The miR-34 family of miRNAs (miR-34a, miR-34b, and miR-34c) are expressed mainly in the testis, brain, and lung. miR-34 proteins are induced upon p53 activation and are associated with tumor suppression, aging, neurodegeneration, and spermatogenesis. miR-34afl/fl mice possess loxP sites flanking the entire microRNA 34a (miR-34a) sequence. Homozygous miR-34afl/fl mice are viable and fertile. When bred to mice that express tissue-specific Cre recombinase, resulting offspring will have miR-34a sequence deleted in the cre-expressing tissues. When crossed to mice expressing CAG-cre, miR-34a-/- mice exhibit abnormal neuronal precursor proliferation. When cre recombined miR-34a-/- mice are bred to Mirc21-/- mice (Stock No. 018546), which are deficient in miR-34b and miR-34c, the double mutant mice lack all three miR-34 family members. These miR-34 KO mice show normal development with an intact p53 pathway.
