Abstracts - Society for Developmental Biology

91
Program/Abstract # 278
Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is crucial for the regeneration of Xenopus optic axons
Szaro, Ben G.; Liu, Yuanyuan; Yu, Hurong, State University of NY at Albany, United States
Neurons express unique structural proteins that organize the cytoskeleton into an axon. During axon outgrowth, expression
of these proteins is tightly coordinated to meet ever-shifting demands for structural materials. For example, in Xenopus
optic nerve regeneration, changes in neurofilament protein expression result from a complex interplay between
transcriptional and post-transcriptional gene regulatory mechanisms. In developing Xenopus neurons, the RNA-binding
protein, hnRNP K, plays an essential role in the trafficking and translation of not only neurofilament mRNAs, but also the
mRNAs of additional cytoskeletal proteins involved in organizing the axonal cytoskeleton, and which collectively are
required for axonogenesis. To test whether hnRNP K plays a similar role in the post-transcriptional control of these genes
during Xenopus optic axon regeneration, we used intravitreal injection of antisense Vivo-Morpholino oligonucleotide to
suppress hnRNP K expression. In uninjured eye, knockdown was restricted to the retinal ganglion cell (RGC) layer and
induced neither an axotomy response nor axon degeneration. After crush injury, hnRNP K knockdown prevented regrowth
of axons beyond the lesion site. The injured RGCs nonetheless responded by increasing expression of several growthassociated
RNAs, but those that were regulated by hnRNP K exhibited defects in nuclear export and failed to be loaded
onto polysomes for translation. Thus, hnRNP K is an essential component of a novel post-transcriptional regulatory
pathway that is essential for successful CNS axon regeneration. Funded by NSF IOS 951043 and an AHA Predoctoral
Fellowship to YL.
Program/Abstract # 279
Buffy rescues and debcl enhances a-synuclein induced phenotypes in Drosophila
M'Angale, Peter; Staveley, Brian, Memorial University, St. John's, Canada
To more fully understand the biological basis of Parkinson disease (PD), we study aspects of the disease in the very well
understood model organism, Drosophila melanogaster.In brief, the directed expression of α-synuclein,the first gene
identified to contribute to inherited forms of PD, to the dopaminergic neurons of flies has provided a robust and wellstudied
Drosophila model of PD complete with the loss of neurons and accompanying motor defects. In contrast to the
complexity found in mammals, only two Bcl-2 family member genes have been found in Drosophila: the pro-cell survival
Buffy and, debcl, the sole anti-cell survival homologue. In the α-synuclein-induced Drosophila model of PD, we have
altered the expression of Buffy and debcl in the dopamine producing neurons and, in complementary experiments, in the
developing neuron-rich eye. When these two genes were overexpressed in the dopamine producing neurons, debcl
enhanced the α-synuclein-induced loss of climbing ability over time while Buffy acted t orescue this phenotype. In an
analogous manner, when over expressed in the developing eye, Buffy suppressed and debcl enhanced the severity of the α-
synuclein-induced disruption of the ommatidial array. Taken together, these experiments suggest a potentially protective
role for Buffy and a potentially detrimental one for debclin α-synuclein-induced protein toxicity and possibly in Parkinson
disease.
Program/Abstract # 280
The role of calcium signaling and voltage-gated calcium channels in neurotransmitter phenotype specification
Schleifer, Lindsay; Lewis, Brittany; Saha, Margaret, College of William and Mary, Williamsburg, United States
There has been a significant amount of research analyzing the ‘hard-wired’ aspects of nervous system development, such
as the role of transcriptional regulation.However, recent literature points to another, relatively novel, mechanism forneuro
transmitter phenotype specification: spontaneous electrical activity in the form of calcium transients. Calcium plays a
critical role in neuronal development and its activity seems to play an essential role in neuronal phenotype specification,
particularly neurotransmitter phenotype. Calcium ionfluctuations occur at early stages of neuronal development and
alterations in this activity in Xenopus laevis have been shown to modify the ratio of excitatory and inhibitory neurons. Our
overarching hypothesis is that voltage-gated calcium channels mediate the spontaneous activity found in embryonic
neurons. By imaging changes in intracellular calcium concentrations using confocal microscopy, we have correlated
expression of voltage-gatedcalcium channels (VGCCs) with specific patterns of activity on a single-celllevel. Eight VGCC
a1 subunits are expressed in neural tissues during development, and of them, CaV2.1and CaV2.2 are associated with high
frequency activity. Pharmacological blockade of VGCCs disrupts neurotransmitter phenotype specification in cell cultures
dissected from Xenopus neural ectoderm, leading to an increase in the number of cells synthesizing glutamate and a
decrease in the number of cells synthesizing GABA. These studies provide strong evidence that calcium entry through
VGCCs plays an important role in neuronal phenotype specification.