Transthyretin expression evolved more recently in liver than in brain

1. Transthyretin was found to be synthesized and secreted by choroid plexus from rats, echidnas, and lizards, but not toads. 2. Transthyretin was observed in blood from placental mammals, birds, and marsupials, but not reptiles and monotremes. 3. The obtained data suggest that transthyretin synthesis by the liver evolved independently in the lineage leading to the placental mammals and marsupials and in that leading to the birds. 4. It is proposed that transthyretin gene expression in mammalian liver appeared about 200 million years later than its first occurrence in the choroid plexus of the stem reptiles.