Abstracts - Society for Developmental Biology

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versus asymmetric cell divisions critical to cell fate decisions. A polarity complex composed of the proteins aPKC-Par6-
Par3 maintains active Notch signaling in the most apical domain of rosette neural stem cells. Notch signaling is inhibited at
basolateral portions of the cell by Numb. We show here that inhibition of Notch signaling by treatment with the gammasecretase
inhibitor DAPT results in a reduction in symmetrical cell divisions and an increase in asymmetrical cell divisions,
and therefore increased production of neurons relative to neural stem cells. We also demonstrate that treatment with
aurothiomalate (ATM), a small molecule inhibitor that prevents formation of a functional aPKC-Par6-Par3 polarity
complex, disrupts the subcellular localization of Par3 and Numb and reduces the number of asymmetric cell division
events. Under these conditions, the extent of neuron production is reduced. Additionally, we show that rosettes require
active maintenance of apical/basal polarity, as ATM treatment disrupts these structures.
Program/Abstract # 377
The Bmp antagonist Noggin paradoxically induces the chondrogenic program in post-migratory, neural crestderived
facial mesenchyme
Buchtova, Marcela, Academy of Sciences Instit of Animal Physiology & Genetics, BRNO Czech Republic; Richman, Joy
(University of British Columbia, Vancouver, Canada)
The bone morphogenetic protein (BMP) antagonist, Noggin, and Retinoic acid (RA) have previously been shown to induce
a homeotic transformation within the face of chicken embryos. The maxillary prominence was converted into the
frontonasal mass, thereby duplicating the facial midline. (Lee et al. 2001). The phenotype consists of the formation of an
ectopic cartilage which acquires the identity of the interorbital septum. Here, we examined the genesis of the cartilage and
determined that a Noggin bead alone was sufficient to induce the cartilage. This transformation from osteogenic to
chondrogenic fate only occurred in stage 15 embryos. By stage 20, treated embryos lost various intramembranous bones in
the palate but did not form cartilage. To test whether Noggin could directly activate the chondrogenic program we created
micromass cultures from stage 15 and 20 maxillary prominence, transfected a Col2-Luciferase reporter gene, which is
based on the binding site for SOX5, SOX6 and SOX9 in Col2a1. Noggin treatment of stage 15 mesenchyme significantly
stimulated the reporter whereas Noggin treatment at stage 20 had no effect on Col2-LUC activity. The induction of SOX9
RNA by Noggin at stage 15 but not at stage 20 mirrored the stage-specific results from the luciferase reporter experiments.
Our results suggest that Noggin at early stages of craniofacial development takes on a different role, unrelated to being a
BMP antagonist. Instead, Noggin activates transcription factors that promote chondrogenesis. We conclude that the
response of the mesenchyme is altered at stage 20 due to changes in the molecular landscape. This work was supported by
GACR (grant 304/09/0725) to MB and CIHR grant toJMR.
Program/Abstract # 378
The Hippo pathway member Nf2 regulates trophectoderm/inner cell mass specification.
Cockburn, Katherine; Rossant, Janet,University of Toronto, Toronto Canada
The first lineages to be specified during mouse preimplantation development are the trophectoderm (TE) and the inner cell
mass (ICM). Proper segregation of these two lineages requires that TE-specific transcription factors such as Cdx2 be
restricted in their expression to the outer, future-TE cells of the embryo. This Cdx2 expression pattern is regulated by the
transcriptional co-activator Yap, whose nuclear localization and resulting transcriptional activity is controlled by the
kinases Lats 1 and 2 (Lats1/2). The factors acting upstream of Lats1/2, Yap and Cdx2 during TE/ICM specification have
not yet been described. Here, we demonstrate a role for the Hippo scaffolding protein Nf2 in the preimplantation embryo.
Injection of a dominant negative form of Nf2 (dnNf2) causes a cell autonomous accumulation of Yap in the nuclei of
inside cells of the embryo, where it is normally cytoplasmic, and an increase in Cdx2 expression in these cells, where it is
usually absent. Consistent with an role upstream of Lats1/2, the effects of dnNf2 injection can be rescued by overexpression
of wild-type Lats2. In contrast to the strong and consistent effects of dnNf2 injection, we find that Nf2-/-
embryos have mild defectsin Yap localization and Cdx2 expression, and that these defects become more severe as
blastocyst development proceeds. Additionally, in wildtype embryos, Nf2 mRNA and protein can be detected before the
onset of zygotic transcription, suggesting that maternally supplied Nf2 is masking a stronger phenotype in these mutants.
Taken together, our results demonstrate that Nf2 acts upstream of Lats1/2 and Yap to regulate Cdx2, and that maternally
supplied Nf2 may play an important role during TE/ICM specification.
Program/Abstract # 379
Identification of transcription factors involved in differentiation of late-born ventral spinal neurons
Di Bella, Daniela, Fundación Instituto Leloir, Buenos AiresArgentina; Carcagno, Abel; Petracca, Yanina; Sartoretti,
Micaela (Fundación Instituto Leloir, Buenos Aires, Argentina); Goulding, Martyn (Salk Institute, La Jolla, CA, United
States); Lanuza, Guillermo (Fundación Instituto Leloir, Buenos Aires, Argentina)