Expression of the genes for transthyretin, cystatin C and β A4 amyloid precursor protein in sheep choroid plexus during development

The levels of mRNA for transthyretin, cystatin C, and β A4 amyloid precursor protein were measured in the choroid plexus of sheep embryos during different stages of development, using specific cDNA probes and Northern blot analysis. The 3 different mRNAs were detectable in the brain of very young embryos with a crown-rump length of 1 cm, corresponding to only a few days of gestation. The choroid plexus increased in weight very rapidly in the first half of gestation and much more slowly in the second half. The level of transthyretin mRNA in choroid plexus increased during the first half of gestation and stayed constant thereafter until birth, at a level of about 70% of that in choroid plexus of adult sheep. The proportion of mRNA for the proteinase inhibitor cystatin C in total RNA from choroid plexus increased throughout gestation to adult levels at birth. The concentration of the mRNA for β A4 amyloid precursor protein in choroid plexus early in development was already as high as in adults and remained at this level throughout gestation. Messenger RNA for cystatin C or mRNA for β A4 amyloid precursor protein was not detected in adult sheep liver.