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Poster Full Abstracts - Chromatin and Epigenetics
Poster board number is above title. The first author is the presenter
224
transvection
in vivo
. Viable heteroallelic combinations of
Top2
mutants were used to examine transvection at three classically studied loci (
yellow, white,
and
Ultrabithorax
). Transvection at
yellow
and
Ultrabithorax
lead to transcriptional activation, while mutant
zeste
1
causes pairing-dependent gene silencing
of the
white
gene. For each gene, homologous interactions between transvecting alleles were analyzed for alterations in pairing-dependent changes in
phenotype. An effect was seen at two of three loci assayed. Current studies are examining chromosome interactions in larval tissues using fluorescent
in situ
hybridization. Data obtained from these studies will determine whether
Top2
is required for homolog interactions in somatic cells.
341B
HP1b is a non-essential protein enriched at TSSs that positively affects transcription.
Nicole C. Riddle, Artyom A. Alekseyenko, Tingting Gu,
Youngsook L. Jung, Aki Minoda, Michael Y. Tolstorukov, Mitzi I. Kuroda, Vincenzo Pirrotta, Peter J. Park, Sarah C. R. Elgin, Gary H. Karpen. Drosophila
modENCODE Chromatin Group.
In
Drosophila melanogaster
, the Heterochromatin Protein 1 (HP1) family of proteins is represented by five different proteins, HP1a, HP1b, HP1c, rhino
(HP1d), and HP1e. HP1a was first to be identified due to its strong association with the heterochromatic fraction of the Drosophila genome. HP1a is
composed of two conserved protein domains, the chromo domain and the chromo-shadow domain, connected by a hinge domain. This basic structure is
common to all HP1 proteins; however, the N- and C-terminal “tails” as well as the hinge domain vary in size. While the expression of
rhino
and
HP1e
are
restricted mainly to the germline,
Su(var)205[HP1a]
,
HP1b
, and
HP1c
are expressed ubiquitously. However, they differ in their genomic distribution, HP1a
associating mainly with heterochromatin, HP1c with euchromatin, and HP1b localizing to both. Here, we report the generation of
HP1b
mutants and a
detailed, comparative analysis of the genome-wide localization of HP1a, HP1b, and HP1c. We find that
HP1b
is a non-essential gene, with mutants viable,
fertile, and lacking morphological defects.
HP1b
mutations enhance variegation of an
hsp70-white
reporter. HP1b is found primarily associated with
transcription start sites, similar to HP1c. In S2 cells, approximately 6000 genes are associated each with HP1b and HP1c. Of these, approximately 5000
genes are enriched for both HP1 family members. Genes targeted by HP1b and HP1c occur both in euchromatin and heterochromatin and are enriched for
GO terms related to “development” and “regulation”. Interestingly, approximately 1300 of these genes also associate with HP1a, indicating that all three
non-germline HP1 family members occur together at a significant number of sites. On-going experiments explore how mutations in HP1 family members
influence the localization patterns of the other paralogs and will shed light on the mechanisms regulating the genomic enrichment patterns.
342C
Investigating the impact of an invading B chromosome on nuclear dynamics in N. vitripennis.
Megan Swim, Patrick M. Ferree. Keck Science
Department, Scripps College, 925 N. Mills Ave. Claremont, CA.
Supernumerary B chromosomes are nonessential extra chromosomes present in numerous plant and animal species. Some B chromosomes are capable of
imposing strong positive or negative effects. An extreme example this is the Paternal Sex Ratio (PSR) chromosome in the jewel wasp Nasonia vitripennis.
PSR is transmitted through the sperm at a frequency near 100%. PSR is believed to imprint the paternal chromatin during spermatogenesis such that it
becomes hyper-condensed and fails to resolve into distinct chromosomes during the first embryonic mitosis. Nasonia, like all hymenopteran insects, exhibits
haplodiploid reproduction, in which females develop as diploid individuals from fertilized eggs while males develop as haploids from unfertilized eggs. By
destroying the paternal chromosomes, PSR converts fertilized embryos that should become females into haploid males, thus selfishly facilitating its own
propagation. Two vital questions regarding PSR transmission are: (i) what is the nature of the epigenetic modification that PSR inflicts upon the paternal
chromatin and how does this occur? And (ii) how does PSR evade this lethal effect despite its close association with paternal chromatin during
spermatogenesis. To address these questions, we engineered several FISH probes that have allowed us to follow PSR during early development. We found
that PSR localizes to the outer periphery of the paternal pronucleus in a position that is often directly adjacent to the maternal pronucleus. Additionally, PSR
escapes the doomed paternal chromatin during anaphase of the first mitosis in order to associate with the viable female chromosomes. To investigate the
localization of PSR at the periphery of the paternal pronucleus, we used FISH to examine PSR in developing sperm. Intriguingly, we discovered that PSR
localizes to the extreme apical tip of the elongated sperm nucleus at near perfect frequencies. PSR also appears to reorder the autosomes within the nucleus.
These findings provide new and exciting insights into how selfish genetic elements can utilize host nuclear processes for their survival.
343A
Characterizing Chromosome Territory Formation in Drosophila Primary Spermatocytes.
Sheng (Jimmy) Tang
1
, Tom Hartl
1,2
, Matthew Scott
1,2
. 1)
Stanford University, Stanford, CA; 2) Stanford University School of Medicine, Stanford, CA.
In the nuclei of interphase cells, chromosomes occupy distinct, non-overlapping domains called chromosome territories (CTs). Proper territory formation is
necessary for the expression and regulation of many genes. Aberrant CTs are often seen in the cells of apoptotic or cancerous tissues. In addition, despite
having different numbers of chromosomes, many species ranging from flies to mammals possess cells where CTs can be observed. In the nuclei of primary
spermatocytes of Drosophila, the three major chromosomes form three distinct, triametrically opposed CTs. Using nuclear DNA staining and confocal
microscopy, we have developed a system to qualitatively and quantitatively characterize CT formation within these cells. We have found that in
spermatocytes where the second and third chromosomes are fused at a single centromere, the two fused chromosomes form two distinct territories. This
finding suggests that CT formation is chromosome-specific, such that each chromosome recognizes "self" and "non-self" chromatin during territory
compaction. Immediate studies will focus on using translocation constructs to determine whether CT formation is specific to chromatin at the sub-
chromosomal level. In addition, using a germline-specific GAL4 driver, we have initiated an RNAi screen to search for specific protein factors that are
responsible the formation or maintenance of CTs in spermatocytes.
344B
Telomere dynamics and organization in early embryonic development.
Natalia Wesolowska
1,2
, Yikang Rong
1
. 1) Lab of Biochemistry and Molecular
Biology, National Institutes of Health, Bethesda, MD; 2) NIH Graduate Partnership Program with the CMDB Program, Johns Hopkins University,
Baltimore, Bethesda.
Telomeres are specialized structures that delineate the ends of linear chromosomes. When their function is compromised, natural ends resemble broken
DNA and can be subjected to repair, resulting in chromosomal fusions and genomic instability. We would like to address a major aspect of nuclear dynamics