Species specificity and developmental patterns of expression of the beta amyloid precursor protein (APP) gene in brain, liver and choroid plexus in birds.

1. Human APP cDNA hybridized to a 3.5 kb mRNA in liver and brain RNA from chickens, pigeons, quail and ducks as well as in RNA from choroid plexus of chicken and quail. In contrast to all other species hitherto examined a 1.6 kb mRNA hybridizing to APP cDNA was found in abundant amounts in RNA from chicken and quail livers. 2. In the chicken, before hatching, the levels of APP mRNA in total RNA from liver and choroid plexus were higher than those in RNA from liver and choroid plexus of adults. However, RNA from the rest of the brain of chicken embryos contained less APP mRNA than RNA from brain of adults. 3. In the chicken, between 10 and 40 days after hatching, APP mRNA levels in RNA from liver were higher than adult levels, APP mRNA levels in RNA from choroid plexus were similar to adult levels and APP mRNA levels in RNA from the rest of brain were below the adult levels.