title: Elevated expression of the G-protein-activated inwardly rectifying potassium channel 2 (GIRK2) in cerebellar unipolar brush cells of a Down syndrome mouse model.
abstract: 1. Down syndrome (DS) arises from the presence of three copies of chromosome (Chr.) 21. Fine motor learning deficits found in DS from childhood to adulthood result from expression of extra genes on Chr. 21, however, it remains unclear which if any of these genes are the specific causes of the cognitive and motor dysfunction. DS cerebellum displays morphological abnormalities that likely contribute to the DS motor phenotype. 2. The G-protein-activated inwardly rectifying potassium channel subunit 2 (GIRK2) is expressed in cerebellum and can shunt dendritic conductance and attenuate postsynaptic potentials. We have used an interbreeding approach to cross a genetic mouse model of DS (Ts65Dn) with Girk2 knockout mice and examined its relative expression level by quantitative real-time RT-PCR, Western blotting and immunohistochemistry. 3. We report here for the first time that GIRK2 is expressed in unipolar brush cells, which are excitatory interneurons of the vestibulocerebellum and dorsal cochlear nucleus. Analysis of disomic-Ts65Dn/Girk2((+/+/-)) and heterozygous-Diploid/Girk2((+/-)) mice shows that GIRK2 expression in Ts65Dn lobule X follows gene dosage. The lobule X of Ts65Dn mice contain greater numbers of unipolar brush cells co-expressing GIRK2 and calretinin than the control mouse groups. 4. These results demonstrate that gene triplication can impact specific cell types in the cerebellum. We hypothesize that GIRK2 overexpression will adversely affect cerebellar circuitry in Ts65Dn vestibulocerebellum and dorsal cochlear nucleus due to GIRK2 shunting properties and its effects on resting membrane potential.
authors.affiliation: Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, School of Medicine, Bethesda, Maryland 20814, USA.
authors.forename: Chie
authors.initials: C
authors.lastname: Harashima
authors.forename: David M
authors.initials: DM
authors.lastname: Jacobowitz
authors.forename: Markus
authors.initials: M
authors.lastname: Stoffel
authors.forename: Lina
authors.initials: L
authors.lastname: Chakrabarti
authors.forename: Tarik F
authors.initials: TF
authors.lastname: Haydar
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Siarey
authors.forename: Zygmunt
authors.initials: Z
authors.lastname: Galdzicki
mesh_terms: D000818:Animals; D064032:Calbindin 2; D016764:Cell Polarity; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D004195:Disease Models, Animal; D004314:Down Syndrome / Q000378:metabolism*; D005260:Female; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000235:genetics / Q000378:metabolism*; D018628:Gene Dosage; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008871:Microvilli / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism
chemical_list: C576511:Calb2 protein, mouse; D064032:Calbindin 2; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C497069:Kcnj6 protein, mouse; D064030:S100 Calcium Binding Protein G