New insights into the physiological actions of selenoproteins from genetically modified mice.

Selenium (Se) is an essential trace element in mammals. Dietary Se restriction or conditions of Se malabsorption lead to deficiency syndromes or exacerbate established diseases in humans and in many animal models. It is assumed that most, if not all, physiological actions of Se are mediated by selenocysteine (Sec) containing proteins. However, the exact role of particular selenoproteins for certain molecular pathways, for the metabolism of nutrients, hormones or cellular components and for the development and adaptive responses of the organism have often remained elusive. Through the use of transgenic animals, it becomes increasingly feasible to interfere specifically with the expression of single selenoproteins in certain tissues or at certain times. While some transgenic animals exhibit phenotypes that were expected from biochemical studies, in other instances the observed effects were a surprise in view of earlier hypotheses.