Epigenetic and cis-regulation of gene
networks during embryogenesis in
Drosophila and mouse
|
|
|
|
|
|
|
|
In the past decade the genomes of
many organisms have been completely sequenced. Two striking observations
are that these genomes contain significantly fewer genes than originally
predicted and that the majority of the DNA sequence contains regions of
presently unknown function. It is therefore clear that
the vastly increased biological complexity of higher eukaryotes is critically
dependent on the tightly directed expression of gene networks during their
development. Our research interests lie specifically in the role
of this presently uncharacterized genomic DNA in epigenetic and cis-regulation
of gene expression during embryonic development. Applying genetic
manipulations in mouse and Drosophila we intend to use model
gene networks such as the homeotic complexes in Drosophila and imprinted
loci in mice and humans as paradigms to analyze the functional activities
of novel regulatory DNA sequences. Our research also examines the
functional activities of epigenetic events such as DNA methylation, transcription
of non-coding intergenic RNAs and chromatin remodeling.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Promoter-enhancer interactions
in the Bithorax gene complex
|
|
|
|
|
|
|
|
We have been examining the mechanism
by which transcriptional enhancers are selectively recruited to specific
promoters in gene complexes. In the Bithorax complex of
Drosophila two divergently transcribed genes, AbdB
and abdA, are separated by a 100 kb intergenic region which harbors
the IAB5 enhancer. Although equidistant from the promoters of these
two genes, this enhancer is specifically recruited only to the AbdB
promoter and functions to maintain the restricted expression of AbdB
during gastrulation. Transgenic experiments which we performed indicate
that an element 5’ of the AbdB promoter, termed the Promoter Tethering Element
(PTE), is capable of selectively directing enhancers to a minimal promoter.
We plan to use biochemical and genetic techniques to identify the factors
which mediate the PTE activity and dissect its function. We will
also examine whether similar regulatory elements exist at other gene
complexes in Drosophila and mouse.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Activation of cis-regulatory
elements by non-coding intergenic RNAs
|
|
|
|
|
|
|
|
It is a curious fact that at a number
of gene complexes many cis-regulatory elements are themselves
transcribed by internal promoters including intronic enhancers in immunoglobulin
genes, regulatory regions of the β-globin locus, enhancers at the mouse
H19 gene and the Bithorax complex in Drosophila.
The functions of these non-coding RNAs are unclear. However, we
have recently characterized the extensive transcriptional program between
the AbdB and abdA genes in the Bithorax complex
of Drosophila and shown that these tightly regulated transcripts
are able to define the embryonic domains of activity for cis-elements
during early development. In our model the transcription associated
with the cis-elements facilitates the entry of large Pol II-associated
enzymatic complexes responsible for chromatin modifications that activate
cis-regulatory elements. These activated regulatory sequences
ultimately define the domains of homeotic gene expression. Our current
studies are focusing on further analysis of the function of these intergenic
RNAs.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Evolutionary conserved mechanisms
of gene regulation
|
|
|
|
|
|
|
|
The recent identification of an interacting
network of cis-acting elements at the imprinted H19/Igf2
locus in mouse, similar to the elements identified at the Bithorax
complex in Drosophila, raises the possibility that the control of
gene expression in higher eukaryotes may utilize conserved mechanisms of
action. In order to directly test this idea we have introduced defined
cis-regulatory elements from the mouse and human H19
locus into Drosophila on transgenic reporter constructs. In this assay
a conserved 1.2kb imprinting control region (ICR) found upstream of H19
acts as a potent transcriptional silencer and insulator. We hope to
analyze the mechanism of action for the ICR by examining the role of DNA
and histone modifications in Drosophila. The ultimate goal
of these experiments is to examine whether cis elements from different
organisms utilize the same epigenetic mechanisms to regulate gene expression
during embryonic development.
|
|
|
|
|
|
|
|
|
|
|
|
