Abstracts - Society for Developmental Biology

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assays, chromatin immunoprecipitation as well as transgenic studies further indicate that Cdx proteins operate via direct
binding to an evolutionary conserved neural crest enhancer of the Pax3 proximal promoter. Taken together, these results
suggest a novel neural function for Cdx proteins within the gene regulatory network controlling neural crest development.
Program/Abstract # 259
The transcription factor Sal-like 1 (Sall-1) is a direct transcriptional target of Wnt/beta-catenin signaling and
regulates neural patterning along with morphogenesis.
Young, John J.; Harland, Richard, University of California, Berkeley, United States
Amphibian neural development occurs as a two-step process: induction confers an anterior neural fate in undifferentiated
ectodermal precursors and transformation posteriorizes the portion that gives rise to the spinal cord and hindbrain.
Signaling through the Wnt pathway is necessary and sufficient to induce posterior fates in the neural plate. Despite
extensive knowledge about this signaling as a posteriorizing factor in neural development, the mechanism by which Wnt
signaling generates discrete domains of neural gene expression along the anterior-posterior axis remains poorly
understood. To address this question, we used RNA-Seq to identify direct transcriptional targets in neural tissue by
activating Wnt signaling in Xenopus neural explants pretreated with the translation inhibitor cycloheximide. Wnt-activated
neural tissue resulted in 262 genes expressed greater than two-fold when compared to anterior neural tissue. in situ
hybridization analysis of highly expressed transcription factors and RNA-binding proteins showed specific posterior neural
expression. Of particular interest, the transcription factor Sal-like 1 (Sall-1) showed specific posterior neural expression
suggesting a role in Wnt induce neural patterning. Chromatin immunoprecipitation using abeta-catenin specific antibody
revealed an enrichment of binding to a distal enhancer of Sall-1. Sall-1 overexpression posteriorizes the embryo as
evidenced by repression of the anterior cement gland and morpholino knockdown results in anteriorization, shown by a
loss of Krox-20 expression, a shortened axis anda failure to close the neural tube. Theseexperiments show Sall-1 is a direct
transcriptionaltarget of canonical Wnt signaling, is required for proper neural patterning, and links Wnt-induced patterning
with morphogenesis of the cells comprising the vertebrate neural axis.
Program/Abstract # 260
SOCS36E attenuates STAT signaling to facilitate proper cell migration in the Drosophila ovary
Monahan, Amanda; Starz-Gaiano, Michelle, University of Maryland in Baltimore County, Baltimore, United States
Cell migration plays a critical role in developing organisms. Thus, precise specification of migratory cell populations is
imperative. Border cell migration in Drosophila oogenesis provides an exemplary model to study acquisition of a
migratory state. The developing egg of Drosophila is composed of an epithelial monolayer surrounding sixteen germline
cells. At mid-oogenesis, two epithelial cells at the anterior secrete a paracrine signal, Unpaired (UPD)- the activating
ligand of the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway. Cells with the highest
levels of STAT activation become the migratory border cells; those with lower activation remain in the epithelium as
stretch cells. The border cells detach from the stretch cells and migrate to the oocyte, where they are required for egg
fertilization and development. Given the importance of this process, STAT signaling is regulated by a meticulous genetic
circuit. The transcription factorapontic (apt) functions in a negative feedback loop with STAT, partly through regulation of
mir-279. We have determined that suppressor of cytokine signaling (socs) 36e is also required for proper border cell
specification and migration. Null mutations in socs36e result in mis-specification of migratory cells and poor movement.
Genetic analysis suggests socs36e acts in the STAT regulatory circuit. We believe SOCS36E is needed downstream of
APT to attenuate STAT signaling, and thereby to establish a discrete division between the border and stretch cell fates.
Program/Abstract # 262
Nematostella reference transcriptome and high throughput gene regulatory network construction
Tulin, Sarah, MBL, Woods Hole, United States; Aguiar, Derek; Istrail, Sorin (Brown University, Computer Science
Department, Providence, RI, United States); Smith, Joel (MBL, Woods Hole, MA, United States)
Gene Regulatory Networks are a powerful tool to elucidate the important regulator yevents of embryogenesis. We are
studying the embryonic Gene Regulatory Network for the cnidarian, Nematostella vectensis, because its pivotal position in
the tree of life as the outgroup to Bilaterians will allow us, by comparing regulatory network architecture, to address key
outstanding questions about the evolution of body axis specification. As a first step in the network construction pipeline,
we have built a reference transcriptome from 0hr, 6hr, 12hr, 18hr and 24hr embryos using 100 bp paired end reads from
Illumina HiSeq 3rd generation chemistry. With the resulting 238 million high quality reads we assembled the transcriptome
into 88,684 transcripts using four distinct denovo and reference-based approaches. The de novo assembly was performed
using either Trinity or a combination of digital normalization, Velvet and Oases. These assemblies were compared to each
other and also compared to the method of assembly using the reference genome which was done through a separate