Consequences of Altered Expression of Gaba Receptors During Neural Embryonic Development in Response to Low Levels of Mercury

Fifth International Symposium on Recent Advances in Environmental Health Research POSTER SESSION B

PB - 19

CONSEQUENCES OF ALTERED EXPRESSION OF GABA RECEPTORS DURING NEURAL EMBRYONIC DEVELOPMENT IN RESPONSE TO LOW LEVELS OF MERCURY

Wellington K. Ayensu1, Raphael D. Isokpehi1, Jessica M. Murray1, Hari H.P. Cohly1 and Paul B. Tchounwou1

1 2 Department of Biology, Jackson State University, Jackson MS 39217 Cellomics and Toxicogenomics Research Laboratory, NIH-RCMI Center for Environmental Health, College of Science, Engineering and Technology, Jackson State University, Jackson, MS 39217, USA

Abstract: We have previously observed that Gamma-AminoButyric Acid (GABA) A receptor, alpha 6 (GABRA6) in HepG2 cells were up-regulated upon exposure to low doses of mercury (2μg/mL) compared to control samples. There over 20 known GABA receptor subunits that form varieties of functional clusters throughout parts of the brain to generate neurotransmitters for specific activities. Exposure to mercury in the prenatal period can lead to the induction of high expression levels of these receptors sufficient to guide pathological neuronal networking through effects on genes expressed. Therefore, the up-regulation of GABRA6 led us to investigate the pattern of expression of the GABA receptor family in the brain during the course of mammalian embryogenesis. The functional capabilities of individual receptor subunits influence the quality of signaling in different parts of the brain through formation of specific pentamers that display characteristic influence with neurotransmitters release. We have taken advantage of published gene expression datasets to investigate the temporal expression of mammalian GABA receptors. We identified a Gene Expression Omnibus (GEO) dataset (GDS2702) derived from microarray experiments with developing mammalian brain on embryonic days 14.5 (E14.5), 16.5 (E16.5 and 18.5 (E18.5). This microarray dataset included expression information on RNA samples derived from brains of wild-type mice which is the microarray sample set we desired. Therefore, we analyzed sample series GSM124777 (E14.5), GSM124779 (E16.5) and GSM124781 (E18.5) for expression of GABA receptors genes that are present on the oligo microarray chip platform (GEO GPL 81; Affymetrix GeneChip Murine Genome U74 Version 2 Set MG- U74A). To provide a more comprehensive understanding of the expression of GABA receptors during developmental stages, we integrated microarray intensity calls (presence or absence of expression) data with expression image data annotation from in-situ hybridization transcriptome of mouse embryo at E14.5. A total of 14 probes on the array slide mapped to 13 GABA receptor genes. Gabbr1, Gabra2, Gabrb3 and Gabrg2 were the only four GABA receptor genes expressed at stage E14.5 and E16.5. However, at stage E18.5, three additional genes (Gabra1, Gabra3, Gabrg1 and Gabrg3) were expressed. Gabbr1 had the highest intensity in all the three embryonic days. Gabra6, Gabrb2, Gabrd, Gabrr1 and Gabrr2 were not expressed in all the 3 samples analyzed. In general, there were correlations in the annotations from microarray and in-situ hybridization assayed expression of GABA receptor genes in the developing mouse brain at stage E14.5

Acknowledgements: Mississippi NSF-EPSCoR “Innovations through Computational Sciences” Award (EPS-0556308); the Research Centers in Minority Institutions (RCMI) – Center for Environmental Health (NIH-NCRR G12RR13459-09); Interdisciplinary Undergraduate Training in Biological and Mathematical Sciences (DMS-0531927); NIH Grant No. 5P20RR16470-02/USM-GR00978-04; U.S. DoA Grant No. DACA-42-02-C-0057 (MACERAC program) and NIH-EARDA (1G11HD046519-03).