Basic HTML Version
Full Abstracts – CELL DIVISION AND GROWTH CONTROL
171
141
Pre-meiotic SOLO is required for sister chromatid cohesin, chromosome segregation, synaptonemal complex assembly, and DSB repair in
Drosophila meiosis.
Rihui Yan
1
, Bruce McKee
1,2
. 1) Dept Biochem, Cell, Molec Biol, Univ Tennessee, Knoxville, TN; 2) Genome Science and Technology
Program, University of Tennessee, Knoxville, TN.
Pre-meiotic SOLO is required for sister chromatid cohesin, chromosome segregation, synaptonemal complex assembly, and DSB repair in Drosophila
meiosis Rihui Yan and Bruce D. McKee Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee
37996 Recombination between homologous chromosomes and cohesion between sister chromatids are jointly required for chromosome segregation in
meiosis in many organisms. However, the role and mechanism of cohesion in Drosophila meiosis are not well understood as yet. Mutations of solo, which
encodes a cohesion protein involved in Drosophila male meiosis, cause severe homolog and sister chromatid nondisjunction of both sex chromosomes and
autosomes in female meiosis. solo mutations also caused reduced frequencies of homologous recombination and the loss of inhibition of sister chromatid
recombination as well as delayed repair of double-stranded DNA breaks (DSB). Synaptonemal complex assembly and chromosomal localization of the
cohesin protein SMC1 are defective in solo ovaries. SOLO appears on chromosomes prior to meiosis and colocalizes with the cohesin component SMC1 and
the synaptonemal complex (SC) component C(3)G in meiosis. Moreover, SOLO physically interacts with SMC1 in vivo. SOLO induced before meiosis
completely rescued solo phenotypes, however, it does not restore solo functions when it is expressed after meiosis. Our studies demonstrate that SOLO prior
to meiosis is required for its association with meiotic cohesion protein that contains SMC1 and is required for DSB repair, homologous recombination, SC
assembly and chromosome segregation during Drosophila meiosis.
142
Control of centriole replication by centrosomin proteins.
Timothy Megraw
1
, Ling-Rong Kao
1
, Paul T. Conduit
2
, Jordan W. Raff
2
. 1) Biomedical
Sciences, Florida State University, Tallahassee, FL. USA; 2) Sir William Dunn School of Pathology, University of Oxford, Oxford, UK.
Centrosomins are conserved centrosome proteins. In Drosophila, centrosomin (Cnn) is required for PCM assembly and for the MTOC activity of mitotic
centrosomes. In humans the centrosomin
Cdk5rap2
is mutated in MCPH, a neural stem cell disease that effects brain growth. We recently reported that in
Cdk5rap2
mutant mouse cells the mitotic centrosomes have apparently normal MTOC activity but have amplified centrioles. The mechanism appears to
involve loss of centriole engagement.
Consistent with the role for Cdk5rap2 in centriole replication control, we found mutations in Drosophila
cnn
that also cause unrestricted centriole
duplication. One cluster of mutations causes centriole amplification in testis, while another mutation causes amplification in neuroblasts. Mutant
spermatocytes frequently show eight or more pairs of centrioles per cell in intact sixteen-cell cysts. In contrast to
cnn
null mutations, which severely disrupt
cytokinesis in spermatocytes, the new mutations reported here are male fertile despite the frequent assembly of multipolar spindles and spermatids with
multiple flagella. These mutations knock out the expression of one of two centrosomal isoforms of Cnn in testes. The remaining isoform is localized to
functional centrosomes. By expressing a set of rescue constructs, we show that the level of Cnn expression, rather than a specific role(s) for Cnn isoforms, is
responsible for restricting centriole replication. Therefore, loss of expression of one of the centrosomal isoforms causes unrestricted centriole replication,
which can be rescued by expression of either centrosomal isoform in early, but not late, spermatocytes.
These results show that, while Cnn is not essential for centriole replication, the control of Cnn levels is critical to restrict centriole replication to once per
cell cycle.
143
Spindle misorientation does not cause tumor-like phenotypes in the follicle cell epithelium.
Daniel T Bergstralh, Daniel St Johnston. Gurdon Inst, Univ
Cambridge, Cambridge.
The incorrect orientation of mitotic spindles has been heavily implicated in tumorigenesis in mammals. It has also been suggested to underlie tumor-like
phenotypes in the Drosophila follicle cell epithelium (FCE), a single layer of epithelial cells in which spindles are normally oriented in parallel to the place
of the epithelium. While studies in Drosophila have contributed greatly to our understanding of this process in several tissues, spindle orientation in the FCE
has not been extensively examined. In the neuorepithelium, spindles orient through interaction with adherens junctions. We show that this interaction is not
at work in the FCE. However, we demonstrate that Pins is expressed in the ovary and, as in other tissues, participates in orienting spindles in the FCE. We
further show that exogenous expression of Inscuteable, another spindle orientation factor, promotes a 90 degree reorientation of the spindle. Surprisingly,
neither the loss of Pins nor the expression of Inscuteable cause tumor-like phenotypes. Live imaging reveals that cells dividing outside the plane of the
epithelium reintegrate into the monolayer. These results indicate that although spindle orientation is under control in the FCE, the loss of that control is not
sufficient to promote loss of epithelial integrity, suggesting a checkpoint process whereby that integrity is actively monitored and maintained.
144
Endocrine hormonal effects on neoplastic tumorigenesis.
Thu H. Tran, Katherine Pfister, Adrian Halme. Department of Cell Biology, University of
Virginia School of Medicine, Charlottesville, VA.
Tumor formation is a multi-factorial process that involves contributions from both genetic mutations within tumor cells as well as inputs from surrounding
signals. In
Drosophila
, several tumor suppressor genes have been identified, enhancing our understanding of the role of autonomous gene mutations in tumor
formation. In contrast, relatively little is known in
Drosophila
about the non-autonomous effects of surrounding signals on mutant cells during
tumorigenesis. To address this, we have begun to examine the role of developmental signals in regulating tumor formation and progression. The endocrine
signals ecdysone and juvenile hormone are critical coordinators of
Drosophila
developmental transitions. Using several different neoplastic tumor models,
we have characterized the initiation of tumorigenesis in these models and observed a correlation between the timing of tumor formation in imaginal tissues
and the expression of
juvevenile hormone esterase
(
Jhe
).
Jhe
expression initiates a developmentally important transition in larval hormone signaling, where
juvenile hormone levels drop and ecdysone signaling begins to rise, eventually leading to pupation. Furthermore, we have shown that the manipulation of
larval endocrine signals alters tumor development, suggesting that the larval endocrine signals play an important role in regulating tumorigenesis. Ongoing
experiments are examining the effects of specific endocrine hormone signals on tumor formation and development, and exploring the molecular mechanisms
by which hormone signals regulate tumorigenesis.