Actl6b (actin-like 6B; also known as BAF53b) is an actin-related protein that is embryonically expressed in neurons. The protein is part of a brain-specific complex that influences chromatin remodeling, gene expression, and dendritic outgrowth.
These targeted mutation mice carry a knockout allele that eliminates ACTL6B expression. Homozygous mice lacking the protein develop normally in utero, are born at predicted Mendelian frequencies, and appear indistinguishable from their littermates at birth. It is reported, however, that on a mixed 129 and C57BL/6 genetic background, roughly 25% of homozygous pups survive beyond postnatal day 2 and about 12% survive to adulthood. Removal of heterozygous and wildtype sibling pups from litters born to heterozygous or wildtype females is recommended to encourage the survival of homozygous pups. Although fertile, homozygous females fail to care for their young.
Morphologically, the brains of newborn homozygous pups appear grossly normal. Cultured embryonic hippocampal neurons show significantly shorter and less complex dendritic trees than controls. There is also a corresponding reduction in synapse number. Axonal myelination is impaired in postnatal brains. Behaviorally, homozygous adult mice are hyperactive.
