Hiroyuki Yoneshima

Scrambler and yotari disrupt the disabled gene and produce a reeler- like phenotype in mice

Formation of the mammalian brain requires choreographed migration of neurons to generate highly ordered laminar structures such as those in the cortices of the forebrain and the cerebellum. These processes are severely disrupted by mutations in reelin which cause widespread misplacement of neurons and associated ataxia in reeler mice,. Reelin is a large extracellular protein secreted by pioneer neurons that coordinates cell positioning during neurodevelopment,. Two new autosomal recessive mouse mutations, scrambler and yotari have been described that exhibit a phenotype identical to reeler. Here we report that scrambler and yotari arise from mutations in mdab1 (ref. 12), a mouse gene related to the Drosophila gene disabled ( dab ). Both scrambler and yotari mice express mutated forms of mdab1 messenger RNA and little or no mDab1 protein. mDab1 is a phosphoprotein that appears to function as an intracellular adaptor in protein kinase pathways. Expression analysis indicates that mdab1 is expressed in neuronal populations exposed to Reelin. The similar phenotypes of reeler, scrambler, yotari and mdab1 null mice indicate that Reelin and mDab1 function as signalling molecules that regulate cell positioning in the developing brain.

A novel neurological mutant mouse, yotari, which exhibits reeler-like phenotype but expresses CR-50 antigen/reelin.

We present yotari, a novel neurological mutant mouse whose mutation is transmitted in an autosomal recessive manner. The phenotype of yotari is very similar to that of reeler. yotari mutants are recognizable by their unstable gait and tremor and by their early deaths at around the time of weaning. The cerebella of homozygous yotari are hypoplastic and have no foliation. A molecular and a granular cell layer can be identified, but Purkinje cells are scattered throughout both the granular layer and white matter. The laminar structure of the cerebral cortex and the hippocampal formation are also distorted. To test whether the mutated gene in yotari is the reeler gene, reelin, yotari heterozygotes were mated with reeler homozygotes or heterozygotes. The absence of abnormal offspring indicated that the yotari gene is distinct from reelin. Furthermore, expression of mRNA and protein of reelin was verified by Northern blotting and immunohistochemistry using a CR-50 monoclonal antibody (mAb) which is specific to Reelin, the reelin gene product. Although the mutation of several genes, including cyclin-dependent kinase 5 (Cdk 5), p35 and LIS1, 45 kDa subunits of platelet-activating factor acetylhydrolase (PAF-AH) Ib, in Miller-Dieker lissencephaly syndrome (MDS) has been reported to cause abnormal laminar structure in the brain, no abnormality was found in yotari by Western blotting with antibodies (Abs) against these molecules. The close similarity of the phenotypes of yotari and reeler and the expression of reelin in yotari may suggest that the gene mutated in yotari encodes a molecule that is on the same signaling pathway as Reelin, the product of reelin. yotari will provide valuable clues to explore the molecular mechanism of neuronal migration and orderly laminar structure formation of the brain.

710 Yotari, a novel neurological mutation of mouse

Kazunori Sango’ , Shoji Yamanaka2, Richard L. Proia3, Shuji Inoue’ Tay-Sachs and Sandhoff diseases are clinically similar neurodegenerative disorders. These two sphingolipidoses are characterized by a heritable absence of &hexosaminidase A resulting in defective GM2 gangiioside degradation. Through disruption of the Hexa and Hexb genes in murine embryonic stem cells, we have established mouse models corresponding to each disease. Unlike the two human disorders, the two mouse models showed very different neurologic phenotypes. Although exhibiting biochemical and pathologic features of the disease, the Tay-Sachs model showed no neurological abnormalities. In contrast, the Sandhoff model showed profound neurologic disturbances with storage in brain that is increased in amount and distribution relative to the Tay-Sachs model. The phenotypic difference between the two mouse models is the result of differences in the ganglioside degradation pathway between mice and humans.

810 Morphological and neurological evaluations in mice lacking type 1 inositol 1,4,5-trisphosphate receptor (I)

809 Electrophysiological analysis of cerebellar Purkinje neuron in mice lacking type I inositol 1,4,5trisphosphate receptor (II). Takafumi Inoue’, Mineo Matsumoto”‘, Toshiyuki Nakagawa’, Eiichiro Nagata’, Kortaro Tanaka’, Maki Yamada’, Hiroyuki Yoneshima’, Atsushi Miyawaki’, Shinichi Sakakibara”4, Yasuo Fukuuchi’, Teiichi Furuichi’, Hideyuki Okano’V4, Tetsuo Noda3, Katsuhiko Mikoshiba’. Dept. of Molecular Neurobiology, Inst. Medical Science, Univ. of Tokyo’, Dept. of Neurology, Keio Univ. Sch. of Med.‘, Dept. of Cell Biology, Cancer Inst.3, Dept. of Molecular Neurobiology, Inst. of Basic Medical Sciences and Center of TARA, Univ. of Tsukuba4 The inositol 1,4,5trisphosphate (IP3) receptor acts as an IP3-gated Ca” release channel in a variety of cell types. Type 1 IP3 receptor (IP3Rl) is the major neuronal member of the IP3R family in the central nervous system, predominantly enriched in cerebellar Purkinje cells. We generated IP3Rl-deficient mice (IP3RL/-) by gene targeting to analyze the physiological function of IP3Rl. There was no abnormality in the haematoxylin-eosin staining pattern in the IP3Rl-/cerebellar cortex and Purkinje cells, though the IP3 binding and Ca2’ release activity of the cerebellum was apparently reduced. Electrophysiological measurements in the cerebellar slice from IP3Rl-/mice revealed that the unique electrophysiological properties of the Purkinje cell (e.g. Na and Ca spike complex, synaptic input from parallel and climbing fibers) were not severely impaired.

809 Electrophysiological analysis of cerebellar Purkinje neuron in mice lacking type I inositol 1,4,5-trisphosphate receptor (II)

809 Electrophysiological analysis of cerebellar Purkinje neuron in mice lacking type I inositol 1,4,5trisphosphate receptor (II). Takafumi Inoue’, Mineo Matsumoto”‘, Toshiyuki Nakagawa’, Eiichiro Nagata’, Kortaro Tanaka’, Maki Yamada’, Hiroyuki Yoneshima’, Atsushi Miyawaki’, Shinichi Sakakibara”4, Yasuo Fukuuchi’, Teiichi Furuichi’, Hideyuki Okano’V4, Tetsuo Noda3, Katsuhiko Mikoshiba’. Dept. of Molecular Neurobiology, Inst. Medical Science, Univ. of Tokyo’, Dept. of Neurology, Keio Univ. Sch. of Med.‘, Dept. of Cell Biology, Cancer Inst.3, Dept. of Molecular Neurobiology, Inst. of Basic Medical Sciences and Center of TARA, Univ. of Tsukuba4 The inositol 1,4,5trisphosphate (IP3) receptor acts as an IP3-gated Ca” release channel in a variety of cell types. Type 1 IP3 receptor (IP3Rl) is the major neuronal member of the IP3R family in the central nervous system, predominantly enriched in cerebellar Purkinje cells. We generated IP3Rl-deficient mice (IP3RL/-) by gene targeting to analyze the physiological function of IP3Rl. There was no abnormality in the haematoxylin-eosin staining pattern in the IP3Rl-/cerebellar cortex and Purkinje cells, though the IP3 binding and Ca2’ release activity of the cerebellum was apparently reduced. Electrophysiological measurements in the cerebellar slice from IP3Rl-/mice revealed that the unique electrophysiological properties of the Purkinje cell (e.g. Na and Ca spike complex, synaptic input from parallel and climbing fibers) were not severely impaired.