Accumulation of winter flounder antifreeze messenger RNA after hypophysectomy.

The effect of hypophysectomy (hypex) on winter flounder antifreeze mRNA accumulation in the liver was examined. Hypophysectomy resulted in a significant decrease in serum freezing temperature, and increases in liver weights, total liver poly(A)+ RNA and antifreeze polypeptides (AFP) mRNA accumulation. The identity of the AFP mRNA in hypex animals was confirmed by gel electrophoresis, cell-free translation, and Northern blot hybridization techniques. Cytoplasmic dot hybridization analysis indicated that the AFP mRNA level in hypex fish approximated that observed in winter animals actively synthesizing AFP. An increase in AFP mRNA was detectable as early as the first day after hypophysectomy and by Day 7 reached 25% of the level found in fish actively synthesizing AFP mRNA during the winter months. Since AFP mRNA is found at very low levels in the control flounder, we suggest that its accumulation after hypophysectomy depends on accelerated transcription. The pituitary gland appears to regulate the liver AFP mRNA level by a negative transcriptional control mechanism.