Phenotypic Characterization and Brain Structure Analysis of Calcium Channel Subunit αδ-2 Mutant (Ducky) and αδ Double Knockout Mice

Auxiliary αδ subunits of voltage-gated calcium channels modulate channel trafficking, current properties, and synapse formation. Three of the four isoforms (αδ-1, αδ-2, and αδ-3) are abundantly expressed in the brain; however, of the available knockout models, only αδ-2 knockout or mutant mice display an obvious abnormal neurological phenotype. Thus, we hypothesize that the neuronal αδ isoforms may have partially specific as well as redundant functions. To address this, we generated three distinct αδ double knockout mouse models by crossbreeding single knockout (αδ-1 and -3) or mutant (αδ-2/ducky) mice. Here, we provide a first phenotypic description and brain structure analysis. We found that genotypic distribution of neonatal litters in distinct αδ-1/-2, αδ-1/-3, and αδ-2/-3 breeding combinations did not conform to Mendel's law, suggesting premature lethality of single and double knockout mice. Notably, high occurrences of infant mortality correlated with the absence of specific αδ isoforms (αΔ-2 > αδ-1 > αδ-3), and was particularly observed in cages with behaviorally abnormal parenting animals of αδ-2/-3 cross-breedings. Juvenile αδ-1/-2 and αδ-2/-3 double knockout mice displayed a waddling gate similar to ducky mice. However, in contrast to ducky and αδ-1/-3 double knockout animals, αδ-1/-2 and αδ-2/-3 double knockout mice showed a more severe disease progression and highly impaired development. The observed phenotypes within the individual mouse lines may be linked to differences in the volume of specific brain regions. Reduced cortical volume in ducky mice, for example, was associated with a progressively decreased space between neurons, suggesting a reduction of total synaptic connections. Taken together, our findings show that αδ subunits differentially regulate premature survival, postnatal growth, brain development, and behavior, suggesting specific neuronal functions in health and disease.