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Poster Full Abstracts - Cell Death
Poster board number is above title. The first author is the presenter
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rescued by co-expression of pan caspase inhibitor p35 or DIAP1. Hence, we investigated the role of Dronc in Hippo mediated cell death, as Dronc activity is
resistant to p35 and not affected by changes in DIAP1 levels. We found that Hippo genetically interacts with Dronc and requires dronc to induce cell death.
Our data suggests Hippo pathway can regulate cell death through the RHG proteins and via Dronc. Dronc along with its binding partner Dark can suppress
the over-growth induced by over-expression of Yki, suggesting that normally Hippo pathway needs to restrict Dronc activity to maintain tissue homeostasis.
Consistent with this idea, we found the Hippo pathway transcriptionally regulates dronc. Loss of dronc results in cell survival and dronc mutant cells
proliferate faster than their wild-type twin spots. Here we present dronc (a gene required for cell competition and for caspase-mediated cell death) as a novel
target of Hippo signaling.
319A
A ciliopathy model to test the regenerative capacity of primary cilia and to screen small molecule therapies.
Jieyan Chen, Timothy Megraw.
Biomedical Sciences, Florida State University, Tallahassee, FL.
The primary cilium is found on nearly all cells and it plays critical roles in development, cell signaling, and environmental sensing. There are no treatments
for ciliopathies in humans. A treatment, if possible, will require that cilia have the potential to regenerate. It is not known if centrioles or cilia can regenerate
in differentiated cells. Flies have primary cilia only on mechanosensory, chemosensory and visual system neurons. Orthologs for most ciliopathy genes exist
in Drosophila. Loss of function for some of these genes results in an uncoordinated phenotype due to loss of mechanosensation. Inducible expression of
hairpin constructs that elicit RNA interference (RNAi) using the “GAL4 system” with a temperature-sensitive GAL80 inhibitor of GAL4 permits induction
and termination of RNAi during development or in adults. We have performed an initial RNAi screen of candidate proteins represent three classes of cilium
assembly or function: 1) centriole biogenesis proteins, 2) cilium assembly proteins, and 3) ciliary membrane ion channels. Among 35 genes screened, 11
show a severe “uncoordinated” phenotype upon RNAi, 4 of which are orthologs of genes associated with ciliopathies in humans. We are now testing
regenerative capacity of cilia upon restoration of gene expression in adult by analyzing cilium functions with quantitative locomotive assay, combined with
immunofluorescence and electron microscopy ultrastructural imaging of cilia and basal bodies in adult neurons. We will also complement the RNAi
approach with inducing transgenes in null mutant backgrounds to assay cilium regeneration in adult neurons. Meanwhile, we select two candidate ciliopathy
gene models to score cilium function recovery by assaying locomotive behavior “rescue” in RNAi knockdown flies, following treatment with a library of
chemicals, to screen for potential drugs that relieve the developmental and/or adult-onset ciliopathies. With this ciliopathy model, we will define the
regenerative plasticity of centrioles and cilia in vivo, and discover potential drugs for the treatment of ciliopathies.
320B
Heterochromatin-mediated pairing and segregation of achiasmate chromosomes depends on HP1.
Christopher C. Giauque, Justin J. Gaudet, Sharon E.
Bickel. Department of Biological Sciences, Dartmouth College, Hanover, NH.
Meiotic nondisjunction is one of the leading causes of human infertility and birth defects, including Down Syndrome, but little is known about its
underlying causes. Accurate segregation of meiotic homologous chromosomes is usually dependent on the establishment of chiasmata between homologues
during recombination. However, in Drosophila oocytes, although
4th
chromosomes are always achiasmate and
X
chromosomes fail to recombine 6-12% of
the time, these chromosomes still segregate with high fidelity. Work from a number of labs has demonstrated that proper segregation of achiasmate
homologues depends on the physical association of their centromere-proximal heterochromatin, but the role of heterochromatin proteins in this process has
not been investigated. Our lab has previously reported that weak mutations in the meiotic cohesion protein ORD disrupt heterochromatin-mediated pairing of
achiasmate chromosomes. Here, we explore the role of the heterochromatin protein HP1 (encoded by the
Su(var)205
gene) in the pairing and segregation of
achiasmate chromosomes. HP1 is a highly conserved essential gene product required for normal heterochromatin formation. In addition, HP1 has been
implicated in recruiting the cohesin complex to pericentric heterochromatin. Using a Gal4/UAS RNAi strategy, we reduced HP1 in the female germ line and
used FISH to monitor heterochromatin pairing of the obligate achiasmate
FM7/X
chromosome pair. We find that reduction of HP1 during meiotic prophase
disrupts heterochromatin mediated pairing of the
FM7/X
homologues. In addition, in
Su(var)205
heterozygous oocytes, we observe a small but significant
increase in nondisjunction of the
FM7/X
chromosome pair. These data indicate that wild-type levels of HP1 protein are required for normal pairing and
segregation of achiasmate chromosomes. We are currently exploring the possibility that reduction of HP1 disrupts heterochromatin-mediated pairing of
homologues because recruitment of cohesion proteins to pericentric regions is decreased.
321C
Nondisjunctional segregation in
Drosophila
female meiosis I is preceded by homolog malorientation at metaphase arrest.
William Gilliland, Shane
Gillies, Khateriaa Pyrtel, Wonbeom Paik, Nneka Wallace. Department of Biological Sciences, DePaul University, Chicago, IL.
The recent discovery that chromosome congression does occur in the first meiotic division in
Drosophila
female meiosis requires reexamination of what
goes wrong to cause nondisjunctional segregation. We have found that several mutants that cause high rates of nondisjunction are still competent to
complete congression. One possibility is that congression errors result in metaphase arrested oocytes with maloriented homologs in the congressed
karyosome. If this is the case, then chromosome malorientation rates should be equal to nondisjunction rates. To test this hypothesis we assayed an
ald
allelic series for both genetic nondisjunction rates as well as homolog coorientation rates using combined immunofluorescence plus chromosome-specific
FISH. These two rates are highly correlated, indicating that events during congression are responsible for chromosome nondisjunction during meiosis I.
322A
Chromosome axis proteins regulate synapsis initiation in Drosophila oocytes.
Kathryn Landy, Mercedes Gyruicza, Kim McKim. Waksman Institute of
Microbiology, Rutgers University, Piscataway, NJ.
Accurate chromosome segregation is crucial for the proper completion of meiosis and involves multiple intricate processes, including synapsis, which
tethers homologous chromosomes, and cohesion, which tethers sister chromatids. Synapsis is the process of assembling the synaptonemal complex (SC), a
proteinaceous structure that joins homologs along the chromosome axis. The axis runs along the length of each chromosome and is composed of several
proteins, including the SC protein C(2)M, ORD and cohesion proteins. We have found that these chromosome axis proteins regulate three distinct stages of
synapsis initiation: first, at the centromeres, second at 6-8 ORD-dependent euchromatic sites, and third at 15 to 18 additional C(2)M-dependent euchromatic