Oxytocin mRNA: increase of polyadenylate tail size during pregnancy and lactation.

Earlier studies indicate that rat hypothalamic oxytocin (OT) mRNA accumulation rises gradually during pregnancy and remains elevated throughout the lactation period. Here we show that, in addition, hypothalamic OT mRNA undergoes a structural change during this period. On gel electrophoresis, the size of rat OT mRNA increased from 750 bases (control) to a maximum of 820 bases (7th day of lactation). Removal of the poly(A) tail by the RNase H methods revealed that this size increase can be fully accounted for by a prolongation of the polyadenylate tail. There is considerable evidence for a role of the poly(A) tail segment in augmenting mRNA stability and, possibly, translational efficiency. It is thus conceivable that the demonstrated regulation of OT mRNA poly(A) tail length represents an additional level of OT gene control during pregnancy and lactation.