouse osteoclast cells, mechanical stimulation through FAK activation stabilized β-catenin protein to promote its nuclear translocation. In contrast, in the mouse intestine, FAK activity was induced downstream of Wnt to promote intestinal regeneration and was also essential for tumorigenesis in an APC deletion model of colorectal cancer. Adding to this complexity, in human cell lines, FAK induced a context-dependent modulation of Wnt signaling to activate target-gene expression. Other diseases are also associated with FAK and Wnt pathway over-activation. Increased FAK and Wnt pathway activities were independently implicated in idiopathic pulmonary fibrosis (IPF), a lung disease of unknown etiology. Revealing the FAK-Wnt connection in IPF could provide a better understanding of disease pathology. There appear to be multiple interactions between the Wnt/β-catenin and FAK signaling pathways in different cell types and organisms. Mutual FAK-Wnt pathway regulation could be a general phenomenon, having many still undetermined roles in either normal physiological or disease processes.

Convergent extension is the primary driving force elongating the anteroposterior body axis. In Xenopus, convergent extension occurs in the dorsal mesoderm and posterior neural ectoderm, and is mediated by similar molecular pathways within these tissues. 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. This is seen in whole embryos, mesodermal explants and posterior neural explants, solidly implicating a role of NF-AT in convergent extension. In the whole embryo, inhibition of NF-AT reveals a more selective function, affecting only convergent extension in the neural ectoderm. This specific activity was further teased apart using a variety of temporal and spatial approaches. 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. Consistent with a function in neural convergent extension, we show that XNF-ATc3 is expressed and transcriptionally active within the neural tube. 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. Development 133, 1745Development 133, -1755Development 133, (2006 DEVELOPMENT 1746 movements within the neural ectoderm. This is the first evidence showing that NF-AT signaling has a role in neural CE movements and adds to a short list of molecules involved in this process. KEY WORDS: Convergent extension, NF-AT, Xenopus, Neural CE MATERIALS AND METHODS Injection and manipulation of Xenopus embryosRNA synthesis and Xenopus injection experiments were performed as described (Borchers et al., 2002). The plasmids CA XNF-AT, DN XNF-AT and WT XNF-AT used for RNA synthesis are a kind gift of Dr K. Mikoshiba (Saneyoshi et al., 2002). To represent the identity of the constructs better, we refer to them as CA XNF-ATc3, DN XNF-ATc3 and WT XNF-ATc3 in the text. For cyclosporin A (CsA) treatment, embryos were incubated in 4 mM or 400 M CsA (Bedford Laboratories) at time points indicated in the text. Cell adhesion assayFor cell adhesion assays stage 12.5-13 embryos were transferred into Ca 2+ /Mg 2+ -free medium CMFM (Sive et al., 2000) and neural plates were removed. After removal of the mesoderm, the neural tissue was transferred to a new dish containing CMFM and cells were manually dissociated using an eyebrow knife. If cells did not dissociate they were further agitated for 30 minutes. For re-aggregation single cells were transferred to 1/3 NMR. ␤ ␤-Galactosidase staining and whole mount in situ hybridization␤-Galactosidase staining and whole-mount in situ hybridization were performed as previously described (Borchers et al., 2002;Harland, 1991). Antisense probes were generated using the following plasmids: p33 En2 for engrailed (Brivanlou and Harland, 1989), pG1s for H...

The foxd1 gene (previously known as Brain Factor 2/BF2) is expressed during early Xenopus laevis development. At gastrula stages, foxd1 is expressed in dorsal mesoderm regions fated for muscle and notochord, while at neurula stages, foxd1 is expressed in the forebrain region. Previous studies in the neural plate showed that FoxD1 protein acts as transcriptional repressor downstream of BMP antagonism, neuralizing the embryo to control anterior neural cell fates. FoxD1 mesoderm function was not rigorously analyzed, but ectopic FoxD1 levels increased muscle marker expression in embryos. Using a FoxD1-specific antisense morpholino oligonucleotide, we knocked down endogenous FoxD1 protein activity in developing Xenopus embryos. In this present study, we show that FoxD1 is crucial for dorsal mesoderm formation. Analogous to neural tissue, FoxD1 acts downstream of BMP antagonism to induce dorsal mesoderm cell fates, such as muscle and notochord. FoxD1 is sensitive to its local signaling environment, having differential transcription factor activity in the presence or absence of Wnt or BMP signaling. FoxD1 induces posterior neural tissue in the presence of Wnt or BMP activities, but its activity is restricted to "normal" anterior neural tissue induction when BMP and Wnt activities are repressed. In dorsal mesoderm, FoxD1 interacts with Wnt signaling and BMP antagonism to induce muscle and notochord, while simultaneously repressing more anterior and ventral mesoderm cell fates. FoxD1 protein has multiple activities that are masked or released in the different germ layers as a function of the local signaling environment.

No abstract