Differential polyadenylation of the mutant vasopressin mRNA during development of Brattleboro rats.

In the normal (Wistar) rat vasopressin encoding mRNA first appears at embryonic day 15 as demonstrated by in situ hybridization of hypothalamic sections. In mutant (Brattleboro) rats, which possess a defective vasopressin gene with a single nucleotide deletion, the corresponding transcript is not detectable before fetal day 18. In both rat strains however expression of the structurally related oxytocin gene begins at fetal day 19. Whereas normal and mutant vasopressin encoding mRNAs are identical in size up to at least three weeks after birth, the corresponding transcripts from adult Brattleboro but not from normal rats are markedly larger. This increase in size is due to a longer stretch of poly(A) sequence as demonstrated by treatment of the respective mRNAs with RNase H and oligo(dT). Thus the mutant vasopressin gene transcript is subject to a cellular-specific differential polyadenylation process during development.