Volume 17, Number 2,
Issue of January 15, 1997
pp. 635-645
Copyright ©1997 Society for Neuroscience
The Type 1 Inositol 1,4,5-Trisphosphate Receptor Gene Is Altered
in the opisthotonos Mouse
Received Aug. 28, 1996; revised Oct. 21, 1996; accepted Nov. 5, 1996.
Valerie A. Street1,
Martha M. Bosma1,
Vasiliki
P. Demas1,
Melissa R. Regan2,
Doras D. Lin2,
Linda C. Robinson1,
William S. Agnew2, and
Bruce L Tempel1
1 Departments of Otolaryngology and Pharmacology,
University of Washington School of Medicine, Seattle, Washington 98195, and Geriatric Research Education and Clinic Center, Veterans Affairs
Puget Sound Health Care System, Seattle, Washington 98108, and
2 Department of Physiology, The Johns Hopkins University
School of Medicine, Baltimore, Maryland 21205
The opisthotonos (opt) mutation arose
spontaneously in a C57BL/Ks-db2J colony and is the only
known, naturally occurring allele of opt. This mutant
mouse was first identified based on its ataxic and convulsive
phenotype. Genetic and molecular data presented here demonstrate that
the type 1 inositol 1,4,5-trisphosphate receptor (IP3R1)
protein, which serves as an IP3-gated channel to release calcium from intracellular stores, is altered in the opt
mutant. A genomic deletion in the IP3R1 gene removes two
exons from the IP3R1 mRNA but does not interrupt the
translational reading frame. The altered protein is predicted to have
lost several modulatory sites and is present at markedly reduced levels
in opt homozygotes. Nonetheless, a strong calcium
release from intracellular stores can be elicited in cerebellar
Purkinje neurons treated with the metabotropic glutamate receptor
(mGluR) agonist quisqualate (QA). QA activates Group I mGluRs linked to
GTP-binding proteins that stimulate phospholipase C and subsequent
production of the intracellular messenger IP3, leading to
calcium mobilization via the IP3R1 protein. The calcium
response in opt homozygotes shows less attenuation to
repeated QA application than in control littermates. These data suggest
that the convulsions and ataxia observed in opt mice may
be caused by the physiological dysregulation of a functional IP3R1 protein.
Key words:
opisthotonos;
seizures;
genomic deletion;
Purkinje neurons;
inositol 1,4,5-trisphosphate receptor;
metabotropic
glutamate receptor;
quisqualate;
mouse chromosome 6;
alternative
splicing