Deletion of the Mouse Glycine Transporter 2 Results in a Hyperekplexia Phenotype and Postnatal Lethality
Authors: Jesús Gomeza, Koji Ohno, Swen Hülsmann, Wencke Armsen, Volker Eulenburg, Diethelm W Richter, Bodo Laube, Heinrich Betz
Journal: Neuron (2003)

porter 1 (GlyT1).GlyT1 Ϫ/Ϫ mice die on the first postnatal Deutschordenstrasse 46 day, due to severe motor and respiratory deficits re-60528 Frankfurt sulting from overinhibition (Gomeza et al., 2003 [this issue Germany of Neuron]).Here, we describe a mouse line that lacks 2 Department of Neuro-and Sensory Physiology functional glycine transporter 2 (GlyT2), the neuronal University of Go ¨ttingen GlyT isoform localized in presynaptic terminals of gly-Humboldtallee 23 cinergic interneurons (Zafra, 1995a; Spike et al., 1997).37073 Go ¨ttingen We report that GlyT2-deficient mice display a severe Germany neuromotor disorder characterized by muscular spasticity.The animals die during the second week after birth, revealing a previously unrecognized vital role for GlyT2 Summary in postnatal life.The phenotype of these mice is consistent with GlyT2 being essential for replenishing the cyto-The glycine transporter subtype 2 (GlyT2) is localized plasmic pool of glycine that is needed for transmitter in the axon terminals of glycinergic neurons.Mice defiloading of synaptic vesicles in glycinergic nerve termicient in GlyT2 are normal at birth but during the second nals.Moreover, it mimics symptoms seen in human hepostnatal week develop a lethal neuromotor deficiency reditary hyperekplexia (or startle disease) and therefore that resembles severe forms of human hyperekplexia identifies the GlyT2 gene as a candidate disease gene (hereditary startle disease) and is characterized by spasin human patients.Together, our two studies define disticity, tremor, and an inability to right.Histological and tinct roles of GlyT1 and GlyT2 in glycine-mediated synimmunological analyses failed to reveal anatomical aptic transmission.or biochemical abnormalities, but the amplitudes of glycinergic miniature inhibitory currents (mIPSCs) were strikingly reduced in hypoglossal motoneurons and Results dissociated spinal neurons from GlyT2-deficient mice.Thus, postnatal GlyT2 function is crucial for efficient Generation of GlyT2 Ϫ/Ϫ Mice transmitter loading of synaptic vesicles in glycinergic The GlyT2 gene was inactivated in mouse E14 (129/OLA) nerve terminals, and the GlyT2 gene constitutes a candiembryonic stem cells by replacing a segment of 2.1 kb, date disease gene in human hyperekplexia patients.which contains the exon encoding the fourth transmembrane domain of the transporter, with a neomycin-resis-Introduction tance cassette (Figure 1A).By using standard transgenic and mouse breeding techniques, chimeric mice were Amino acids serve as neurotransmitters throughout the obtained and used to generate F1 offspring heterozyanimal kingdom.Glutamate is the predominant excitgous for GlyT2.These animals appeared phenotypically atory transmitter, and ␥-aminobutyric acid (GABA) and normal and showed undisturbed development and fertilglycine are the major inhibitory transmitters in the mamity.Intercrossing of the heterozygous mice generated malian CNS.The postsynaptic actions of these amino wild-type (ϩ/ϩ) as well as heterozygous (ϩ/Ϫ) and hoacids are terminated by specific ion-driven transporter mozygous (Ϫ/Ϫ) GlyT2 mutant mice, as determined by proteins, which mediate transmitter re-uptake into nerve Southern blot analysis (Figure 1B).terminals as well as glial cells (for review, see Amara and GlyT2 Ϫ/Ϫ newborn pups were obtained with the ex-Kuhar, 1993; Schloss et al., 1994; Nelson, 1998).Notably, pected Mendelian frequency, indicating that there was all amino acid transporters exist in different subtypes no increased embryonic mortality in the mutant mice.encoded by different genes, which often show a restricted RT-PCR experiments showed that GlyT2 mRNA was expression in either glia or neurons.This suggests that present in caudal regions of the CNS in wild-type mice, the functional roles of glial and neuronal transporters whereas no PCR product was obtained with mRNA exare distinct.tracted from GlyT2 Ϫ/Ϫ brain stem (Figure 1C).Thus, GlyT2 In an attempt to elucidate the in vivo functions of glial transcripts were absent in the homozygous mutants.Similarly, Western blot analysis with an antiserum raised