Page 314 - 53rd Annual Drosophila Research Conference

Poster Full Abstracts - Neural Development
Poster board number is above title. The first author is the presenter
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677B
Dissecting the cis-regulatory enhancers that control the POU-domain transcription factor genes, pdm-1 & pdm-2. Jermaine Ross, Thomas Brody,
Mukta Kundu, Alexander Kuzin, Ward F Odenwald. NINDS, NIH, Bethesda, MD.
While neuroblast (NB) lineage studies have identified transcription factor (TF) genes important to cell identity decisions, we currently have only an
incomplete understanding of the cis-regulatory elements that control their expression. To identify, compare, and functionally test these regulatory sequences,
we have employed transgenic reporter assays along with our comparative genomic programs, EvoPrinter and cis-Decoder (also see Kundu et. al and Brody
et al. abstracts). Here, we describe the enhancers that regulate the pdm-1 & pdm-2 genes. These POU-domain TF paralogs carry out overlapping functions
during CNS lineage development. Thus far, we have identified over 20 enhancers that are located within a 125 kb region that spans the pdm-1 & -2 locus on
the second chromosome. Our studies have shown that these enhancers are functionally autonomous and control different subsets of the pdm expression
patterns during embryonic, larval and/or adult CNS development. Among these, we have identified pdm-1 & -2 enhancers that activate expression in
overlapping subsets of NBs. For example, enhancers that drive transgene activity in overlapping but nonidentical expression patterns during intermediate
stages of NB lineage development. Further, cis-Decoder analysis of the conserved DNA within the NB enhancers identifies shared and unique conserved
sequences. Site-directed mutagenesis of these conserved sequences reveal that they are important for cis-regulation. One of the tested sequences includes a
highly conserved 9-mer sequence, TAAAAATTG, identified in both the pdm-1 & -2 NB enhancers. Based on previous work, this sequence corresponds to
the DNA binding site of Castor, a zinc-finger TF that is required for proper pdm expression. We found that absence of the 9-mer sequence triggers ectopic
reporter expression in the cephalic lobes. Currently, we are testing the functional significance of other putative pdm enhancers identified through EvoPrinter
and cis-Decoder analysis, and will report these findings.
678C
Molecular basis of the production of neuronal diversity in the Drosphipha visual center. Takumi Suzuki, Masako Kaido, Rie Takayama, Makoto Sato.
Frontier Science Organization, Kanazawa University, Kanazawa, Japan.
The medulla, the primary region of the optic lobe, shares structural features with a mammalian brain such as layer and columnar structures and contains 60
types of 40,000 neurons. So far, the developmental mechanisms that produce such neuronal diversity are largely unknown. Our recent study revealed that the
medulla is subdivided into concentric zones that are characterized by the expression of four conserved transcription factors (Homothorax (Hth), Brain-
specific homeobox (Bsh), Runt (Run), Drifter (Drf); collectively called concentric genes) during larval development (Hasegawa et al., Development 138,
983- (2011)). Although these concentric genes contribute to defining each neuronal type, regulatory mechanisms underlying specification of their expression
are unclear at all despite their functional importance. In the embryonic central nervous system, the neuronal type is defined by transcription factors that are
sequentially expressed in the neuroblasts (NBs: Isshiki et al., Cell 106, 511- (2001)). In the medulla, NBs situated on the cortical surface generate neurons
and birth order of the neurons correlates with the concentric gene expression. This suggests that types of the medulla neurons are specified in a birth order-
dependent manner. We therefore searched for genes that are temporally expressed in the medulla NBs and found a group of candidate genes. Among them,
sloppy-paired (slp) is expressed in the newly produced NBs while Dicheate (D) is expressed in the older ones. To investigate roles of these genes, we
generated gain-of-function and loss-of-function clones for each gene. In clones expressing slp, ectopic Bsh expression was observed. In slp mutant clones,
Run and Drf expression was induced ectopically. In clones expressing D, ectopic Run expression was observed. By contrast, knock-down of D resulted in
disruption of Run domain. These results suggest that sequential expression of slp and D in NBs is involved in specification of concentric gene expression,
and that types of medulla neurons are specified in a birth order-dependent manner.
679A
Drosophila motor neuron retraction mediated by inputs from TGF-β/BMP signaling and orphan nuclear receptors. Jean-Maurice Dura 1, Ana
Boulanger1 , Morgane Farge1, Christophe Ramanoudjame 1, Kristi Wharton1,2 . 1) Inst of Human Genetics, CNRS/UPR 1142, Montpellier , France; 2) Dept of
Molecular Biology, Brown University, Providence, RI, USA.
Larval motor neurons remodel during Drosophila neuro-muscular junction (NMJ) dismantling at metamorphosis. In this study, we describe the motor
neuron retraction as opposed to degeneration based on the early disappearance of β-Spectrin and the continuing presence of Tubulin. Importantly, we show
the presence of peripheral glial cells close to the neuro-muscular junction that retracts before the motor neuron. By blocking cell dynamics with a dominant-
negative form of the Dynamin, we show that glial cell and macrophages have key role in this process. We show also that expression of EcR-B1, encoding the
steroid hormone receptor required for muscle dismantling, is under the control of the ftz-f1/Hr39 orphan nuclear receptor pathway. In the motor neuron,
activation of EcR-B1 expression by the two parallel pathways (TGF-β signaling and nuclear receptor) triggers axon retraction. We propose a model for the
sequential events that are occurring during NMJ dismantling at early metamorphosis. First, EcR-B1 is expressed in the muscle under the control of FTZ-F1.
FTZ-F1 activates EcR-B1 and represses Hr39. This repression is compulsory for EcR-B1 activation. Importantly, TGF-β/BMP signaling does not appear to
be required for EcR-B1 activation in this tissue, however, a result of EcR-B1 activation in the muscle would be the production of a secreted TGF-β family
ligand. Then, this secreted TGF-β family ligand reaches the appropriate receptors and activates the TGF-β signaling in the motor neuron. Finally, TGF-β
signaling in association with the nuclear receptor pathway activates EcR-B1 expression resulting in motor neuron retraction. The requirement of the two
pathways in the motor neuron provides a simple molecular explanation of the instructive role of postsynapse degradation on motor neuron retraction. This
mechanism insures the temporality of the two processes and prevents motor neuron pruning before postsynaptic degradation.
680B
Axonal transport and synaptic function are linked in two Drosophila disease models of neurodegeneration. Shermali Gunawardena1 , Min Jung Kang1,
Monique Michiewicz2, Hong Bao1, Samantha Fye1, Tadeusz J. Kaczynski2, Bing Zhang1 , Shermali Gunawardena1 . 1) Biological Sciences, SUNY at Buffalo,
Buffalo, NY; 2) Department of Zoology, University of Oklahoma, Norman, Oklahoma 73019.
Formation of new synapses or maintenance of existing synapses requires the delivery of synaptic components from the soma to axodendritic sites via
axonal transport. However, the link between transport and synaptic function is poorly understood. Previously we found that expression of disease proteins;
pathogenic polyQ repeat protein or human amyloid precursor protein with an FAD mutation (SWE) caused axonal transport defects. Here we show that