myo-
Inositol is an essential biomolecule that is synthesized by
myo-inositol monophosphatase (
IMPase) from
inositol monophosphate species. The enzymatic activity of
IMPase is inhibited by
lithium, a
drug used for the treatment of mood swings seen in
bipolar disorder. Therefore, myo-
inositol is thought to have an important role in the mechanism of
bipolar disorder, although the details remain elusive. We screened an ethyl nitrosourea mutant mouse library for
IMPase gene (
Impa) mutations and identified an Impa1 T95K missense mutation. The
mutant protein possessed undetectable enzymatic activity. Homozygotes died perinatally, and E18.5 embryos exhibited striking developmental defects, including hypoplasia of the mandible and asymmetric fusion of ribs to the sternum. Perinatal lethality and morphological defects in homozygotes were rescued by dietary myo-
inositol. Rescued homozygotes raised on normal
drinking water after weaning exhibited a hyper-locomotive trait and prolonged circadian periods, as reported in rodents treated with
lithium. Our mice should be advantageous, compared with those generated by the conventional gene knock-out strategy, because they carry minimal genomic damage, e.g. a point mutation. In conclusion, our results reveal critical roles for intracellular myo-
inositol synthesis in craniofacial development and the maintenance of proper brain function. Furthermore, this mouse model for cellular
inositol depletion could be beneficial for understanding the molecular mechanisms underlying the clinical effect of
lithium and myo-
inositol-mediated skeletal development.