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Poster Full Abstracts - Gametogenesis and Organogenesis
Poster board number is above title. The first author is the presenter
278
546C
The Misshapen kinase negatively regulates integrins to promote follicle cell migration during egg chamber development.
Lindsay K. Lewellyn, Sally
Horne-Badovinac. Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL.
Collective cell migration is critical to the proper formation of tissues and organs during development. These complex cell movements are orchestrated by
the actin cytoskeleton and its dynamic interaction with the extracellular matrix (ECM) through transmembrane receptors such as the integrins. The egg
chamber is a simple organ-like structure within the Drosophila ovary that is composed of a single oocyte and 15 nurse cells, surrounded by an epithelial layer
of follicle cells. This epithelium undergoes a collective migration perpendicular to the egg chamber’s A-P axis, an event that helps to transform this initially
spherical structure into an elongated egg. Through a forward genetic screen, we have identified the Ste20-like kinase Misshapen (Msn) as a key regulator of
egg chamber elongation. Live imaging revealed that loss of Msn leads to a cell autonomous defect in follicle cell migration.
msn
mutant cells show higher
levels of integrins at the basal surface, and a disruption of ECM structure. Instead of being polarized around the circumference of the egg chamber, an
arrangement that is believed to limit growth to the A-P axis, Collagen IV filaments are stuck around the edges of
msn
mutant cells. These observations
suggest that the mutant cells are more tightly adhered to the underlying ECM, and that Msn negatively regulates integrin-based adhesion. Consistent with
this model, reducing integrin levels by introducing one
myospheroid
mutant allele, partially rescues follicle cell migration and egg chamber shape in the
msn-RNAi
condition. Finally, observation of a Msn-YFP protein trap revealed that Msn is planar polarized at the basal surface, where it is enriched at the
back of the migrating follicle cells. From these data, we propose that Msn negatively regulates integrins at the back of each follicle cell to promote collective
cell migration.
547A
MIPP regulates tracheal morphogenesis through cell intercalation.
Yim Ling Cheng, Deborah Andrew. Cell Biology, Johns Hopkins School of
Medicine, Baltimore, MD.
The
Drosophila
trachea is among the best model systems for studying tubular morphogenesis, an important process in the development of many organs.
The major transcription factor regulating trachea formation is Trachealess (Trh), a basic HLH protein expressed in trachea from early development. We
identified
mipp1
as one of the downstream targets of Trh in a global
in situ
hybridization screen.
mipp1
encodes a dual substrate specificity multiple inositol
polyphosphate phosphatase that can dephosphorylate higher inositol polyphosphates to the Ca++ second messenger IP3 and dephosphorylate 2,3-
bisphosphoglycerate to 2-phosphoglycerate. Although the MIPPs are very highly conserved, their biological function remains poorly understood.
Drosophila
encodes two
mipp
genes:
mipp1
and
mipp2
. To learn the role of
mipp1
and
mipp2
in tracheal development, we generated a knockout of
mipp1
by
homologous recombination and obtained available
mipp2
mutant lines. Double
mipp1 mipp2
mutants have defects in dorsal trunk elongation, dorsal branch
fusion and ganglionic branch migration that are more severe than observed with either single
mipp
mutant.
mipp2
is ubiquitously expressed, but
mipp1
is
expressed specifically in the trachea. Initially, mipp1 is expressed in all tracheal cells but is downregulated by stage 14 in tracheal cells that do not undergo
the process of cell intercalation to elongate (dorsal trunk and transverse connective). Based on the
mipp1
expression pattern, we speculated that the MIPPs
are involved in promoting tracheal cell intercalation, which would explain the wide range of tracheal defects observed in the mipp mutants. Indeed, we
observed both delays and failures in tracheal intercalation in
mipp1
KO
. To further characterize the roles of MIPPs and their substrates in cell intercalation, we
are asking if the tracheal phenotypes can be rescued by enzyme-dead MIPP1 as well as the wild-type MIPP1, if
mipp1
is regulated by Spalt, the major
negative regulator of cell intercalation in the trachea, and if the MIPPs affect the proteins known to be involved in tracheal cell intercalation.
548B
Tracheal Development in
Drosophila
Visual System.
Wei-Chen Chu
1,2
, Yuan-Ming Lee
1,3
, Yi Henry Sun
1,2,3
. 1) Institute of Molecular Biology, Academia
Sinica, Taipei, Taiwan; 2) Graduate Institute of Life Sciences, National Defense Medical Center, Taipei,Taiwan; 3) Department of Life Sciences and
Institute of Genome Sciences, National Yang Ming University, Taipei, Taiwan.
Drosophila
eye is a highly specialized neuronal system, and its neuronal activity should require lots of oxygen. The oxygen can be transported by trachea
in insects. However, the distribution and development process of trachea in the
Drosophila
visual system have not been studied. To address this issue, we
study the adult tracheal pattern, tracheal development process and its biological role in eye. These may provide a link between visual system and respiratory
system. We have determined the retinal tracheal pattern and established the 3D model. And we also found the critical developmental stage for the trachea in
Drosophila
visual system. It has been shown that branching morphogenesis of the
Drosophila
tracheal system in embryo depends on the FGFR/FGF
signaling pathway. Tracheal cells specifically express the FGFR (Breathless, Btl) that receives the FGF ligand Branchless (Bnl) signal. Bnl acts as a
guidance molecule controlling tracheal cell migration. We have also found that
btl/bnl
signaling affected tracheal growth in eye. The flies with less retinal
trachea can be created by manipulation of
btl
in trachea or
bnl
in eye. These flies show weaker ERG amplitude and age-dependent degeneration. It suggests
that the trachea in the
Drosophila
eye is important for normal eye function. We speculate that as the eye grows in size, hypoxia will develop and induce
tracheal ingrowth. This system may be used to study the role of hypoxia response in eye development, perhaps similar to mammalian angiogenesis.
549C
The role of Cad99C in apical membrane dynamics.
Se-Yeon Chung, Deborah Andrew. Dept Cell Biol, Johns Hopkins Univ, Baltimore, MD.
Usher Syndrome (USH) is the most frequent cause of hereditary deaf-blindness in humans. The gene products of nine USH disease genes have been
identified so far, most of which are highly conserved from flies to humans. Cadherin99C (Cad99C), the Drosophila orthologue of human Usher Cadherin
PCDH15, regulates the length of microvilli in ovarian follicle cells. Cad99C is also strongly expressed in embryonic tubular organs including the salivary
gland (SG) and trachea. The apical membranes of these tissues undergo dynamic changes during tube morphogenesis, suggesting a potential role for Cad99C
in apical membrane dynamics. Although zygotic loss of
Cad99C
does not result in overt SG defects (perhaps because of maternal supplies), high-level
expression of Cad99C results in profound changes in the polarity and shape of SG epithelial cells. Cad99C overexpression in the SG results in
mislocalization of apical-basal markers such as SAS and α-Spec, and the epithelial cells become round, rather than maintaining their typical columnar shape.
Apical actin and tubulin are also disorganized and, within each cell, is a small region of Cad99C staining of what appear to be elongated microvilli. Loss of
moe
, the single Drosophila member of Ezrin/Radixin/Moesin family of actin-binding proteins suppresses the Cad99C overexpression phenotype, suggesting
a link between the actin cytoskeleton and Cad99C activity. We are currently exploring phenotypes associated with both maternal and zygotic loss of
Cad99C