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The Wnt antagonists Frzb-1 and Crescent locally regulate basement membrane dissolution in the developing primary mouth
Amanda J. G. Dickinson, Hazel L. Sive


The primary mouth forms from ectoderm and endoderm at the extreme anterior of the embryo, a conserved mesoderm-free region. In Xenopus, a very early step in primary mouth formation is loss of the basement membrane between the ectoderm and endoderm. In an unbiased microarray screen, we defined genes encoding the sFRPs Frzb-1 and Crescent as transiently and locally expressed in the primary mouth anlage. Using antisense oligonucleotides and `face transplants', we show that frzb-1 and crescent expression is specifically required in the primary mouth region at the time this organ begins to form. Several assays indicate that Frzb-1 and Crescent modulate primary mouth formation by suppressing Wnt signaling, which is likely to be mediated by β-catenin. First, a similar phenotype (no primary mouth) is seen after loss of Frzb-1/Crescent function to that seen after temporally and spatially restricted overexpression of Wnt-8. Second, overexpression of either Frzb-1 or Dkk-1 results in an enlarged primary mouth anlage. Third, overexpression of Dkk-1 can restore a primary mouth to embryos in which Frzb-1/Crescent expression has been inhibited. We show that Frzb-1/Crescent function locally promotes basement membrane dissolution in the primary mouth primordium. Consistently, Frzb-1 overexpression decreases RNA levels of the essential basement membrane genes fibronectin and laminin, whereas Wnt-8 overexpression increases the levels of these RNAs. These data are the first to connect Wnt signaling and basement membrane integrity during primary mouth development, and suggest a general paradigm for the regulation of basement membrane remodeling.


  • We thank members of the Sive lab, especially J. Gutzman, E. Graeden, A. Shkumatava and S. J. Hong for helpful comments and discussion, and V. Apekin for frog care and husbandry. For providing plasmids, we thank Thomas Czerny (pSGH2), Thomas Hollemann (pitx-3), Sally Moody (six-1) and Peter Good (nrp-1). Thanks to the Whitehead Center for Microarray Technology, especially Jen Love. Imaging was conducted using the W. M. Keck Foundation Biological Imaging Facility at the Whitehead Institute. Supported by NIH grant R21 DE017758-01 and, in the initial stages, by NSF grant IBN-0425030 to H.L.S., and a National Sciences and Engineering Research Council of Canada (NSERC) fellowship to A.J.G.D. Deposited in PMC for release after 12 months.

    • Accepted January 27, 2009.
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