environment’’ for efficient expression of tissue-specific genes via

modulating high-order chromatin remodelling.

doi:10.1016/j.mod.2009.06.208

05-P004 – Withdrawn.

05-P005

Ddc, a candidate developmental gene in heart and its role in

disease

Adam Prickett, Ruth B. McCole, Reiner Schulz, Rebecca J. Oakey

Department of Medical & Molecular Genetics, King’s College London,

London, United Kingdom

Dopa Decarboxylase (Ddc) is an enzyme that plays a funda-

mental role in the biosynthesis of catecholamine neurotransmit-

ters and serotonin. A short form transcriptional variant of Ddc

called Ddc_exon1a which originates from an alternative promoter

at exon 1a, is highly expressed in the trabecular cardiomyocytes

during development of pre-natal heart and is progressively

silenced during post natal development. Ddc_exon1a has recently

been shown by our group to be epigenetically regulated via geno-

mic imprinting in mouse heart in a tightly regulated tissue-spe-

cific and transcriptional variant-specific manner. Ddc and

Ddc_exon1a show bi-allelic expression in all other tissues.

We aim to show by analysing Ddc+/ and Ddc/+ knockout mice

how ablation of Ddc_exon1a affects heart-specific development.

We also will look at downstream target genes using microarray

analysis. We predict that the knockout may affect compaction

of the myocardium during mid-gestation, which could lead to car-

diomyopathies in adults. It has recently been shown that Ddc

imprinting is controlled by epigenetic mechanisms via a differen-

tially methylated region located in CGI2 of adjacent Grb10,

another gene imprinted in development, CGI2 contains a putative

CTCF binding site. We present our current findings looking at

expression patterns of Ddc_exon1a and Grb10 in the mouse

embryo using immunohistochemistry, insitu hybridization and

qPCR. Furthermore we look at the role of the insulator protein

CTCF using ChIP analysis and RNAi knockdown, to assay binding

and function of this protein at this gene locus.

doi:10.1016/j.mod.2009.06.210

05-P006

Regulation of transcriptional elongation by spt5 during dro-

sophila development

Barbara Jennings1,2, Robert Harvey2, David Ish-Horowicz1

1Cancer Research UK, London Research Institute, London, United

Kingdom2UCL Cancer Institute, London, United Kingdom

Transcription elongation has become recognised as a critical

point of control during the expression of many genes during

development. For example, genome-wide screens for promoter

proximal paused RNAP II in Drosophila have revealed that

approximately 20% of genes in S2 culture cells, and 10% in early

embryos, have initiated transcription but are transcriptionally

paused. In both cases, the sets of paused genes are enriched for

genes known to respond to developmental cues and environmen-

tal stimuli.There is mounting evidence that the Spt5 protein pro-

vides a key junction between developmental regulators of

transcription and the core transcriptional elongation complex.

Mutations in Spt5 recovered from Drosophila and zebrafish that

compromise its ability to cause transcriptional pausing result in

discrete developmental defects, indicating that Spt5 mediates

gene specific regulation. Spt5 acts as both a negative and a posi-

tive regulator of elongation, and the switch between these activ-

ities at the promoter proximal checkpoint may provide a critical

point of regulation by contextual transcription factors.We have

characterized a missense mutation in Drosophila Spt5 (W049)

that affects the transcription of a subset of genes during

development. Expression of the gene even-skipped (eve) is

directly subject to repression mediated by Spt5. Enhancer-

reporter constructs reproducing expression of specific stripes of

eve expression are affected differentially by Spt5W049 indicating

that Spt5 can regulate transcription in an enhancer-specific

manner. The aim of our current work is to ascertain the

molecular mechanisms by which contextual transcription factors

regulate transcriptional pausing during development.

doi:10.1016/j.mod.2009.06.211

05-P007

X chromosome inactivation in murine extraembryonic develop-

ment at post-implantation stages

Catherine Corbel, Patricia Diabangouaya, Edith Heard

Institut Curie-CNRS UMR 3215, INSERM U934, Paris, France

X-chromosome inactivation (XCI) enables dosage compensa-

tion between XX females and XY males. It is an essential process

that occurs during early female development. Our project aims to

investigate the status and mechanism of XCI in female embryos

at post-implantation stages (E6.5-8). In the embryonic lineages of

mice, X inactivation is random, with either the paternal (Xp) or

maternal chromosome being affected. In cells of extraembryonic

tissues, imprinted X inactivation of the Xp chromosome is found.

We are interested in the potential differences between these two

types of XCI process during post-implantation development. The

inactive state of the Xp in extraembryonic tissues is thought to

be less stable than in embryonic tissues. Recently it was shown that

some genes are more prone to escape XCI than others in extraem-

bryonic tissues (Patrat et al, PNAS, 106:5198, 2009). al., 2009. PNAS

106, 5198). However little is known about the basis for this relative

instability and such variability. We have set out to use an ’ex ‘ex

vivo’ approach in order to evaluate the status of X-linked gene

silencing/reactivation in frozen sections of post-implantation

embryos. The epigenetic marks on the inactive X and the nuclear

organization of the X chromosome are being analyzed in different

tissues at precise developmental stages. This analysis is being car-

ried out both in wild type wild-type embryos and in mutants for

various factors thought to be involved in XCI.

doi:10.1016/j.mod.2009.06.212

S114 M E C H A N I S M S O F D E V E L O P M E N T 1 2 6 ( 2 0 0 9 ) S 1 1 3 – S 1 1 9