Regulation of placental efficiency for nutrient transport by imprinted genes.

Intrauterine growth and development can impact upon the long-term health of an individual. The fetus is dependent upon the placenta for its supply of nutrients and oxygen from the mother. In turn, the functional capacity of the placenta to supply that demand is under the control of the fetal and maternal genomes. Recent evidence suggests that imprinted genes, a class of genes found in placental mammals whose expression depends on their parental origin, have multiple roles in the placenta. The imprinted genes regulate the growth and transport capacity of the placenta, thereby controlling the supply of nutrients. They may also regulate the growth rate of fetal tissues directly, thereby controlling nutrient demand by the fetus. Recent studies using mice with deletions or disruption of imprinted genes with an altered balance between placental and fetal growth and changes in placental efficiency are indicative of feto-placental signalling of fetal nutrient demand. We propose that signalling mechanisms involving growth demand signals and nutrient transporters are likely to occur and are important for fine tuning normal fetal growth.