Disruption of the mouse inositol 1,3,4,5,6-pentakisphosphate 2-kinase gene, associated lethality, and tissue distribution of 2-kinase expression

Many functions have been suggested for inositol 1,2,3,4,5,6- hexakisphosphate (InsP₆), including mRNA export, nonhomologous end-joining, endocytosis, and ion channel regulation. However, it remains to be demonstrated that InsP₆ is necessary for in vivo survival. We previously isolated a cDNA encoding the mammalian inositol 1,3,4,5,6- pentakisphosphate (InsP₅) 2-kinase (2-kinase), the enzyme that converts InsP₅ to InsP₆. We used the sequence to search the BayGenomics databases and identify an ES cell line (XA232) that has a gene trap construct embedded in the 2-kinase gene. We obtained a mouse from this line, produced heterozygotes, and confirmed that the heterozygotes contain the trapping construct and have diminished 2-kinase activity. Breeding the XA232 heterozygotes produced no homozygous offspring; thus, loss of 2-kinase is lethal in mice. Dissections of embryonic day-8.5 uteri yielded no homozygous embryos; thus, the mice die before day 8.5 postcoitum. The gene trap construct contains a β-galactosidase/neomycin reporter gene, allowing us to stain heterozygotes for β-galactosidase to determine tissue-specific expression of 2-kinase protein. 2-kinase is expressed in the hippocampus, the cortex, the Purkinje layer of the cerebellum in the brain, in cardiomyocytes, and in the testes of adult mice. At day 9.5 postcoitum, 2-kinase was expressed in the notochord, the ventricular layer of the neural tube, and the myotome of the somites. Intense staining was also seen in the yolk sac, suggesting that InsP₆ is necessary for yolk sac development or function. Furthermore, failure of yolk sac development or function is consistent with the early lethality of 2-kinase embryos.