Congress Abstracts - Society for Developmental Biology

NSCs, but not in neurons, bind not only to genes that are expressed in NSCs, but also to silent genes that will become activated in
Sox11-positive neurons. Vice versa, Sox11, which is expressed in neurons but not in NSCs, binds to active neuronal genes as well as
to silent NSC genes that were previously targeted by Sox1-3. Moreover, in NSCs Sox1-3 also pre-bind genes that are specifically
expressed in Sox10-positive oligodendrocytes. Despite these broad binding profiles of Sox proteins in the developing nervous sytem,
in vitro studies show that Sox1-3 can specifically activate cis-regulatory elements (CREs) of NSC genes, while Sox11 and Sox10
specifically activate CREs of neuronal and oligodendrocyte genes, respectively. To examine how this functional specificity of Sox
proteins is regulated at the gene level, we are simultaneously analyzing thousands of Sox bound CREs in vitro using a multiplex
reporter assay. The goal of this project is to reveal binding motifs of potential partner factors, which confer functional specificity to
Sox proteins during the differentiation of neurons and oligodendrocytes from NSCs.
Program/Abstract # 114
Investigating direct targets of mSOX3 in neural progenitor cells
McAninch, Dale (University of Adelaide, Australia); Rogers, Nick; Thomas, Paul (Adelaide, Australia)
Intellectual disability (ID) affects 2-3% of the population, of which approximately 30% of cases are thought to be due to mutations in
genes on the X-chromosome. X-linked hypopituitarism is a form of syndromic ID that is caused by mutations and duplications of the
central nervous system transcription factor gene Sox3. In mice, Sox3 is expressed in neural progenitor cells (NPCs) throughout
embryogenesis and is important for maintaining them in their progenitor state. Published ChIP-seq data for mSOX3 in embryonic
stem (ES) cell-derived NPCs has identified more than 9000 mSOX3 binding sites across the genome, however little is known
regarding the function of these binding sites. To identify SOX3-regulated genes, genome-wide expression profiling was performed
comparing wild type and Sox3 null NPCs. 24 differentially expressed (DE) genes were identified in Sox3 null NPCs, 5 up regulated
and 19 down regulated, many of which have unknown functions and expression patterns. Next we performed a cross platform
comparison of the two datasets which revealed an 85% enrichment of mSOX3 binding sites neighbouring DE genes, compared with a
34% enrichment of binding sites near non-DE genes, suggesting that many of the DE genes are direct targets. Dbx1 is homeobox gene
that is down regulated in Sox3 knockout NPCs and expressed within a subset of Sox3 expressing NPCs in the developing mouse
embryo. We investigated Dbx1’s potential as a direct target by analysing five neighbouring evolutionary conserved mSOX3 binding
sites by ChIP-PCR analysis. All five sites were shown to enrich by ChIP-PCR, which, taken together with the down regulation in Sox3
null NPCs, suggests Dbx1 is a direct target of mSOX3.
Program/Abstract # 115
SOX9 directly modulates cell cycle regulators during post-EMT heart valve development.
Garside, Victoria C.; Cullum, Rebecca; Hoodless, Pamela (BC Cancer Agency, Terry Fox Labs, Canada)
The correct formation of the heart valves is critical for establishing proper blood flow during embryonic life as the load on the heart is
increasing. Abnormal heart valve formation leads to one third of all cardiovascular birth defects. These heart valve defects can have
detrimental effects on heart function throughout life and can lead to an increase in susceptibility to disease as an adult. A transcription
factor called SOX9, has a critical role in heart valve development, specifically in the proliferation and diversification of the heart
valve progenitor cells. The loss of SOX9 in the mouse heart valves leads to major valve abnormalities and results in embryonic
lethality. Although SOX9 is known to play critical roles in many organ systems, to date, there are few known transcriptional targets
of SOX9. To identify genome-wide transcriptional targets of SOX9 in E12.5 atrioventricular canal (AVC, valve forming region) and
limb, we performed chromatin immunoprecipitation coupled with sequencing (ChIP-Seq). For the first time, we have identified
thousands of potential SOX9 transcriptional targets in the E12.5 AVC and limb with 2607 and 9092 SOX9 sites, respectively.
Interestingly, Gene Ontology (GO) analysis on common SOX9 peaks revealed that SOX9 directly binds genomic regions of genes
required for cell cycle during valve development and, although a role for SOX9 in proliferation has been suggested, we have now
identified SOX9 target genes involved in this process. Additional studies are aimed at understanding the specific role of select SOX9
target genes involved in cell cycle in developing heart valves and will help to elucidate the role they play in heart valve regulatory
networks.
Program/Abstract # 116
Modulation of SoxE function in the Neural Crest by the SoxD family protein, Sox5
Nordin, Kara Marie (Northwestern University, USA)
SoxE transcription factors are essential Neural Crest (NC) regulatory factors. They act reiteratively throughout NC development to
promote the formation, maintenance and differentiation of NC cells. Interestingly, SoxE factors induce the formation of derivatives in
a context-dependent manner through a related Sox protein, Sox5, which is known to modulate SoxE function. We show that Xenopus
Sox5 is expressed in NC cells as well as in the paraxial mesoderm and pre-placodal ectoderm. We provide evidence that Sox5 plays an
early and essential role in patterning the ectoderm that is independent of SoxE factors. Loss of function experiments suggest that Sox5
promotes epidermal formation at the expense of both the neural plate and the neural plate border regions of the ectoderm. To
investigate later roles for Sox5 in the neural crest we generated a hormone inducible form of Sox5. Using this tool we find that while
Sox5 can cooperate with SoxE factors to activate the collagen type II (Col2a1) promoter, it inhibits SoxE mediated activation of
dopachrome tautomerase (Dct). To further investigate the context dependent functions of Sox5, we examined which protein domains
were required for its different functions. We show that dimerization is required in order for Sox5 to cooperate with SoxE factors on
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