Regulation of poly(A) tail size of vasopressin mRNA.

Dehydration represents a strong stimulus for the secretory activity of hypothalamic vasopressinergic neurons and induces a sustained rise in hypothalamic [Arg8]vasopressin (AVP) mRNA. We now report that, in addition to the change in mRNA accumulation, this stimulus leads to an increase in the size of the mature AVP gene transcripts. Using Northern blot analysis in conjunction with internal RNA size markers, we demonstrate here that a 6-day period of salt imbibition induced a gradual size increase of AVP mRNA from 810 to a maximum of 930 bases. This change was fully reversed by day 30 following termination of the salt treatment. Any alteration of the mRNA capping or polyadenylation sites was ruled out by S1 mapping. However, poly(A) tail removal reduced AVP mRNA of all treatment groups to exactly the same size (600 bases). It is concluded that the dehydration-induced size change is due to a greater than 50% increase of the mean steady state length of the poly(A) tail. It remains to be determined to what extent the observed increase in poly(A) tail length may have an effect on AVP mRNA stability or translational efficiency.