Vitamin A (retinol) must be metabolized to an active retinoid ligand in order to fulfill all of its roles in vertebrate development. During retinoid signaling retinol is first converted to retinal followed by conversion of retinal to the active ligand retinoic acid which modulates nuclear retinoic acid receptors. The alcohol dehydrogenase (ADH) enzyme family may function in the metabolism of retinol, the alcohol form of vitamin A, as well as ethanol metabolism. Some members of the ADH family prefer retinol as a substrate over ethanol, and the ability to oxidize retinol is competitively inhibited by intoxicating levels of ethanol. Likewise, there exists an aldehyde dehydrogenase (ALDH) family containing members preferring retinal, the aldehyde form of vitamin A, as a substrate over acetaldehyde. The spatiotemporal expression patterns of mouse ADHs and ALDHs overlap, suggesting that these enzymes may cooperate to upregulate retinoic acid synthesis during development. Retinoic acid synthesis may be decreased by excess ethanol consumption due to the ability of ethanol to act as a competitive inhibitor of ADH-catalyzed retinol oxidation. This suggests a mechanism whereby ethanol damage may occur during alcohol abuse. Treatment of mouse embryos at the neurulation stage with an intoxicating amount of ethanol leads to a reduction in retinoic acid levels, thus suggesting ADH participates in the retinoic acid synthetic pathway. This may be a contributing factor in fetal alcohol syndrome, characterized by malformations of neural and craniofacial tissues known to require retinoic acid for proper development. The in vitro properties and gene expression profiles of the ADH and ALDH enzyme families suggest a role in both alcohol and retinol metabolism, but there is a need for genetic loss-of-function studies in mice to address their true physiological roles. The mouse ADH gene family consists of three classes (ADH-I, ADH-III, and ADH-IV), with only ADH-I and ADH-IV known to oxidize retinol in vitro. The extent of the mouse ALDH gene family is unknown, but ALDH-I has been shown to oxidize retinal in vitro and has an expression pattern overlapping that of ADH-I and ADH-IV. Mutational analysis of all three mouse ADHs and ALDH-I is proposed here. Goals: (1) Complete the genetic analysis of ADH now in progress by preparing mice carrying knockout mutations of ADH-I, ADH-III, and ADH-IV, as well as mice carrying mutations of multiple ADHs since redundancy of function is suspected. (2) Analyze the phenotype of mice carrying mutations in single or multiple ADH genes for morphological defects during development and adulthood, for the ability to metabolize ethanol and retinol, and for the ability to survive and reproduce during vitamin A deficiency. (3) Prepare and ALDH-I knockout mouse plus mice mutated for one or more ADHs and ALDH-I, then analyze their phenotype as above.
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