The protein encoded by Brsk2 is a serine/threonine-protein kinase that is involved in neuronal polarization, axon specification, axon branching, and presynaptic differentiation in diverse neuronal populations. These mice possess loxP sites on either side of exon 1 of the targeted gene. Mice that are homozygous for the targeted mutation are viable and fertile, with no overt phenotype. When these mutant mice are bred to mice that express Cre recombinase, resulting offspring will have exon 1 deleted in the cre-expressing tissues. When crossed to Brsk1 knock out mice (Stock No.023198), and mice expressing Cre recombinase in neurons, the resulting double null homozygotes die shortly after birth due to respiratory failure.