Wnt signaling pathway interactions in early anterior-posterior specification and
patterning
In most animal embryos the establishment of the anterior-posterior (AP) axis provides the necessary initial
coordinates for building an embryo, and as such, it is the most critical step during embryonic development. A
large body of work has determined that the AP axis is initially established by the localized activation of Wnt/ß-
catenin signaling at the future posterior end of the embryo in many animals. In general, posterior restriction of
Wnt/ß-catenin signaling creates a posterior-to-anterior morphogen gradient that activates and positions early
gene regulatory networks (GRNs) along the AP axis. These include the endomesodermal GRN at the posterior
pole, an equatorial mostly non-neural ectoderm GRN, and the anterior neuroectoderm (ANE) GRN around the
anterior pole. For the first time in any animal, we have discovered that this fundamental developmental
process depends on 3 different, but interconnected, Wnt signaling pathways (Wnt/ß-catenin, Wnt/JNK and
Wnt/PKC) in the sea urchin embryo. Importantly, comparison of functional and expression studies among
multiple deuterostome species, including vertebrates, strongly suggests that aspects of this AP Wnt signaling
network are conserved. The long-term goal of the studies in our lab is to use systems biology approaches along
with functional analyses to characterize the extracellular, intracellular and transcriptional components of this
network. These discoveries will likely provide insight into how dysregulation of Wnt-mediated AP patterning
can lead to developmental disruptions, including human birth defects. The objective of this proposal is to
establish the transcriptional GRNs activated downstream of the non-canonical Wnt/JNK and Wnt/PKC
pathways in the network and to uncover how extracellular and intracellular Wnt modulators influence the
activity of the these GRNs. The central hypothesis is that key interactions among the Wnt signaling pathways
occur at the extracellular, intracellular, and transcriptional level. The rationale is that by generating the
transcriptional GRNs activated by the non-canonical Wnt pathways in the network, we can uncover
interactions at that level to be used to determine how the extracellular and intracellular Wnt modulators are
integrated in the overall network. Aim1 will generate a model of the transcriptional GRNs activated by the
Wnt/JNK and Wnt/PKC signaling pathways, combining information from temporal ATAC-seq data with
existing temporal differential screen data that compared wild type embryos with Wnt/JNK and Wnt/PKC
knockdown embryos. In Aim2 we will perform functional gene perturbation studies on key nodes in our
network model from Aim 1 to further establish the initial GRN scaffold downstream of Wnt/JNK and Wnt/PKC
signaling and to define any key interactions among the pathways at the transcriptional level. Aim 3 will use
gene perturbation analyses on putative extracellular and intracellular Wnt modulators in order to better
characterize the pathway members used in the Wnt/JNK and Wnt/PKC transduction pathways, to identify
possible interactions among these modulators between the pathways, and to learn how these modulators affect
the emerging GRN created in Aims 1 and 2. The proposed research is significant because of the fundamental
importance of Wnt signaling in AP specification and patterning in animal embryos. The proposed work is
innovative because, more broadly, it will be one of the few systematic studies conducted to determine how Wnt
signaling networks influence development in an in vivo model system. In addition, it will also provide the
baseline for comparative functional studies of the GRN in other deuterostome model species, including
vertebrates, thereby filling in large gaps in our knowledge of the evolution of early AP specification and
patterning mechanisms.
