A new mutation that causes severe epilepsy in mice (July 1998)

Researchers in the Mammalian Genetics and Development Section have shown that mutagenesis within a large complex of nested, radiation-induced deletions at the pink-eyed dilution (p) locus in mouse chromosome 7 causes single-gene mutations that result in severe epilepsy. Mice that carry a long, proximally-extending homozygous-lethal p deletion, p46DFiOD, were mated to the progeny of males treated with N-ethyl-N-nitrosourea (ENU), and the offspring were observed for abnormal phenotypes. ENU is a highly efficient mutagen in mouse spermatogonial stem cells, and is known to induce single base-pair changes. Among the offspring were two independently generated mutations, 723SJ and 1060SJ, that cause profound and nearly constant seizures, runting, and juvenile lethality. Seizures are so severe that death usually occurs between the ages of 15 and 18 days. Interestingly, mice that carry only a single mutant copy (the mice with seizures carry two mutant copies) of this gene appear to be normal, but manifest significant hyperactivity as measured by open-field activity behavioral testing. Mice that carry one 723SJ mutation and one 1060SJ mutation have the severe seizures, so that the two are probably different mutations in the same gene.

The strategy of researchers in the Mammalian Genetics and Development Section is designed to positionally clone the gene responsible for this psr ("profound seizures and runting") phenotype. They are isolating a series of DNA clones that span that the minimal deletion interval that must contain a least part of the psr gene, and will obtain the DNA sequence from that clone set. By comparing the normal DNA sequence of genes within the clone set to the DNA sequences from the 723SJ and 1060SJ mutations, it can be determined which coding region has suffered the ENU-induced changes. This segment on mouse 7 that includes psr is probably conserved on human chromosome 11p14, so the possibility that some form of human epilepsy is caused by similar mutations in 11p14 will be examined. Diagnostic tests on tissue and blood samples from the mutant mice are being performed in ORNL’s Phenotype Screening Center to discover any biochemical abnormalities associated with the seizures. Researchers working on this project include Lisa S. Webb, Gary A. Sega (I&C Division), Eugene M. Rinchik, and Dabney K. Johnson.

Contact: Dabney K. Johnson
Phone: 574-0953
E-mail: k29@ornl.gov