Hung-Lin Chen and Melissa Marchal will Present their Research Thursday, 7/23/15
DEFICIENCY SCREENING; IDENTIFICATION OF GLUTATHIONE S-TRANSFERASE 1 AS A GENETIC MODIFIER OF THE DROSOPHILA VOLTAGE-GATED SODIUM CHANNEL GENE, PARALYTIC
Hung-Lin Chen, Toshihiro Kitamoto
Voltage-gated sodium (Nav) channels are essential for generation and propagation of action potentials in neurons. Dysfunction of Nav channels often causes neuronal hypo- or hyper-excitability, resulting in a variety of neurological disorders, such as epilepsy. Epilepsy is one of the most common neurological disorders in the world. As estimated 50 million people worldwide suffer from this devastating pathological condition and a significant portion of patients (~30%) do not respond to anti-epileptic drugs (AEDs). Thus, identifying new target genes for AEDs is of emergent clinical need. In this study, I take advantage of Drosophila genetics to identify modifier genes that can reduce neurological phenotypes caused by mutations in the Nav channel gene, paralytic (para). Shudderer (Shu) is a mutant allele of para, displaying neuronal hyper excitability as well as behavioral and morphological abnormalities. These include seizure-like behaviors, down-turned wings, and indented thorax. Here we carried out a deficiency screen to identify modifiers of Shu. Our working hypothesis is that the Shu mutant phenotypes are enhanced or suppressed when the activity of genes functionally interacting with Shu is reduced by 50%. We systematically introduced molecularly defined deficiencies into the Shu mutant background and tested if it results in a modification of the mutant neurological phenotypes. After morphological and behavioral analyses, we identified a short genomic deletion in the second chromosome that can ameliorate Shu’s phenotypes. This deletion covers six genes. By using RNA interference and P-insertion mutants, we narrow down the modifier of Shu to glutathione s-transferase 1 (GstS1). GstS1 mutations reduced frequency of seizures in another Drosophila Nav channel mutant that carries a mutation causing genetic epilepsy with febrile seizures plus (GEFS) in humans. Immunochemistry showed a GstS1 mutation increases GABA levels in the Shu mutant brain. It indicates that deletion of GstS1 may reduce neurological phenotype of Shu by enhancing GABAergic inhibition. Since Drosophila and human share fundamental biological pathways, my study may provide a new direction for AED development.
THE ROLE OF MATERNAL WNTS AND FRIZZLEDS IN DORSO-VENTRAL AXIS SPECIFICATION
Melissa Marchal1 and Douglas Houston1
1The Interdisciplinary Program in Genetics and The Department of Biology, University of Iowa, Iowa City, IA, 52242
The proper localization of maternal mRNAs and proteins in the egg is required for many developmental processes, including dorsoventral (DV) axis determination. In Xenopus laevis in particular, maternal factors involved in patterning the DV body axis are localized during oogenesis to the oocyte vegetal cortex. Upon sperm entry, these determinants are translocated to the future dorsal side of the embryo, in a microtubule dependent process called cortical rotation. The major outcome of cortical rotation is the asymmetric activation of the Wnt/β-Catenin signaling pathway in dorsal nuclei, where β-Catenin acts to transcriptionally activate dorsal-specific genes at the midblastula transition. However, the upstream mechanisms initiating β-catenin stabilization have remained elusive. Recent evidence has suggested that secreted Wnt ligands Wnt11 and Wnt5a may act together in axis formation. However, the function of other maternally expressed Wnts and their cognate receptors (frizzleds) remains uncharacterized. We have examined the expression of wnts and frizzleds (fzds) in the oocyte and throughout early development. Through this analysis, we have found that fzds 1, 4, 6, and 7 are expressed abundantly in the oocyte, with fzd7 maintaining high expression levels until the tailbud stages. Using a maternal depletion approach we have begun to identify the roles of these maternal factors in DV axis patterning. We present evidence that maternal fzd1-depleted embryos show a ventralization phenotype and partial defects in dorsal-specific gene expression, while fzd4-depleted embryos show a dorsalization phenotype and the expansion of dorsal-specific markers. Additionally, we show that oocytes depleted of fzds 1, 4, and 7, have significant microtubule defects, suggesting that Frizzled-dependent signaling may play a role in cortical rotation.