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Poster Full Abstracts - Gametogenesis and Organogenesis
Poster board number is above title. The first author is the presenter
283
Montreal, Montreal, QC, Canada.
Phosphoinositides are lipids that provide a molecular link for membrane interactions with cellular machinery. Phosphatidylinositol (PI) 4-kinases (PI4Ks)
catalyze the conversion of PI to PI 4-phosphate (PI4P), a cellular effector that recruits trafficking proteins and serves as a precursor to other essential
phosphoinositides. To investigate the function of phosphoinositides during development, we generated a deletion in the gene encoding the
Drosophila
melanogaster
type IIIα PI4K (PI4KIIIα). We find that
PI4KIIIα
is required for production of plasma membrane phosphoinositides that are crucial for
membrane trafficking, actin organization and cell polarity during oogenesis. Female germ cells mutant for
PI4KIIIα
lose cortical integrity and are impaired
in activation of the PI 4,5-bisphosphate [PI(4,5)P
2
]-binding cytoskeletal-membrane crosslinker Moesin. Titration of PI(4,5)P
2
using the pleckstrin homology
domain of phospholipase C partially recapitulates
PI4KIIIα
phenotypes, indicating that PI(4,5)P
2
is the main phosphoinositide effector downstream of
PI4KIIIα. These effects are specific to
PI4KIIIα
, as they are not produced in egg chambers mutant for either or both of the two remaining PI4Ks,
PI4KIIIβ/fwd
and
PI4KII
. Instead,
fwd
and
PI4KII
mutant germ cells exhibit altered Golgi distribution, whereas this is unaffected in
PI4KIIIα
mutant cells.
Furthermore, membrane defects in
fwd
,
PI4KII
, and
fwd PI4KII
double mutant cells appears morphologically distinct from that in
PI4KIIIα
cells. Thus, as in
yeast and mammalian cells, different
Drosophila
PI4Ks appear to have organelle-specific roles and produce functionally distinct pools of PI4P.
567C
The role of follicle cells in developmental nurse cell death and clearance in late oogenesis.
Allison Timmons, Jon Iker Etchegaray, Claire Schenkel, Kim
McCall. Biology, Boston University, Boston, MA.
Programmed cell death (PCD) is an essential process in animal development and tissue homeostasis which ensures that aged, damaged, or excess cells are
eliminated. In the
Drosophila
ovary, PCD occurs as a normal part of development. During late oogenesis, germline derived nurse cells provide nutrients,
proteins, mRNAs, and organelles for the developing oocyte. Beginning in stage 11, the nurse cells transfer their contents into the oocyte and undergo PCD.
Interestingly, disruption of apoptosis or autophagy only partially inhibits PCD of the nurse cells, indicating that other mechanisms are contributing to the
process. One possibility is that the follicle cells are contributing to the death and/or clearance of the nurse cells in late oogenesis. Using
UAS-mCD8-GFP
specifically expressed in the follicle cells, follicle cell membranes surround the nurse cells beginning in stage 10, and by stage 12 the follicle cells
completely encompass each nurse cell. Disruption of
draper
or
basket
in the follicle cells results in a persisting nurse cell nuclei phenotype in late oogenesis,
suggesting that these nurse cells are not dying or not being cleared properly. Furthermore,
puclacZ
expression indicates that JNK signaling is activated in the
follicle cells during late oogenesis which previously has been attributed to the well known role for JNK in dorsal appendage formation. We have observed
both
puclacZ
and Draper expression in the follicle cells that directly surround the nurse cells during PCD in late oogenesis. We hypothesize that in addition
to dorsal appendage formation, JNK signaling in the follicle cells contributes to the death and clearance of the nurse cells. We also hypothesize that Draper
and JNK in the follicle cells are interacting to promote the developmental PCD and clearance of nurse cells in late oogenesis. Further investigations are
underway to characterize the involvement of the follicle cells in developmental nurse cell death.
568A
The bHLH protein, Sage, provides tissue specificity to FoxA/Fork head.
Rebecca M. Fox, Aria Vaishnavi, Rika Maruyama, Deborah J. Andrew. Dept
Cell Biol, Johns Hopkins Univ, Baltimore, MD.
Tissue morphogenesis is coordinated by the actions of transcription factors. In the salivary gland (SG), the homeotic genes
Sex combs reduced (Scr)
,
homothorax (hth)
, and
extradenticle (exd)
initiate SG specification by activating expression of the transcription factors Fork head (Fkh), Sage, CrebA and
Huckebein (Hkb). Fkh is required for SG invagination as well as for maintaining its own expression and expression of many other SG genes. CrebA
regulates the high-level secretory capacity required for SG function, and Hkb is required for SG tube elongation. Sage is the only SG specific transcription
factor and has been implicated in the maintenance of the SG lumen through its regulation of two prolyl-4 hydroxylase genes, PH4αSG1 and PH4αSG2. We
have generated Sage null mutants and discovered that Sage is required for SG survival in late embryos. To identify Sage target genes, we performed
microarray analyses and discovered that Sage regulates genes encoding proteins secreted from the SG and the enzymes that modify these secreted products.
Interestingly, whereas overexpression of either Fkh or Sage alone is not sufficient to induce ectopic SG target gene expression, coexpression of Fkh and
Sage can activate SG gene expression in multiple ectopic locations. Consistent with this finding, we have discovered that Sage and Fkh protein localize to
the same sites on SG polytene chromosomes, indicating that the two proteins act directly on the same sets of target genes. Thus, we have identified a SG
specific transcripton factor, Sage, that functions with the FoxA factor, Fkh, to activate SG specific gene expression. These findings suggest a paradigm
wherein a bHLH factor with very limited expression acts with the more widely expressed FoxA transcription factor to provide tissue specificity.
569B
oak gall and conjoined alter Branching Morphogenesis and Tube Formation in the Drosophila Tracheal System.
Deanne M. Francis, Amin Ghabrial.
Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA.
The Drosophila tracheal system is derived from 10 pairs of epithelial sacs, each comprised of approximately 80 cells. In response to an FGF
(Branchless/Bnl) cue, new branches bud from the tracheal sacs. Each new branch migrates towards the source of the FGF cue, led by one or more "tip cells."
Most, if not all, tracheal cells are capable of becoming tip cells, but tip cell number is restricted by a competition-based mechanism. We have identified 2
mutants, oak gall and conjoined, which confer a tip cell bias in genetic mosaic experiments. In addition, both oak gall and conjoined mutant cells have a
rounded cell morphology, and terminal cells mutant for either gene show specific tube defects in the area between the terminal cell-stalk cell junction and the
terminal cell nucleus. We have determined that oak gall and conjoined encode the E and G subunits of the vacuolar ATPase complex, respectively. Further
experiments will identify the mechanism by which the vacuolar ATPase plays a role in tip cell specification, terminal cell morphology and tracheal
tubulogenesis.
570C
The role of the exocyst in subcellular morphogenesis.
Tiffani A. Jones, Mark M. Metzstein. Human Gen, Univ Utah, Salt Lake City, UT.
Branching morphogenesis and tubulogenesis are important morphological processes required for proper development of many organs and individual cells.
However, the molecular mechanisms controlling these processes remain mostly unknown. To identify components required for branching and tubulogenesis,