Congress Abstracts - Society for Developmental Biology

Program/Abstract # 48
Modeling regulatory systems for sea urchin development
Isabelle Peter, Eric Davidson (Caltech, USA)
The formation of distinct cell fate specification domains occurs by means of spatial control of gene expression. At the system level,
gene regulatory network (GRN) models attempt to incorporate the complete gene regulatory apparatus which determines a specific
developmental process. Yet as these network models include an increasing number of regulatory genes, the outcome of the regulatory
interactions between them becomes less easily comprehensible. The sea urchin endomesoderm GRN consists of about 50 regulatory
genes and determines the formation of at least five different gene expression domains before the onset of gastrulation. A recently
developed Boolean model demonstrates that the experimentally established regulatory interactions which constitute the
endomesoderm GRN model are indeed largely sufficient to reconstruct the spatial and temporal regulatory gene expression patterns
observed during the first thirty hours of sea urchin development. Furthermore, perturbation of the Boolean model accurately predicted
the outcome of experimental perturbation. The Boolean model thus shows that GRN models are in principle sufficient to explain
progressive regulatory gene expression during development and it contributes to the formalization of regulatory processes. The
insights gained from this analysis are now being applied to a much more complex process of post-gastrular organogenesis, the
formation of the embryonic gut.
Program/Abstract # 49
A gene regulatory network for endomesodermal specification in a basal deuterostome.
Veronica Frances Hinman, Brenna McMauley (Carnegie Mellon, USA)
A central pursuit in developmental biology is to understand how maternal processes can generate an embryo with molecularly distinct
cell populations. A causal explanation for this requires a comprehensive gene regulatory network (GRN) model that can explain how
genes are expressed at exactly the right time and in the right cells. We will discuss our recent work that describes the GRN for one of
the most important events in early development, the specification and segregation endoderm and mesoderm, using the sea star, Patiria
miniata, as our model system . Sea stars are a class of Echinoderms that are considered to represent the basal mode of development
of this phylum and possibly of all deuterostomes. The simplicity of sea star early development allows us to provide a detailed
explanation of endomesderm specification. Sea stars undergo equal cleavage and generate a holoblastula of only several hundred cells.
Endomesoderm fated cells form at the vegetal pole of the early embryo. Later mesoderm fated cells will segregate as central
population surrounded by a torus of endoderm. We show that this process is regulated by a spatio temporal gradient of nuclear β
catenin. A maternally controlled transcriptional factor based GRN additionally provides timing control for gene activation to ensure a
robust response to nuclear β catenin. We will also discuss how these GRN topologies can evolve by altering the β catenin gradient
and other signaling pathways.
Program/Abstract # 50
Gene regulatory network of neural crest development
Maneeshi Prasad, (Northwestern, USA)
The Neural Crest (NC) is an embryonic stem cell population that is induced at the neural plate border in vertebrates and later
emigrates from the dorsal aspect of the developing neural tube, migrate extensively, and give rise to a large and diverse group of cell
types. A network of signaling pathways and transcription factors form the neural crest gene regulatory network (NC-GRN) that
regulates the induction, specification and migration of NC. These signaling gradients from the neural and non-neural ectoderm, and
mesoderm in the form of Wnt and BMP antagonists induce the expression of early neural crest specifiers, Snail, Twist and Sox9. But
not much is known about the downstream targets of these neural crest specifiers and their role during different stages of NC
development. However, the reiterative use of these factors during different stages of neural crest development suggests their role in
regulating different target genes in a temporally controlled manner. To better understand their role in NC-GRN it is essential to
decipher their targets during different stages of NC development. Using genome wide approaches such as ChIP-Seq and RNA-Seq, we
have identified new putative regulatory targets of these neural crest specifiers during premigratory stages of neural crest development
in Xenopus laevis embryos. These targets include genes involved in regulating EMT as well as maintaining stem cell state. We
confirmed the presence of known targets of these factors and also new putative targets that are involved in induction and migration
stages of NC development. These Sox9 and Twist targets will provide more insights into the role of these NC specifiers during
different stages of NC development and also elaborate their role in NC-GRN.
Program/Abstract # 51
The phosphorylation state of Drosophila Mad determines its choice between BMP and Wingless signaling
Edward Eivers, Marlyn Rios, Abigail Aleman, Daniel Lee, Matthew Juarez, Keristineh Vartanpour (CSU Los Angeles, USA)
Bone morphogenetic proteins (BMPs) and Wnts are growth factors that are known to regulate a broad range of cellular events such as
stem cell maintenance, cell differentiation and organogenesis, while dysfunctional signaling of either pathway can result in severe
developmental abnormalities. Here we describe a new molecular mechanism by which the phosphorylation state of the transcription
factor Mad determines its ability to transduce either BMP or Wingless (a Wnt ligand) signals in Drosophila cells. Previously, Mad was
thought to function in gene transcription only when phosphorylated by the BMP receptor. We now demonstrate that Mad is required
for canonical Wingless signaling specifically when in an unphosphorylated state, by forming a Mad-Pangolin-Armadillo Wnt
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