Abstracts - Society for Developmental Biology

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mutants, but is retained at the cell surface in vangl2 KOs. Similarly the distribution of Prickle-like2, a putative Vangl2
interacting protein, is differentially affected in the two lines. We propose that altered Vangl2S464N trafficking prevents
the delivery of multiple polarity proteins to the cell surface and that this net effect underlies the dominant phenotypic traits
associated with the Looptail mutation. One interpretation is that prior genetic interactions with Looptail may be indirect
and reflect a permissive enhancement of this semi-dominant phenotype.
Program/Abstract # 22
miRNA-mediated regulation of shoot maturation in plants
Yang, Li; Willmann, Matthew; Park, Mee Yeon; Wu, Gang; Poethig, Scott, University of Pennsylvania, Philadelphia,
United States
A plant shoot changes with time. Some changes occur quickly and are associated with major alterations in shoot
architecture, whereas others occur gradually and may have no obvious morphological manifestation. Microarray analysis
of gene expression in shoot apices, leaf primordia, and fully-expanded leaves of early (FRI flc-3) and late-flowering (FRI
FLC) genotypes of Arabidopsis revealed six major temporal programs. Three of these programs are features of leaf
development (leaf maturation, leaf aging, leaf senescence), and three involve changes in the character of the entire shoot
(vegetative phase change, flower induction,aging). We are particularly interested in the mechanism of vegetative phase
change—the transition from a juvenile toan adult phase of shoot development. This process is regulated by a decrease in
the expression of two related microRNAs miR156 and miR157, which act to promote the expression of the juvenile phase.
Ablation studies reveal that this decline is mediated by a factor(s) produced by existing leaf primordia, which acts on
newly formed primordia. Evidence indicating that this factor is a sugar will be presented.
Program/Abstract # 24
The recruitment of poised Pol II is regulated over developmental time
Gaertner, Bjoern; Chen, Kai; Shao, Wanqing; Meier, Sam; Johnston, Jeff ; Zeitlinger, Julia, Stowers Inst for Medical
Research, Kansas City, United States
Poised RNA polymerase II (Pol II) is predominantly found at developmental control genes and is thought to allow their
rapid and synchronous induction in response to extracellular signals. However, whether the recruitment of poised RNA Pol
II is itself regulated during development has not been explored. We have analyzed the genome-wide pattern of poised Pol
II during the activation of zygotic transcription in early Drosophila embryos, as well as by isolating muscle tissue at five
stages of differentiation. We show that the recruitment of poised Pol II is predominantly established during the second
wave of zygotic genome activation, also known as midblastula transition. During differentiation, many more genes acquire
poised Pol II over developmental time and this recruitment is associated with changes in chromatin. Furthermore, the
genome-wide pattern of poised Pol II helps predict future gene activation in a stage-specific but not tissue-specific fashion.
We conclude that the recruitment of poised Pol II is a checkpoint for developmental timing.
Program/Abstract # 25
Understanding and predicting cis-regulatory activity
Furlong, Eileen, EMBL-Heidelberg, Germany
The precise regulation of gene expression is crucial for almost all biological processes. In development, spatio-temporal
patterns of gene expression are controlled by extensive regulatory networks, where the activity of transcription factors
converge on cis-regulatory modules (CRMs) or enhancer elements. The location and even combinatorial occupancy of
CRMs can be experimentally measured using ChIP-seq at specific stages of development, at high-resolution. A current
major challenge however, is how to interpret these transcription factor's binding data in terms of the resulting spatiotemporal
enhancer activity. Using the integration of a machine learning approach with enhancers of known activity, we
recently demonstrated that transcription factor occupancy alone is sufficient to predict enhancer spatio-temporal activity
during development. We have now complemented this by generating cell-type specific information on chromatin state
within the context of a developing embryo using a new method that we developed called Batch Tissue Specific
ChIP(BiTS-ChIP). The data reveal heterogeneous combinations of chromatin marks linked to active enhancers. Using a
Bayesian network, we show that chromatin state is sufficient to predict, not just the location, but activity state of regulatory
elements, accurately distinguishing between enhancers in an active versus inactive state. The model revealed that Pol II
occupancy is highly predictive for the precise timing of enhancer activity and is tightly correlated with both the timing and
location of transcription factor occupancy. Taken together, this approach provides a systematic and high-resolution view of
dynamic enhancer usage during development, and essential step toward deciphering developmental networks.