Vitamin A-sensitive tissues in transgenic mice expressing high levels of human cellular retinol-binding protein type I are not altered phenotypically

The suggested function of cellular retinol-binding protein type I [CRBP(I)I is to carry retinol to esterifying or oxidizing enzymes. The retinyl ester s are used in storage or transport, whereas oxidized forms such as all-tran s or 9-cis retinoic acid are metabolites used in the mechanism of action of vitamin A. Thus, high expression of human CRBP(I) [hCRBP(I)] in transgenic mice might be expected to increase the production of retinoic acid in tiss ues, thereby inducing a phenotype resembling vitamin A toxicity. Alternativ ely, a vitamin A-deficient phenotype could also be envisioned as a result o f an increased accumulation of vitamin A in storage cells induced by a high hCRBP(I) level. Signs of vitamin A toxicity or deficiency were therefore e xamined in tissues from transgenic mice with ectopic expression of hCRBP(I) . Testis and intestine, the tissues with the highest expression of the tran sgene, showed normal gross morphology.: Similarly, no abnormalities were ob served in other tissues known to be sensitive to vitamin A status such as c ornea and retina, and the epithelia in the cervix, trachea and-skin. Furthe rmore, hematologic variables known to be influenced by vitamin A status suc h as the hemoglobin concentration, hematocrits and the number of red blood cells were within normal ranges in the transgenic mice. In conclusion, thes e transgenic mice have normal function of vitamin A despite high expression of hCRBP(I) in several tissues.