Poster 3
Presenter: Kari Buck
Wednesday, 3:00 – 5:00pm
K.J. Buck, L.C. Milner, R.L. Shirley, L.B. Kozell, N.A.R. Walter, N.H. Komiyama, S.G.N. Grant Portland Veterans Affairs Medical Center and Oregon Health & Science University, Wellcome Trust Sanger Institute, Cambridge, UK
Previously, we identified a QTL accounting for ~26% of the genetic variance in ethanol withdrawal (EW) convulsions in mice. Positional cloning narrowed this to a 1.8 Mb interval syntenic with human 9p24-p22.3; resident gene analyses identified allelic variation in Mpdz, resulting in different multiple PDZ domain protein (MPDZ/Mupp1) expression as potentially causal (Nat Neurosci 7:699,2004), but rigorous testing of this hypothesis has been lacking due to the dearth of targeted genetic models. Toward this end, we created Mpdz transgenic (MPDZ-TG, DBA/2 background) and knockout heterozygote (Mpdz+/-, C57BL/6 background) models. QPCR confirmed that target expression is reduced by 47% in Mpdz+/- brain, and increased 2.9-fold in MPDZ-TG, compared to wildtype littermates (WT). Neither baseline (pre-ethanol) nor PTZ enhanced handling-induced convulsion (HIC) scores differ between WT and their respective model, demonstrating that Mpdz does not affect seizure susceptibility in general. As predicted, EW scores were lower in MPDZ-TG than WT (6.2±0.7 and 9.6±1.2), and higher in Mpdz+/- than WT (3.9±0.7 and 1.9±0.6) (p<0.03). Thus, varying Mpdz gene dosage regulates EW, with an inverse relationship between Mpdz expression and EW severity. The strengths of the transgenic approach complement the limitations of the knockout approach, and vice versa, so both supporting MPDZ’s role in EW is compelling. Mpdz+/- consume less 6%, 10% and 20% ethanol (p<0.05) than WT, but do not differ in water consumption across ethanol self-administration (ES) days. These are the first data to implicate Mpdz in ES and the genetic relationship between EW and ES.