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Poster Full Abstracts - Gametogenesis and Organogenesis
Poster board number is above title. The first author is the presenter
280
554B
Investigating a mesenchymal to epithelial tranisition during development of the testis niche.
Lindsey Wingert
1,2
, Stephen DiNardo
2
. 1) Cell and
Molecular Biology, University of Pennsylvania, Philadelphia, PA; 2) Cell and Developmental Biology, University of Pennsylvania, School of Medicine,
Philadelphia, PA.
The testis is an excellent system for studying stem cell-niche interactions. The hub (niche) cells residing at the apical tip of the testis provide germline stem
cells (GSCs) and cyst stem cells (CySCs) with signals promoting attachment and self-renewal, thus allowing them to maintain production of sperm for the
lifetime of the animal. Much has been discovered about the key signaling pathways involved in steady state maintenance. However, less is known about how
the architecture of the adult germline stem cell niche is achieved. During gonadogenesis, somatic gonadal precursors (SGPs) exhibit partial mesenchymal
identity as they migrate and coalesce with germ cells (Jenkins et al., 2003, Development 130:4417-4428). Hub cells are specified from the pool of SGPs by
Notch activation (Kitadate and Kobayashi, 2010, Proc Natl Acad Sci USA. 107(32):14241-6 and Okegbe and DiNardo, 2011, Development 138(7):1259-
67). By the end of embryogenesis, hub cells form a true epithelium at the anterior pole of the gonad by remodeling cell-to-cell and cell-to-matrix adhesions
(Tanentzapf et al., 2007, Nat Cell Biol 9:1413-1418, and Le Bras and Van Doren, 2006, Dev. Biol. 294:92-103). There are several markers expressed
broadly in SGPs that become restricted to or repressed in hub cells during this transition. Both the morphological and genetic states adopted by hub cells
during embryogenesis are maintained throughout the steady-state function of the testis. We are investigating the roles of the transcription factors Traffic jam
(Tj) and Zfh-1 in the mesenchymal to epithelial transition (MET) using genetics and live imaging of hub formation. We suspect that the downregulation of
these proteins is critical for refining gene expression associated with terminal differentiation in niche cells.
555C
Hoi polloi is a specific regulator of somatic muscle differentiation.
Aaron N. Johnson, Eric N. Olson. Department of Molecular Biology, University of
Texas Southwestern Medical Center at Dallas, Dallas, TX.
A key interest in the field of muscle biology is to understand the molecular processes by which a specified muscle precursor undergoes the complex
cellular and morphological changes to become a contractile, mature muscle. Using a forward genetic approach, we identified an essential function for the
RNA binding protein Hoi Polloi (Hoip) during terminal muscle differentiation. Hoip belongs to an ancient family of RNA binding proteins that includes
Snu13p in yeast and NHP2L1 in humans, both of which are key components of the spliceosome.
hoip
mutant embryos have a striking phenotype in which
somatic muscle founder cells are correctly specified but the sarcomere component Myosin Heavy Chain (MHC) is not expressed. Surprisingly, in
hoip
embryos, F-actin assembles at wild type levels in the somatic musculature and MHC is expressed normally in the visceral musculature. Hoip therefore
regulates the processing of a specific set of RNAs within the somatic mesoderm. Accordingly, we found that
hoip
is expressed solely in the mesoderm and
the endoderm but, within the mesoderm,
hoip
expression is excluded from the visceral muscle lineage. We have identified a minimal enhancer that
recapitulates
hoip
embryonic expression and found a highly conserved E-box sequence that is necessary for enhancer activity. To elucidate the mechanism
by which Hoip regulates muscle differentiation, we have generated a series of distinct point mutations in the Hoip cDNA that are being used for functional in
vivo rescue experiments. Expressing wild type Hoip in muscle founder cells rescues the
hoip
muscle phenotype, and we expect that mutant Hoip transgenic
rescue experiments will clarify the function of Hoip during myogenesis. In addition, we are deep sequencing RNA from
hoip
embryos to evaluate the role of
Hoip in regulating RNA expression and processing. This study has identified a novel, muscle-specific RNA regulatory network that directs terminal somatic
muscle differentiation and will provide unique insights into the molecular events that direct muscle morphogenesis.
556A
JAK/Stat signaling regulates heart precursor diversification in
Drosophila
.
Aaron N. Johnson, Mayssa H. Mokalled, Thomas N. Haden, Eric N. Olson.
Department of Molecular Biology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX.
Intercellular signal transduction pathways regulate the NK-2 family of transcription factors in a conserved gene regulatory network that directs
cardiogenesis in both flies and mammals. The Drosophila NK-2 protein Tinman (Tin) was recently shown to regulate Stat92E, the Janus Kinase (JAK) and
Signal Transducer and Activator of Transcription (Stat) pathway effector, in the developing mesoderm. To understand if the JAK/Stat pathway also regulates
cardiogenesis, we performed a systematic characterization of JAK/Stat signaling during mesoderm development. Drosophila embryos with mutations in the
JAK/Stat ligand
upd
or in
Stat92E
have non-functional hearts with luminal defects and inappropriate cell aggregations. Using strong
Stat92E
loss-of-
function alleles, we show that the JAK/Stat pathway regulates
tin
expression prior to heart precursor cell diversification.
tin
expression can be subdivided
into four phases, and, in
Stat92E
mutant embryos, the broad Phase-2 expression pattern in the dorsal mesoderm does not restrict to the constrained Phase-3
pattern. These embryos also have an expanded pericardial cell domain. We show the E(spl)-C gene
HLHm5
is expressed in a pattern complementary to
tin
during Phase-3 and that this expression is JAK/Stat dependent. In addition, E(spl)-C mutant embryos phenocopy the cardiac defects of Stat92E embryos.
Mechanistically, JAK/Stat signals activate E(spl)-C genes to restrict Tin expression and the subsequent expression of the T-box transcription factor H15 to
direct heart precursor diversification. This study is the first to characterize a role for the JAK/Stat pathway during cardiogenesis and identifies an
autoregulatory circuit in which
tin
limits its expression domain.
557B
A role for
Drosophila
Cyclin J in oogenesis is uncovered in piRNA pathway mutants.
Paul Michael Albosta, Govindaraja Atikukke, Huamei Zhang,
Russell Finley. Ctr Molecular Medicine & Genetics, Wayne State Univ Sch Medicine, Detroit, MI.
Cyclin J (
CycJ
) is a poorly characterized member of the cyclin superfamily of proteins, many of which regulate the cell division cycle.
CycJ
mRNA in
Drosophila
is limited to ovaries and early embryos, suggesting a role in one or both of these tissues.
CycJ
is adjacent to
armitage (armi)
, a gene involved in
the piwi-associated RNA (piRNA) pathway. Mutants of
armi
and other piRNA pathway members are known to result in germline defects including
transposon upregulation, DNA damage accumulation, and oocyte axis specification defects, but the function of
CycJ
during oogenesis has yet to be
determined. We examined the roles for both
armi
and
CycJ
during oogenesis using null mutant flies created by deleting
CycJ
and
armi
and then
complementing with transgenes for each gene individually. We demonstrate the previously defined role of
armi
in axis specification and further find that
complete loss of
armi
leads to an apparent germline stem cell loss similar to
piwi
mutants. These
armi
null flies produce ovarioles with only two to three egg
chambers, most of which contain the normal complement of 15 nurse cell nuclei and one oocyte. While
CycJ
null mutants display no obvious oogenesis