Adenosine deaminase (ADA, EC 3.5.4.4) is an essential enzyme of purine metabolism that is expressed at very high levels in the murine placenta where it accounts for over 95% of the ADA present at the fetal gestation site. We have recently shown that ADA-deficient fetuses, which also lack ADA in their adjoining placentas, die during late fetal development in association with profound purine metabolic disturbances and hepatocellular impairment. We have now investigated the potential importance of placental ADA by genetically restoring the enzyme to placentas of ADA-deficient fetuses. This genetic engineering strategy corrected most of the purine metabolic disturbances, prevented serious fetal liver damage, and rescued the fetuses from perinatal lethality. Our findings suggest that placental ADA is important for murine fetal development and illustrate a general strategy for the tissue specific correction of phenotypes associated with null mutations in mice.During mammalian development the first differentiation event gives rise to the trophectoderm, which in turn provides lineages for specialized extraembryonic cells known as trophoblasts. These cells make the physical connection between the embryo and the maternal environment and play important roles in the implantation process and placental function (1). Inadequate placental development is associated with a high incidence of early embryonic mortality (2-4) and serious pregnancy disorders such as preeclampsia (5). Although the formation of a functional placenta is essential for mammalian embryogenisis and fetal development, relatively little is known about the molecular mechanisms that govern trophoblast differentiation and subsequent function. Determining what proteins are produced in trophoblasts and elucidating their physiological roles is an important part of understanding how this cell lineage contributes to the formation of a functional placenta.One such protein that is highly abundant in the murine placenta is adenosine deaminase (ADA).1 ADA is an essential enzyme of purine metabolism that is expressed at very high levels in trophoblasts of the murine placenta (6, 7). The physiological importance of ADA in trophoblasts of the placenta is not known. However, recent evidence suggests that ADA is essential during fetal stages of development. ADA-deficient fetuses, which also lacked ADA in trophoblasts of their adjoining placentas, died perinatally in association with profound purine metabolic disturbances and hepatocellular impairment (8, 9). Considering that greater than 95% of ADA enzymatic activity found in the fetal gestation site resides in trophoblasts of the placenta, it is likely that placental ADA plays an essential role during fetal development. Here we show that genetically restoring ADA to placentas of ADA-deficient fetuses rescued them from perinatal lethality, thereby providing compelling evidence for the importance of placental ADA for fetal development.
MATERIALS AND METHODS
ADA Minigene Construction and Transgenic Mouse Generation-Theplasmid, Ϫ...