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Poster Full Abstracts - Neural Development
Poster board number is above title. The first author is the presenter
307
656B
Characterization of the neural expression and roles of the Ret tyrosine kinase receptor.
Daniel Perea, Irene Miguel-Aliaga. Zoology, Cambridge
University, Cambridge, Cambridge, United Kingdom.
In mammals, the RET tyrosine kinase receptor plays an important role in the regulation of kidney development and the specification of peripheral neurons,
including sympathetic, parasympathetic and enteric neurons. In the nervous system, absence of RET has been shown to have a crucial role in the migration
of sympathetic precursors and the specification of parasympathetic neurons. RET mutation also leads to defects in the survival, migration and proliferation
of enteric neurons: a condition known as Hirschsprung's disease in humans. The Drosophila homologue of RET (dRet or Ret) has been cloned, and has been
shown to be expressed in multiple tissues during embryogenesis, including the yolk sac, the stomatogastric nervous system and the developing Malpighian
tubules (Hahn and Bishop, PNAS, 2000). Ret mRNA is also apparent in the central and peripheral nervous system (Sugaya et al, Mechanism of
Development, 1993). This conserved neuronal expression in flies has prompted us to investigate whether, like its mammalian counterpart, Ret controls the
specification of Drosophila intestinal neurons. As a first step towards investigating its functions, we have characterized Ret expression in embryonic, larval
and adult enteric neurons. Our expression analysis indicated that Ret is expressed in different subsets of hindgut-innervating neurons throughout
development. Experiments are currently underway to establish its significance in the specification and function of these neuronal subpopulations.
657C
Disassembling F-actin Networks Through Manipulations of Mical and Actin Bundling Proteins.
Jimok Yoon, Heng Wu, Jonathan Terman. Center for
Basic Neuroscience, U.T.Southwestern Medical Center at Dallas, Dallas, TX.
Cells continually interact with their environment and change their morphology in response to extracellular cues. Semaphorins are one of the largest
families of these extracellular guidance cues and play critical roles in neurobiology, immunology, cardiovascular health, and cancer. Semaphorins are best
known for their ability to disassemble actin filaments (F-actin) and we recently found that Mical, a protein that directly associates with the Semaphorin cell-
surface receptor Plexin, is a novel F-actin disassembly factor that mediates Semaphorin/Plexin F-actin rearrangements. Herein, we use genetic approaches in
the Drosophila model system and in vitro actin biochemical approaches with purified proteins to further investigate Mical-mediated F-actin alterations. We
find that Mical and F-actin stabilizing/bundling proteins such as fascin and espin play antagonistic roles in regulating the F-actin cytoskeleton during
development in vivo. Consistent with our in vivo data, we find that purified Mical protein disassembles fascin and espin bundled actin filaments in vitro. Our
results go on to support a hypothesis that Semaphorin/Plexin/Mical directly disassembles the F-actin cytoskeleton and by so doing, triggers other actin
regulatory proteins to reorganize a more complex F-actin network.
658A
The fate of identified dHb9-positive larval motor neurons during metamorphosis.
Soumya Banerjee, Marcus Toral, Matthew Siefert, Joyce Fernandes.
Zoology, Miami Univ, Oxford, OH.
During metamorphosis the nervous system is remodeled- a process which involves generation, re-specification, and elimination of specific neurons to form
new adult-specific neural circuits. Many of the larval muscle fibers and motor neurons are eliminated during this time period to allow for the development of
an adult motor system. Interestingly, some larval muscle fibers persist into the adult and function in eclosion. The focus of this study is to observe the fate of
dHb9 expressing larval motor neurons which innervate a pair of ventral larval muscles (MF12 and MF13) which persist to the adult stage. These muscles
selectively persist in the A1 and A2 segments. Since these muscle fibers are required for eclosion and then die, we propose that the cognate motor neurons
will persist and then be eliminated after eclosion. To visualize individual motor neurons, we employ the ‘flip-out’ approach in conjunction with live imaging.
Our preliminary studies have determined that in A1 and A2, larval MN12-1b maintains its larval pre-synaptic target, MF12, through metamorphosis and into
the adult stage (n=14). However, we find that larval MN13-Ib changes its target from MF13 to adult specific ventral muscles in A1 and A2 during
metamorphosis (n=4). Additionally, we have observed that the persistent MF13 is innervated in the adult stage by one of three dHb9-positive neurons;
neurons belonging to a dorsal cluster of identified neurons in the ventral ganglion (n=14). Finally, we have also shown through TUNEL assays that the motor
neuron innervating adult muscle fiber 13 shows signs of cell death around 4-6 hours post eclosion (n=10), much earlier than the time-point when the muscle
fiber itself is eliminated. Our current work is aimed at identifying which member of the dorsally located neural cluster innervates persistent larval MF 13 in
the adult. These studies will contribute to our lab’s goal in following the re-specification of identified larval motor neurons to their adult fates.
659B
Neurotrophic actions of dopamine on the development of a serotonergic feeding circuit in
Drosophila melanogaster
.
Parag Bhatt, Wendi Neckameyer.
Pharmcological and Physiological Science, Saint Louis University School of Medicine, St Louis, MO.
In the fruit fly,
Drosophila melanogaster
, serotonin functions both as a neurotransmitter to regulate larval feeding, and in the development of the
stomatogastric feeding circuit. There is an inverse relationship between neuronal serotonin levels during late embryogenesis and the complexity of the
serotonergic axonal fibers projecting from the larval brain to the foregut, which correlate with perturbations in feeding, the functional output of the circuit.
Dopamine does not modulate larval feeding, and dopaminergic fibers do not innervate the larval foregut. However, both decreased and increased neuronal
dopamine levels during late embryogenesis result in depressed levels of larval feeding and hypersensitive feeding responses to the neurotransmitter actions
of serotonin. Perturbations in neuronal dopamine during development also result in greater branch complexity of the serotonergic axonal fibers innervating
the gut, as well as increased size and number of the serotonergic presynaptic vesicles along the neurite length. This neurotrophic action for dopamine is
modulated by the dopamine D2 receptor expressed during late embryogenesis in central 5-HT neurons. Animals carrying transgenic RNAi constructs to
knock down both dopamine and serotonin synthesis in the central nervous system display normal feeding and fiber architecture. However, disparate levels of
neuronal dopamine and serotonin during development result in abnormal gut fiber architecture and feeding behavior. These results suggest that DA can exert
a direct trophic influence on the development of a specific neural circuit, and that the actions of both dopamine and serotonin are critical for its development.
National Science Foundation Grant No. 0616062 and The President’s Fund, Saint Louis University.
660C
RNA-seq reveals diverse neurosecretory properties of the CNS-midline cells in
Drosophila
.
Joseph R. Fontana
1
, Stephen T. Crews
1,2
. 1) Molecular