Congress Abstracts - Society for Developmental Biology

Developmental cell signaling pathways relay patterning information to transcription factors (TFs), which in turn control cell fate by
regulating gene expression. Because these pathways are highly pleiotropic, we are particularly interested in how cis-regulatory DNA
sequences interpret such "generic" signals in a tissue-specific manner, and how they accurately read spatial information from
morphogen gradients. By altering the affinity of signal response elements in vivo, we have discovered important, sometimes surprising
roles for low-affinity, non-consensus binding sites for signal-regulated TFs in the regulation of the Drosophila genes wingless, dpp,
stripe, Pax2, and patched. In certain enhancers of these genes, weak binding is specifically required for proper responses to Hedgehog
or Notch signaling: improving binding affinity can either cause ectopic responses to a signal or, unexpectedly, switch the “sign” of the
response from activation to direct repression. This has important and complex implications for both the tissue specificity of responses
to signaling and the patterning of morphogen gradient responses. I will address the implications of our recent findings for genetic,
genomic, and computational approaches to the study of developmental transcriptional networks.
Program/Abstract # 20
Transcriptional and protein-protein networks in gynoecium and fruit development in Arabidopsis
Stefan de Folter, Víctor M. Zúñiga-Mayo, J. Irepan Reyes-Olalde, Paulina Lozano-Sotomayor, Daniela Ramos-Cruz, Jeanneth Pablo-
Villa, Humberto Herrera-Umbaldo, Mariana Sotelo-Silveira, Ricardo Chavez-Montes, Rocio Escobar-Guzmán, Karla González-
Aguilera (LANGEBIO, CINVESTAV-IPN, Mexico); Nayelli Marsch-Martínez (CINVESTAV-IPN, Mexico)
Gene regulation at the level of transcription is crucial for almost all biological processes in a cell or organism. Transcription factors
(TFs) are sequence-specific DNA-binding proteins that are capable of activating and/or repressing transcription. Many mutants
affected in development have been associated with altered expression levels of TF genes. Therefore, the analysis of TF genes can be
the basis for a better understanding of plant developmental processes. Our lab identified various novel TFs affecting gynoecium and
fruit development in Arabidopsis. At the moment, we are studying their genetic interactions and furthermore, to gain a better
understanding about how they function on the molecular level, matrix-based yeast two-hybrid screens are performed with known TFs
involved in meristem, flower, and fruit development. The latest results will be presented.
Program/Abstract # 21
Asymmetric localization and segregation of Cdx2 transcripts at the 8-cell stage facilitates development of pluripotent cell
lineage of mouse embryos
Krzysztof B.Wicher, Maria Skamagki, Agnieszka Jedrusik (Gurdon Inst., UK); Sujoy Ganguly (U of Cambridge, UK); Magdalena
Zernicka-Goetz, (Gurdon Inst., UK)
Sub-cellular transcript localization commonly provides spatial regulation of gene expression in metazoan development. However, it is
currently unknown whether early mammalian embryos use such a mechanism. Here we demonstrate dynamic localization of
transcripts for the trophectoderm transcription factor, Cdx2, to the apical cortex of blastomeres about to undertake the first cell fate
decision in living mouse embryos. We show that transcript localization depends on a cis-element in the 3’ part of the coding-region of
Cdx2, apical localization of aPKC zeta and an intact microtubule and actin cytoskeleton, a microtubule motor of the kinesin family.
Upon differentiative cell division, localized Cdx2 transcripts are inherited by outside, trophectoderm progenitor cells where they
relocalise to the apical cortex. Furthermore, we show that interfering with the localization machinery leads to elevated Cdx2 in inside
cells and, consequently, a significantly diminished number of pluripotent cells. Thus inheritance of Cdx2 transcripts by outside cells
contributes to their differentiation and enables dispossessed inside cells to follow pluripotent development.
Program/Abstract # 22
Involvement of Notch-mediated lateral inhibition and subsequent planar cell migration of Delta1-expressing cells in avian otic
placode formation
Yoshio Wakamatsu, Noriko Osumi, Hiroko Shida (Tohoku U, Japan)
Cranial sensory organs arise from cranial placodes, thickenings of ectodermal epithelium. These placodes originate from pre-placodal
region (PPR) surrounding anterior neural plate. We examined an expression of Delta1, which encodes a Notch ligand, in quail
embryos, and found that Delta1-positive cells initially emerged as a “salt-and-pepper” pattern at the prospective otic level of the PPR,
suggesting Notch-mediated lateral inhibition undergoing to select these cells. Consistently, forced activation of Notch signal in the
otic PPR disrupted otic placode formation, and an inhibition of Notch signal resulted in the expansion of the Delta1-positve area of the
otic PPR. As development proceeded, it appeared as if these Delta1-positive cells were gradually assembled to form the otic placode.
Immunofluorescence staining with anti-Delta1 antibody revealed that these Delta1-positive cells rarely contacted with the basal
membrane, had long cell processes extending over the apical surface of the PPR, and sometimes contacted each other via these
processes. No Delta1-expressing cell has delaminated from the otic PPR. These observations suggest that a subset of the PPR cells
may acquire the otic placode fate by the Notch-mediated lateral inhibition and that these cells may subsequently migrate within the
PPR epithelium to form the otic placode. Consistently, our time-lapse observation revealed that anti-Delta1-labeled otic PPR cells
appeared to migrate in a coalescing direction in cultured quail embryos. This study may provide a cell-biologically unique example of
cell migration and sorting within the developing epithelial tissues.
Program/Abstract # 23
BMP signaling in dorsoventral axial patterning
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