Occurrence of 2-5A and RNA degradation in the chick oviduct during rapid estrogen withdrawal

Abstract

Rapid withdrawal of estrogen from immature chicks, previously stimulated with the hormone, results in the inhibition of transcription of mRNAs of egg white proteins, rapid degradation of existing estrogen-induced mRNAs of egg white proteins, and decline in ribosomes and weight of the oviduct. On rapid withdrawal of estrogen, ovalbumin mRNA decreased to 65% after 3 h and was not detected after 24 h. In contrast to ovalbumin mRNA, cellular RNA content remained unchanged at 3 h and subsequently decreased to 51% of the stimulated value by 48 h. To study the mechanism of rapid degradation of RNA during estrogen withdrawal, the role of 2-5A- [px(A2''p)nA; x = 2 or 3, n .gtoreq. 2] dependent RNAse was investigated. The effect of 2-5A-dependent RNase on the stability of RNA in vitro was determined by incubating oviduct polysomes with 2-5A-dependent RNase and exogenous 2-5A. Ovalbumin mRNA was degraded more rapidly than .beta.-actin mRNA and rRNA, and the kinetics of RNA degradation were very similar to those observed in vivo. Levels of 2-5A in the chick oviduct increased shortly after estrogen withdrawal. Analysis of the oviduct RNA revealed that a distinct 18S rRNA derived fragment, 450 nucleotides in length, increased at 6 h after withdrawal and at subsequent time points when significant degradation of total cellular RNA was occurring. The 18S rRNA derived degradation product observed in vivo from the chick oviduct had the same mobility in denaturing agarose gels as the 18S rRNA cleavage product liberated on incubation of isolated oviduct ribosomes with purified 2-5A-dependent RNAse and exogenous 2-5A. These results indicate that in the chick oviduct 2-5A-dependent RNase is activated and may be involved in the degradation of mRNA and rRNA during estrogen withdrawal.