Congress Abstracts - Society for Developmental Biology

Program/Abstract # 1
Mechanical force controls chemical signals in creating plant pattern
Elliot Meyerowitz (Caltech, USA)
One pattern generated by the stem cells at the tip of each plant shoot – the shoot apical meristem – of flowering plants has held a
fascination for generations of biologists and mathematicians. This is the phyllotactic pattern, the pattern of leaves and flowers around
the stem. The most common such pattern is the spiral phyllotactic pattern, which creates the highly recognizable organization of
compound fruits such as pineapples, of flowers like roses, and of inflorescences such as sunflowers. The model plant Arabidopsis
thaliana also has a spiral phyllotaxis, and we have used genetic, genomic, and cell biological approaches to learn in detail how the
cells of the meristem collaborate to generate this pattern. The major chemical signal is auxin, which has a specific transport system, in
which a family of plasma membrane proteins directs the efflux of the hormone from cells. The efflux proteins are not uniformly
distributed, thereby causing efflux directionally, leading to a net flow of auxin in complex patterns across the surface of the meristem.
Auxin not only induces new primordia of leaves and flowers, but also changes the physical properties of the cell wall. These physical
changes alter the stress pattern in the meristem surface, which in turn regulates the position of the auxin efflux carrier in
anisotropically stressed cells. The feedback between auxin concentration and physical stress creates the dynamic auxin patterns that
cause successive auxin peaks at positions approximately 130-140 degrees around the stem, creating the spiral (and other patterns of)
phyllotaxis. The stress pattern in the meristem also regulates the microtubule cytoskeleton of meristematic cells, and consequently it
may also dictate the plane of cell division. The stress pattern may also determine directions of cellulose synthesis in the cell wall, and
thus the subsequent direction of cellular growth, and the anisotropy of cells – leading to changes in auxin flow, and, consequently,
feedbacks on the stress pattern.
Program/Abstract # 2
Unusual patterns of Hox cluster evolution
Peter Holland, Ferdinand Marletaz, Laura Ferguson, Jordi Papas, (Oxford, UK), Fei Xu (Chinese Academy of Science, China), Willie
Taylor (NIMR, UK), Pete Olson (Nat Hist Museum London, UK)
In the 1980s, the discovery of Hox gene clusters in very different animals paved the way for an integrated science in which principles
and processes of embryonic development could be compared between widely divergent evolutionary lineages. A picture has emerged
of a conserved Hox gene cluster pattering the ancient head-to-tail axis across all bilaterian animals. Yet there are modifications, and
these differences between species may be very helpful in our attempts to link genotype evolution to phenotype evolution. Using
examples from on-going research, I will discuss intriguing examples of Hox cluster breakage, Hox cluster expansion and Hox cluster
shrinkage.
Program/Abstract # 3
Regulation of gene expression by RNA polymerase II promoter pausing during mouse embryonic development
Megan Jane Wilson (Univ. of Otago, New Zealand)
Proximal-promoter pausing by RNA polymerase II (RNA-polII) is a key rate-limiting step in transcription initiation. Recent genomewide
studies using chromatin-immunoprecipitation to detect stalled RNA-polII have shown that promoter-pausing occurs for a number
of genes, particularly developmental control genes. This stalling is believed to be a mechanism of gene regulation, causing RNA-polII
to be paused near a promoter region, ready to respond to environmental or developmental cues. Two transcription elongation factors
DSIF and NELF control promoter stalling by RNA-polII. Our laboratory studies sex-specific differentiation of developing mouse
embryo tissues and we have utilized this system to study RNA polII stalling and its effect on gene expression over key developmental
stages. Using ChIP-seq with antibodies against RNApolII, we identified many promoters that have RNA-polII stalled in a sex-specific
manor in both gonad and head tissue at 13.5 dpc. This corresponded to differences in gene expression between the sexes for the
associated gene transcript (as assayed by qPCR). For some transcripts, RNA polII stalling marked them for future activation at a later
time point in development. In other cases, paused RNA polII was associated with genes that were becoming down regulated. This data
also reveals that promoter pausing can occur differently between sexes during development. We also have preliminary evidence that
indicates that components of NELF and DSIF complexes are expressed differently between the sexes during embryogenesis. Together
our data suggests that some genes are being poised to respond to a signal and then strongly upregulated, whereas transcription at other
genes is stalled but not activated, perhaps in the absence of an appropriate signal.
Program/Abstract # 4
Withdrawn
Program/Abstract # 5
Characterization of human developmental enhancers: from whole genomes to single SNPs
Alvaro Rada Iglesias (Univ. of Cologne, Germany)
Distal regulatory elements, such as enhancers, play a preponderant role in the establishment of cell-type and developmental-stage
specific gene expression profiles. However, these elements are difficult to identify, since they lack strong defining features and show
limited sequence conservation. In the first part of my talk, I will summarize my postdoctoral work, in which epigenomic approaches
were used to characterize the enhancer repertoire of pluripotent (i.e. human embryonic stem cells (hESC)) and multipotent (i.e. human
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