En2-cre line 22 transgenic mice (also called En2cre-22, En2cre line Tg22, or En2-cre tg-22) are viable and fertile, with expression of Cre recombinase directed to the embryonic midbrain-hindbrain constriction region by mouse engrailed 2 promoter/enhancer elements. Specifically, whole-mount RNA in situ hybridization with a Cre recombinase antisense probe shows cre expression in a narrow dorsal domain surrounding the midbrain-hindbrain junction at embryonic day 9.5 (E9.5). When these En2-cre line 22 transgenic mice are bred with mice containing loxP-flanked sequences, Cre-mediated recombination will result in deletion of the floxed sequences in a subset of En2-expressing tissues of the offspring; including the embryonic midbrain-hindbrain (mesencephalon-metencephalon) constriction region of the developing brain that gives rise to the posterior midbrain and medial cerebellum.
When the donating investigator bred En2-cre line 22 transgenic mice with lacZ reporter mice, adult brain regions in the double transgenic offspring showed evidence of embryonic Cre recombinase activity; these include a) part of the midbrain structure responsible for visual processing (superior colliculus), much of the region responsible for auditory processing (inferior colliculus), and some regions responsible for homeostatic and reflexive pathways (tegmentum); b) some anterior hindbrain structures responsible for integration of sensory perception, coordination and motor control (primarily the medial cerebellum); and c) forebrain structures responsible for short term memory and spatial navigation (hippocampus).
