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Poster Full Abstracts - Stem Cells
Poster board number is above title. The first author is the presenter
356
unknown. We are using the development of the ovary in the fruit fly Drosophila melanogaster to study organ formation. During the larval growth period,
ecdysone signaling coordinates the proliferation and differentiation of two distinct cell populations: primordial germ cells (PGCs), the precursors for germ
line stem cells (GSCs), and the precursors for their somatic niches. We demonstrate that Activin signaling is also required for soma-germ line coordination
by modulating the ovarian response to ecdysone. Removing the type I Activin receptor, Baboon (Babo), or its down-stream effector Smox from the ovarian
soma by RNAi results in significantly smaller gonads, with underdeveloped niches. Conversely, somatic over-expression of the constitutively active receptor
(Babo*), results in larger ovaries, and precocious niche formation. PGCs also differentiate precociously in Babo* ovaries. Babo* expressing ovaries
resemble ovaries in which the Ecdysone pathway is precociously activated. These gonads also demonstrate early precocious expression of Broad-Z1
isoform, a major target of the Ecdysone pathway. Similarly, removal of Smox or Babo from the ovarian soma by RNAi results in a significant decrease in
Broad-Z1. Our results suggest a role for Activin signaling in niche formation and PGC differentiation. They also demonstrate how temporal cues might
converge with growth and differentiation cues to coordinate these two processes.
840C
Characterization of the Follicle Stem Cell Niche.
Pankaj G. Sahai-Hernandez, Todd G Nystul. Anatomy Dept., UCSF, san Francisco, CA.
Stem cells are responsible for maintaining different tissue types in a multicelullar organism. Stem cells are located in a specialized microenvironment
termed a niche, which provides the appropriate signals for homeostasis. The follicle stem cells (FSCs) in the Drosophila ovary have been an informative
model for investigating epithelial stem cell biology in vivo. Previous studies have identified several signaling pathways, including wingless, BMP and
hedgehog, as well as cell adhesion complexes such as adherens junctions and integrins that are necessary for FSC maintenance. However, little is known
about whether there is a cellular component to the FSC niche. FSCs directly contact the neighboring escort cells, a stromal cell population that regulates the
first stages of germ cell development. FSCs must coordinate with escort cells and germ cells to ensure that new follicle cells are produced at the proper time
and place, but it is unclear what role escort cells play in FSC niche function. To better understand the cellular architecture of the FSC niche, we characterized
the shape and position of escort cells in the FSC niche region and investigated the role that these cells play in the production of niche signals. Our results
suggest that the FSC niche receives signals from several sources and must be frequently remodeled to accommodate the passage of germ cell cysts through
the germarium.
841A
magu is required for germline stem cell self-renewal through BMP signaling in the Drosophila testis.
Qi Zheng
2,3
, Yiwen Wang
1
, Eric Vargas
1
, Stephen
DiNardo
1,3
. 1) Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA; 2) Department
of Biology, School of Arts and Sciences, University of Pennsylvania, Philadelphia, PA; 3) Penn Institute for Regenerative Medicine, University of
Pennsylvania, Philadelphia, PA.
Understanding how stem cells are maintained in their microenvironment (the niche) is vital for their application in regenerative medicine. Studies of
Drosophila male germline stem cells (GSCs) have served as a paradigm in niche-stem cell biology. It is known that the BMP and JAK-STAT pathways are
necessary for the maintenance of GSCs in the testis (Kawase et al., 2004; Kiger et al., 2001; Schulz et al., 2004; Shivdasani and Ingham, 2003; Tulina and
Matunis, 2001). However, our recent work strongly suggests that BMP signaling is the primary pathway leading to GSC self-renewal (Leatherman and
DiNardo, 2010). Here we show that magu controls GSC maintenance by modulating the BMP pathway. We found that magu was specifically expressed
from hub cells, and accumulated at the testis tip. Testes from magu mutants exhibited a reduced number of GSCs, yet maintained a normal population of
somatic stem cells and hub cells. Additionally, BMP pathway activity was reduced, whereas JAK-STAT activation was retained in mutant testes. Finally,
GSC loss caused by the magu mutation could be suppressed by overactivating the BMP pathway in the germline.
842B
The centrosome positioning checkpoint monitors centrosome interaction with cortical Bazooka.
Mayu Inaba
1,2
, Yukiko Yamashita
1,2
. 1) Center for
stem cell biology, Life Sciences Institute, University of Michigan, Ann Arbor, MI; 2) Department of Cell and Developmental Biology, School of Medicine,
University of Michigan.
Asymmetric cell division is widely utilized by many adult stem cells to balance self-renewal and generation of differentiated, short-lived cells. Mitotic
spindle orientation relative to the surrounding tissue is a strategy utilized by many adult stem cells to divide asymmetrically. We recently demonstrated that
GSCs with misoriented centrosomes do not enter mitosis until their centrosomes are re-oriented (Cheng et al.), pointing to the presence of a checkpoint
mechanism that monitors correct interphase centrosome orientation prior to mitosis (the centrosome orientation checkpoint)(Inaba 2010, Yuan 2011). In this
study, we demonstrate a novel function of a polarity protein Bazooka/Par-3 in the centrosome orientation and its checkpoint. Bazooka is localized at the hub-
GSC interface forming a small “patch“, which closely associates (“engages”) with the apical centrosome in the late G2 cells right before mitotic entry.
Overexpression of Baz, which leads to even cortical localization of Baz, results in ectopic engagement of centrosome and defect in the centrosome
orientation checkpoint. Serine151 residue of Bazooka becomes highly phosphorylated in a Par-1 dependent manner, correlating with the association with the
centrosome during late G2 phase. We further provide the evidence supporting that the correct orientation of the centrosome is monitored as the engagement
between the Bazooka patch and the apical centrosome.
843C
Zfrp8/PDCD2 a new stem cell gene.
Ruth Steward, Neha Changela, Svetlana Minakhina. Waksman Inst, Rutgers Univ, Piscataway, NJ.
The lymph gland is the hematopoietic organ of Drosophila. Drosophila hematopoiesis shows many similarities to human hematopoiesis and virtually all
genes and pathways functioning in Drosophila blood formation also have an essential role in vertebrate hematopoiesis. We have shown that the embryonic
and first instar larval lymph gland contains a few cells that have similar characteristics as vertebrate hematopoietic stem cells (HSCs). We have further found
that the highly conserved Zfrp8/PDCD2 gene has an essential function in HSCs, but that it is dispensable in more mature cells. This work led us to study the
function of Zfrp8 in other stem cells and we find that it is also required in both germline and somatic stem cells in the Drosophila ovary. Consistent with our
findings, the vertebrate homolog PDCD2 has been shown to be essential for the viability of mouse embryonic stem cells. We propose that PDCD2/Zfrp8 has
a conserved role in stem cells of different species.