Mice with a Targeted Disruption of the Voltage-Dependent Calcium Channel Gene, Cacng4.
Abstract number :
3.026
Submission category :
Year :
2001
Submission ID :
804
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
V.A. Letts, PhD, The Jackson Laboratory, Bar Harbor, ME; C.L. Mahaffey, MS, The Jackson Laboratory, Bar Harbor, ME; W.N. Frankel, PhD, The Jackson Laboratory, Bar Harbor, ME
RATIONALE: The stargazer (stg/stg) and waggler (stgwag/ stgwag) mice have mutations in the voltage-dependent calcium channel gamma subunit gene, Cacng2. Noticeably these mice have absence seizures throughout their lives. There are many other related gamma subunits genes, several of which are predominantly expressed in the brain. If these genes are disrupted, do they also cause absence epilepsy in mice? To pursue this question we have made a targeted disruption of the Cacng4 gene.
METHODS: The Cacng4 gene was disrupted by replacing exon 4 encoding the carboxy terminus of the protein with a DNA cassette including the lacZ gene. This disruption was introduced into mice using standard knockout technology and homozygous mice for the targeted disruption were studied. EEGs were measured from bipolar electrodes implanted into each cortical hemisphere. Recordings were taken daily over a three hour interval.
RESULTS: The homozygous mice carrying both targeted alleles of Cacng4 were overtly normal. EEG recordings from these mice reveal that they have no significant absence seizure activity. We have now set up crosses between these mice and both wagglers and stargazers to introduce the Cacng4 targeted disruption onto the Cacng2 mutant background. On measuring the absence seizure activity in the double homozygotes generated from waggler and Cacng4, we noticed that the activity was markedly enhanced in the double mutant compared to the waggler mutation alone. Interestingly we have been unable to produce any stargazer Cacng4-/- double mutants.
CONCLUSIONS: Although mice with Cacng4 targeted disruptions are viable and lack absence seizure activity, the combination of this mutation with the Cacng2 disruptions does exacerbate the original Cacng2 absence seizure phenotype, as observed in the waggler Cacng4-/- double homozygous mice. Stargazer seizures are more frequent and of longer duration than waggler, indicating that the stargazer mutation in the Cacng2 gene generates a more pronounced seizure phenotype in this mouse, and the effect of introducing the Cacng4 disruption onto the stargazer background is so severe that these double homozygous mice appear to be inviable.
Support: NIH NS32801.