Effect of estrogen on gene expression in the chick oviduct. Effect of estrogen on the sequence and population complexity of chick oviduct poly(A) containing RNA

Total cellular RNA preparations were isolated from chicken oviducts at three different development stages: (a) immature chicks which were chronically stimulated with estrogen; (b) estrogen stimulated chicks which were then withdrawn from hormone for 12 days; and (c) laying hens. Total cellular RNA containing 3' poly(A) sequences (poly(A) RNA) were then isolated from these preparations using oligo(dT) cellulose chromatography. The number average nucleotide length of the poly(A) RNA preparations in each case was 2000 nucleotides. The number average nucleotide length of the poly(A) residues at the 3' terminal end of each RNA preparation was approximately 70 adenylate residues. Complementary DNA (cDNA) copies to each preparation of poly(A) RNA were synthesized using avian myeloblastosis virus RNA directed DNA polymerase. These cDNA(poly)(A) preparations were then utilized in DNA excess hybridization experiments to analyze the complexity of the DNA sequences from which these RNAs were transcribed. Approximately 22% of each of the total cellular poly(A) RNAs were transcribed from repeated DNA sequences (average repeat frequency of 35 copies/genome) while the remaining majority were transcribed from single copy or unique sequence DNA. It was possible to estimate the number of different poly(A) RNA sequences per cell by analyzing the kinetics of hybridization of these cDNA(poly)(A) preparations to total cellular poly(A) RNA extracts under conditions of RNA excess. The results revealed that 41% of the poly(A) RNA from laying hen oviduct consisted of, on the average, three different sequences/cell, each of which was present in approximately 25,000 copies/cell. The remainder of the poly(A) RNA in this tissue consisted of approximately 25,000 different sequences/cell, which were present largely in only two or three copies/cell. A somewhat similar sequence complexity was found for oviduct cells prepared from estrogen stimulated chicks. We estimated that there were approximately 20,000 different poly(A) RNA sequences/cell, each represented in only one to two copies/cell. However, there were five sequences which were present, on the average, in a concentration of 5600 copies/cell. The poly(A) RNAs from hormone withdrawn tissue, on the other hand, had a lower sequence complexity. There were only approximately 10,000 different poly(A) RNA sequences/cell, each present in about three copies/cell. Furthermore, the few sequences present in a great abundance in hen and hormone stimulated tissues were apparently absent in oviduct tissue from hormone withdrawn chicks, suggesting that the intracellular concentrations of these high frequency RNA sequences are dependent on estrogen.