ADH4‐lacZ Transgenic Mouse Reveals Alcohol Dehydrogenase Localization in Embryonic Midbrain/ Hindbrain, Otic Vesicles, and Mesencephalic, Trigeminal, Facial, and Olfactory Neural Crest

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Abstract
Pursuit of endogenous functions for various members of the alcohol dehydrogenase (ADH) enzyme family has led to exploration of gene expression patterns. Herein, we have used transgenic mice to examine the mouse gene encoding class IV ADH (ADH4), an enzyme that is weakly effective as an ethanol dehydrogenase, but highly effective as a retinol dehydrogenase in vitro. ADH4 promoter and upstream regulatory sequences were fused to lacZ and stably introduced into mice so that embryonic expression of ADH4 could be easily monitored by examination of β‐galactosidase activity in situ. Several independent founder mice carrying ADH4‐lacZ transgenes with either 2.7 or 9.0 kb of upstream regulatory sequences produced embryos in which expression was highly localized in the brain and craniofacial region at stages E8.5 to 9.5 during neurulation. Expression in the brain was limited to the ventral midbrain and its boundary with the hindbrain. At stage E8.5, ADH4‐lacZ expression was noticed in several dispersed regions throughout the head, and by stage E9.5 it was evident that these regions corresponded to the otic vesicles and migrating neural crest cells, particularly the mesencephalic, trigem‐inal, facial, and olfactory neural crest. ADH4‐lacZ expression in the trigeminal neural crest appeared as long fibers emanating from the midbrain/hindbrain boundary and extending to the first branchial arch following the tract of the trigeminal nerve. These findings support the hypothesis that ADH4 may normally function in retinoic acid synthesis needed for brain and neural crest development and that it participates in the mechanism of ethanol‐induced brain and craniofacial birth defects.