Basic HTML Version
Poster Full Abstracts - Regulation of Gene Expression
Poster board number is above title. The first author is the presenter
341
pathway, the transcriptional coactivator Yorkie (Yki), is an essential mediator of Hippo-regulated proliferation and is required for cell survival and
proliferation in all imaginal discs. Yki lacks a DNA binding domain and must partner with sequence-specific DNA binding proteins in the nucleus to
regulate gene expression. Two well-characterized Yki binding partners are the developmental regulators Scalloped (Sd) and Homothorax (Hth), which are
required for cell survival and proliferation in the wing and eye, respectively. To better understand tissue specific gene regulation by these transcription
factors at the downstream end of the Hippo pathway, we performed genome-wide chromatin immunoprecipiatation experiments for each factor in both the
wing and eye-antenna imaginal discs. Strong, tissue-specific binding patterns are observed for Sd and Hth, while Yki binding is remarkably consistent across
these two tissues. Importantly, binding events common to the eye and wing are also present for Sd and Hth; these general binding events are associated with
genes regulating cell proliferation and other "housekeeping" functions, and can account for the vast majority of Yki binding. Tissue-specific binding events
for Sd and Hth are consistent with developmental roles in the given tissue, and have led to characterization of adjacent, but separate, Sd- and Hth-dependent
wing and eye enhancers for the
bantam
microRNA. Overall these results suggest that the transcription factors Sd and Hth use distinct binding strategies —
one general and associated with Hippo signaling, the other tissue-specific and associated with developmental patterning — to regulate the distinct gene sets
during development.
784A
Sculpting the insect abdomen: molecular characterization of sexually dimorphic regulation of Wingless by Abd-B and Doublesex.
Wei Wang, John
Yoder. Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL.
Diverse abdominal morphologies found throughout the order Diptera present an attractive system for investigating developmental and evolutionary
mechanisms underlying morphological novelty. One such trait, shared by all Cyclorrhaphan diptera, is adult abdominal segment number; males possess
fewer segments than females. The Hox protein Abdominal-B (Abd-B) and products of the sex-determination gene Doublesex (Dsx) coordinately regulate
reduction of the posterior-most adult male abdominal segments. We have shown this reduction is principally controlled through male-specific transcriptional
repression of the morphogen Wingless (Wg) in the posterior-most abdominal segment A7. To investigate whether Abd-B and Dsx directly regulate Wg
expression we have performed a systematic molecular screen to identify cis-regulatory elements (CREs) governing Wg expression. We have identified two
non-overlapping genomic fragments each capable of driving expression of a reporter gene in patterns reflecting endogenous abdominal Wg protein.
Expression driven by both fragments responds to Abd-B and Dsx expression levels suggesting that a minimum of two distinct CREs regulate Wg expression
in the Drosophila pupal abdomen. We are currently characterizing smaller sub-clones of these fragments to identify minimal sequences necessary for correct
spatial control of Wg abdominal expression. In order to investigate direct regulation of Wg abdominal expression by Abd-B and Dsx these minimal CREs
will be subjected to electrophoretic mobility shift experiments and mutational analyses. Characterization of Abd-B and Dsx as direct regulators of Wg
expression will provide the necessary genetic context in which to explore the hypothesis that the evolution of abdominal segment number within the higher
diptera (Cyclorrhapha) occurred through cis-regulatory changes at the Wg locus.
785B
Disentangling the Sources of Species-Specific Gene Expression Patterns in Drosophila Embryos.
Zeba Wunderlich
1
, Meghan Bragdon
1
, Kelly
Eckenrode
1
, Charless Fowlkes
2
, Angela DePace
1
. 1) Systems Biology, Harvard Medical School, Boston, MA; 2) Computer Science, University of California,
Irvine, CA.
Phenotypic divergence in populations and between species has been traced to changes in gene expression, but we cannot yet predict how sequence changes
affect regulatory sequence function. To investigate the quantitative connection between regulatory sequence and function, we experimentally and
computationally characterized the expression driven by several sets of orthologous
cis
-regulatory elements (CREs) in blastoderm-stage
Drosophila
embryos.
Using quantitative 3D cellular resolution imaging techniques, we created atlases of gene expression for key transcription factors (TFs) in the anterior-
posterior patterning network in several
Drosophila
species. To disentangle contributions of different sources to expression divergence, we created a cell-by-
cell model to relate the levels of the input TFs to the endogenous expression pattern directed by each CRE. To assess the degree of regulatory function
conservation of orthologous CREs, we fit the model’s parameters in one species and apply them to the other species. We find that regulatory function
conservation drops off with phylogenetic distance, but the majority of expression divergence between species is explained by the differences in expression
patterns of input TFs. To investigate the contribution of sequence changes in CREs to expression divergence, we made transgenic lines with orthologous
CREs driving a reporter in
D. melanogaster
. We use a simple measure of sequence function to fit the quantitative differences between these lines. In closely
related species, we can explain virtually all the observed endogenous expression differences as a combination of changes in input TF expression patterns and
CRE sequence change, while in more distantly related species, there is evidence for compensatory mutations outside annotated CREs. We discuss how to
generalize this approach to measure how sequence divergence effects regulatory function and implications for the evolution of gene regulation.
786C
Regulation of the Sex-determination Transcription Factor Doublesex by the Hox protein Abdominal-B.
Shun Yan
1
, Wei Wang
1
, Michelle Arbeitman
2
,
John H.Yoder
1
. 1) University of Alabama, Tuscaloosa, AL; 2) College of Medicine, The Florida State University, Tallahassee, FL 32306.
Posterior abdomen of adult Drosophila melanogaster displays several sexually dimorphic traits including male-specific pigmentation as well as sex-
specific segment morphology and segment number. Two principle transcription factors that control these abdominal morphologies are the Hox protein
Abdominal-B (Abd-B) and products of the sex-determination gene Doublesex (Dsx). These proteins function cooperatively to confer sex-specific repression
or activation upon downstream target genes including bric-a-brac (bab) and Wingless (Wg). However, little is known about the interaction between these key
transcriptional regulators. Expression studies have shown that Dsx transcription is temporally and spatially dynamic throughout development. We therefore
investigated Dsx expression during early pupation when Dsx and Abd-B function cooperatively to reduce segment number in male flies. We found that Dsx
is transcriptionally regulated downstream of Abd-B. To investigate whether this regulation is direct we have screened genomic fragments from the Dsx locus
for the ability to drive reporter gene expression in the developing pupal abdomen. We have identified two non-overlapping fragments each containing Abd-B
responsive Dsx abdominal enhancers. Together these fragments recapitulate Dsx abdominal expression. Analyses of the regulation of these elements have
revealed complex genetic regulation beyond the Hox input.