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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.12.022 Byline: Adnan Mir (a)(b), Matthew Kofron (a), Janet Heasman (a), Melissa Mogle (a), Stephanie Lang (a), Bilge Birsoy (a), Chris Wylie (a) Keywords: FoxI1e; Xenopus; Ectoderm; Animal gene expression Abstract: Little is known of the control of gene expression in the animal hemisphere of the Xenopus embryo. Here we show that expression of FoxI1e, a gene essential for normal ectoderm formation, is expressed regionally within the animal hemisphere, in a highly dynamic fashion. In situ hybridization shows that FoxI1e is expressed in a wave-like fashion that is initiated on the dorsal side of the animal hemisphere, extends across to the ventral side by the mid-gastrula stage, and is then turned off in the dorsal ectoderm, the neural plate, at the neurula stage. It is confined to the inner layers of cells in the animal cap, and is expressed in a mosaic fashion throughout. We show that this dynamic pattern of expression is controlled by both short- and long-range signals. Notch signaling controls both the mosaic, and dorsal/ventral changes in expression, and is controlled, in turn, by Vg1 signaling from the vegetal mass. FoxI1e expression is also regulated by nodal signaling downstream of VegT. Canonical Wnt signaling contributes only to late changes in the FoxI1e expression pattern. These results provide new insights into the roles of vegetally localized mRNAs in controlling zygotic genes expressed in the animal hemisphere by long-range signaling. They also provide novel insights into the role of Notch signaling at the earliest stages of vertebrate development. Author Affiliation: (a) Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Ave, Cincinnati, OH 45229, USA (b) Physician/Scientist Training Program, P. O. Box 670555, Cincinnati, OH 45267, USA Article History: Received 6 September 2007; Revised 17 December 2007; Accepted 17 December 2007

Jun N[H.sub.2]-terminal kinases (JNKs) regulate convergent extension movements in Xenopus embryos through the noncanonical Wnt/ planar cell polarity pathway. In addition, there is a high level of maternal JNK activity spanning from oocyte maturation until the onset of gastrulation that has no defined functions. Here, we show that maternal JNK activation requires Dishevelled and JNK is enriched in the nucleus of Xenopus embryos. Although JNK activity is not required for the glycogen synthase kinase-3-mediated degradation of [beta]-catenin, inhibition of the maternal JNK signaling by morpholino-antisense oligos causes hyperdorsalization of Xenopus embryos and ectopic expression of the Wnt/[beta]-catenin target genes. These effects are associated with an increased level of nuclear and nonmembrane-bound [beta]-catenin. Moreover, ventral injection of the constitutive-active Jnk mRNA blocks [beta]-catenin-induced axis duplication, and dorsal injection of active Jnk mRNA into Xenopus embryos decreases the dorsal marker gene expression. In mammalian cells, activation of JNK signaling reduces Wnt3A-induced and [beta]-catenin-mediated gene expression. Furthermore, activation of JNK signaling rapidly induces the nuclear export of [beta]-catenin. Taken together, these results suggest that JNK antagonizes the canonical Wnt pathway by regulating the nucleocytoplasmic transport of [beta]-catenin rather than its cytoplasmic stability. Thus, the high level of sustained maternal JNK activity in early Xenopus embryos may provide a timing mechanism for controlling the dorsal axis formation. nucelocytoplasmic transport | Wnt

Early Xenopus embryos are large, and during the egg to gastrula stages, when there is little extracellular matrix, the cytoskeletons of the individual blastomeres are thought to maintain their spherical architecture and provide scaffolding for the cellular movements of gastrulation. We showed previously that depletion of plakoglobin protein during the egg to gastrula stages caused collapse of embryonic architecture. Here, we show that this is due to loss of the cortical actin skeleton after depletion of plakoglobin, whereas the microtubule and cytokeratin skeletons are still present. As a functional assay for the actin skeleton, we show that wound healing, an actin-based behavior in embryos, is also abrogated by plakoglobin depletion. Both wound healing and the amount of cortical actin are enhanced by overexpression of plakoglobin. To begin to identify links between plakoglobin and the cortical actin polymerization machinery, we show here that the Rho family GTPase cdc42, is required for wound healing in the Xenopus blastula. Myc-tagged cdc42 colocalizes with actin in purse-strings surrounding wounds. Overexpression of cdc42 dramatically enhances wound healing, whereas depletion of maternal cdc42 mRNA blocks it. In combinatorial experiments we show that cdc42 cannot rescue the effects of plakoglobin depletion, showing that plakoglobin is required for cdc42-mediated cortical actin assembly during wound healing. However, plakoglobin does rescue the effect of cdc42 depletion, suggesting that cdc42 somehow mediates the distribution or function of plakoglobin. Depletion of [alpha]-catenin does not remove the cortical actin skeleton, showing that plakoglobin does not mediate its effect by its known linkage through [alpha]-catenin to the actin skeleton. We conclude that in Xenopus, the actin skeleton is a major determinant of cell shape and overall architecture in the early embryo, and that plakoglobin plays an essential role in the assembly, maintenance, or organization of this cortical actin.

The cloning of cDNA that entails the encoding of the CHO2 antigen shows that CHO2 is a novel 66-kD COOH-terminal motor kinesin-like protein in cultured mammalian cells located at the interphase centrosome and mitotic cells. The CHO2 motor domain can support the in vitro gliding of microtubules and the sequence is 86% similar to HSET. The movement of microtubules with their plus end leading indicates that the antigen is a minus end directed motor.