ABSTRACT:
Sivakumar2011_WntSignalingPathway
The secreted protein Wnt activates the
heptahelical receptor Frizzled on nieghboring cells. Activation of
Frizzled causes the recruitment of additional membrane proteins
which in turn result in 1) the activation of the protein
Dishevelled via phosphorylation and 2) the activation of a
heterotrimeric G protein of unknown type. Activation of Dishevelled
results in the down-regulation of the Beta-Catenin destruction
complex which causes ubiquitination of Beta-Catenin and its
ultimate degradation via the proteasome. Inhibition of the
Beta-Catenin destruction complex yields a higher cytosolic
concentration of Beta-Catenin, which enters the nucleus, binds
various transcriptional regulatory molecules including the TCF/LEF
class of proteins, and results in the transcription of TCF/LEF
target genes. Activation of the heterotrimeric G-protein pathway in
turn activates Phospholipase C which in turn catalyzes the
catalysis of PI(4,5)P2 into DAG and IP3.
Reference:
The Wnt
signalling pathway.
You Wnt
some, you lose some: oncogenes in the Wnt signaling
pathway.
Wnt
signaling pathway.
This model is described in the article:
A systems biology approach
to model neural stem cell regulation by notch, shh, wnt, and
EGF signaling pathways.
Sivakumar KC, Dhanesh SB, Shobana S,
James J, Mundayoor S.
OMICS 2011 Oct; 15(10): 729-737
Abstract:
The Notch, Sonic Hedgehog (Shh), Wnt, and EGF pathways have
long been known to influence cell fate specification in the
developing nervous system. Here we attempted to evaluate the
contemporary knowledge about neural stem cell differentiation
promoted by various drug-based regulations through a systems
biology approach. Our model showed the phenomenon of
DAPT-mediated antagonism of Enhancer of split [E(spl)] genes
and enhancement of Shh target genes by a SAG agonist that were
effectively demonstrated computationally and were consistent
with experimental studies. However, in the case of model
simulation of Wnt and EGF pathways, the model network did not
supply any concurrent results with experimental data despite
the fact that drugs were added at the appropriate positions.
This paves insight into the potential of crosstalks between
pathways considered in our study. Therefore, we manually
developed a map of signaling crosstalk, which included the
species connected by representatives from Notch, Shh, Wnt, and
EGF pathways and highlighted the regulation of a single target
gene, Hes-1, based on drug-induced simulations. These
simulations provided results that matched with experimental
studies. Therefore, these signaling crosstalk models complement
as a tool toward the discovery of novel regulatory processes
involved in neural stem cell maintenance, proliferation, and
differentiation during mammalian central nervous system
development. To our knowledge, this is the first report of a
simple crosstalk map that highlights the differential
regulation of neural stem cell differentiation and underscores
the flow of positive and negative regulatory signals modulated
by drugs.
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KC Sivakumar 
