Effect of estrogen on gene expression in the chick oviduct. I. Deoxyribonucleic acid--deoxyribonucleic acid renaturation studies

DNA sequence organisation in avian genomes

By means of renaturation kinetics of DNA of the three avian species Cairina domestica, Gallus domesticus and Columba livia domestica the following major DNA repetition classes were observed: a very fast reannealing fraction comprising about 15% of the DNA, a fast or intermediate reannealing fraction that makes up 10%, and a slow reannealing fraction of about 70%, which apparently renatures with single copy properties. --Comparing the reassociation behaviour of short (0.3 kb) and long (greater than 2 kb) DNA fragments of duck and chicken it becomes apparent that only 12% (duck) and 28% (chicken) of the single copy DNA are interspersed with repetitive elements on 2 to 3 kb long fragments. The lengths of the repetitive sequences were estimated by optical hyperchromicity measurements, by agarose A-50 chromatography of S1 nuclease resistant duplexes and by electron microscopic measurements of the S1 nuclease resistant duplexes. It was found that in the case of the chicken DNA the single copy sequences alternating with middle repetitive ones are at least 2.3 kb long; the interspersed moderate repeats have a length average of at least 1.5 kb. The sequence length of the moderate repeats in duck DNA is smaller. The results show that the duck and the chicken genomes do not follow the short period interspersion pattern of genome organisation, characteristic of the eucaryotic organisms studied so far.

Quantitation of casein messenger ribonucleic acid sequences using a specific complementary DNA hybridization probe

Two highly purified rat casein mRNA fractions were used as templates to synthesize complementary DNA (cDNA) hybridization probes using RNA-directed DNA polymerase isolated from avian myeloblastosis virus. Both of the probes selectively hybridized to RNA isolated from lactating mammary tissue, but not to poly(adenylic acid)-containing rat liver RNA. An analysis of the kinetics of hybridization of the cDNA derived from the 15S casein mRNA (cDNA12S) with their individual mRNA templates indicated that greater than 90% hybridization occurred over a R0t range of one and one-half logs with R0t 1/2 values of 0.0023 and 0.0032 mol s l.-1, respectively. Compared with the total RNA isolated from lactating mammary tissue, these values represented a 166- and 245-fold purification, respectively, of these individual mRNA fractions. Using the 15S casein mRNA as a template, two probes of different lengths and specific activities were synthesized. The deoxyribonucleotide and mRNA concentrations and the temperature of incubation were optimized to obtain either a high specific activity cDNA probe, 330 nucleotides long, which represented approximately 25% of the mRNA or a lower specific activity preparation containing some complete cDNA copies, 1300 nucleotides in length. The Tm of the longer cDNA15S-15S mRNA hybrid was 88.5 degrees C, while that of the short cDNA15S-RNA hybrid was 82.5 degrees C. Following this initial characterization, the cDNA15S probe was utilized for three separate determinations: (1) Analysis of the sequence divergence between mouse and rat casein mRNAs. It was observed that the rate of hybridization of heterologous rat cDNA15S-mouse casein mRNA was only 20% that of the homologous rat cDNA15S-rat casein mRNA hybridization. The resulting heterologous hybrid displayed approximately 17% mismatching compared with the homologous hybrid. (2) Determination of the gene dosage for casein mRNA in normal and malignant mammary cells. In this study, an analysis of the kinetics of hybridization of the high specific activity cDNA15S probe with an excess of DNA isolated from lactating mammary tissue, carcinogen-induced mammary tumors, or rat liver indicated that casein mRNA was transcribed from the nonlification or deletion was observed during tumor formation or the process of mammary differentiation. (3) Quantitation of casein mRNA sequences during normal mammary gland development. RNA excess hybridizations were performed using RNA extracted from either pregnant, lactating, or regressed rat mammary tissue. The concentration of casein mRNA molecules/alveolar cell was found to increase 12-fold from 5 days of pregnancy until 8 days of lactation and then declined to approximately 2% of the maximal level of 79 000 molecules/cell by 7 days after weaning. A coordinate increase was observed in casein mRNA sequences detected by cDNA hybridization and mRNA activity measured in a cell-free translation assay.

Studies on the structure and function of chick-oviduct chromatin. 1. Fractionation by ECTHAM-cellulose chromatography and physico-chemical characterization

Chick oviduct chromatin was separated into a ribonucleoprotein fraction and two chromatin fractions (early and late eluting). We utilized a gentle procedure in which moderately hydrated chromatin was subjected to chromatography on a weak ionic-exchange resin (ECTHAM-cellulose) eluted with a combined pH-salt gradient. Chemical analysis of the early (fraction I) and late (fraction II) eluting fractions revealed that their histones were identical and their nonhistone proteins were markedly different. Control experiments showed that these differences were not due to protein rearrangements during chromatin preparation and/or fractionation. The physical properties of fraction I and II differed in certain aspects. The aggregation response of fraction I to increasing concentrations of monovalent cations was five times lower than that of fraction II but the aggregation response to divalent cations was identical. Thermal denaturation assays of DNAs isolated from fractions I and II revealed identical derivative profiles of hyperchromicity vs temperature, thereby indicating similar base composition in the two fractions. Circular dichroism, spectra of the purified DNAs isolated from both fractions showed identical B-type conformations. However, DNA renaturation kinetics analyzed by computer technique indicated that fraction I DNA contained less than half the amount of highly repetitive sequences as compared to either unfractionated chromatin or fraction II. Circular dichroism spectra of fraction I and II chromatins (at room temperature) showed significant differences in a wavelength region were only DNA is optically active (i.e. 255-320 nm). These results indicated that the DNA complexed to proteins in fraction II assumed a more C-type conformation than the DNA in fraction I. The differences in the circular dichroism spectra could not be accounted for by differences in the RNAs or protein chromophores contained in fraction I and fraction II. When the circular dichroism spectra of fraction I and II were recorded at 55 degrees C, the differences between the two fractions were abolished. These results were interpreted to mean that the differences in the DNA conformations found in fractions I and II were due to the differences in their nonhistone proteins. These proteins were effective in maintaining DNA conformation differences only when they were in their native form but not when heated to 55 degree C. Comparison of the sedimentation coefficients of fractions I and II with their calculated molecular weights suggested a more extended structure in fraction I as compared to a more compact structure in fraction II. Only small differences were observed between fraction I and fraction II with respect to either buoyant density analysis in a metrizamide gradient or in the number of phosphate charges accessible to polylysine.

Studies on the organisation of the chicken genome and its expression during myogenesis in vitro

DNA from the chicken genome was analysed both by isopycnic centrifugation in cesium salt density gradients and by reassociation analysis using hydroxyapatite (HAP) chromatography. Centrifugation in neutral CsCl revealed a single non-Gaussian band skewed toward the heavy side, but no discrete satellite components. In heavy metal (Ag+ or Hg++)-Cs2SO4 gradients, 4-8 satellite bands were revealed, comprising 5-9% of the total DNA. Purification of the satellites and recentrifugation in neutral CsCl demonstrated that 80-90% of this DNA would band in the shoulder, with the remainder in the main band. These satellites can account at most for 30% of the heavy shoulder DNA, thus most of the heavy shoulder DNA must be of lower repetition frequencies. Reassociation analyses of chicken DNA demonstrated that the complexity of the non-repetitive DNA is 9.49 X 10(8) nucleotide pairs, equivalent to about 90% of the haploid genome. Repetitive DNA comprises only 8-10% of the genome and has the following composition, relative to total DNA: 3.7% intermediate repetitive, 1.9% highly repetitive, and 3.9% "zero-time binding" DNA. This unusually low repetitive DNA content may be related to the small genome size of chickens, relative to other vertebrates, and to the presence of many microchromosomes in the chicken karyotype. Total cell RNA extracted from perfusion myoblasts, post-fusion myotubes, and myoblasts grown in BrdU was incubated in large excess with 3H-TdR labelled non-repetitive DNA and the resulting hybrids assayed by HAP chromatography. The amount of non-repetitive DNA represented in the RNA was found to increase from 7-8% in the myoblast stage to 10-11% in myotubes. An even smaller proportion, about 5%, is represented in the RNA of myoblasts prevented from differentiating by growth in BrdU.

Analysis of the complexity and diversity of mRNA from chicken liver and oviduct

We have analyzed the sequence complexity and diversity of poly(A)-containing mRNA derived from two highly differentiated chicken tissues. Two independent approaches were used in our analyses. The first involves the annealing of cDNA copies of mRNA to a vast excess of the template RNA; the second procedure uses hybridization between highly radioactive single-copy genomic DNA and mRNA. The results obtained using these two experimental approaches are in good accord and reveal the presence of 12,000-15,000 diverse mRNA species in both chicken liver and oviduct. In both cell types, the kinetics of annealing of cDNA to its template mRNA demonstrate discrete frequency classes with most of the different mRNA species present in fewer than 10 copies per cell. 70% of oviduct mRNA, however, consists of about 10 abundant RNA species, which probably are responsible for the synthesis of the egg white proteins. The diversity of mRNA species in chicken liver and oviduct was further studied by heterologous annealing reactions between cDNA or singlecopy genomic DNA and a vast excess of mRNA. These studies demonstrate that 85% of the different mRNA sequences detected are present in both liver and oviduct, and suggest that the vast majority of the information expressed as mRNA is required for the maintenance of cellular functions common to all tissues.

Reassociation kinetics of deoxyribonucleic acid in antigen-stimulated mouse-spleen cells

In order to directly compare the complexity of the genome of lymphoid cells which have been antigenically stimulated, with that of non-immunized and non-lymphoid cells, DNA was pulse labeled and extracted from BALB/c mouse spleen cells at various time intervals after antigenic stimulation in vivo; the reassociation rates of these newly synthesized DNA preparations were compared with those of the total mouse spleen DNA, obtained from same sources and at the same times. DNA labeled for 60 min at 43, 53, or 72 h after antigenic restimulation, reassociated faster than the corresponding total DNA. On the other hand, the ressociation profile of DNA, labeled for 60 min during the first 24 after restimulation did not differ from that of the total DNA extracted at the same time. When labeled thymidine was available for incorporation at a constant concentration over a period of 24 h, reassociation patterns of labeled DNA were identical to those of the corresponding total DNA at all times after restimulation. Newly synthesized nuclear DNA exhibited reassociation profiles identical to those of the corresponding total nuclear DNA at all times tested. Also, no differences between the reassociation rates of nuclear and total cellular DNA were observed. It was concluded that antigenic stimualtion does not induce a major amplification of genes in the stimulated cells, and that the rapidly reassociating DNA species described represent extranuclear (cytoplasmic) DNA.

Distribution of 5-bromodeoxyuridine in the DNA of rat embryo cells

Rat embryo cells were treated with (3)H-labeled 5-bromodeoxyuridine (BrdU) in order to determine the nature of substitution and distribution of the analog in DNA. At optimal oncornavirus-inducing doses of BrdU (10(-4) M), density gradient centrifugation and DNA.DNA reassociation experiments revealed extensive (>90%) and uniform base substitution in repetitive, intermediate, and unique DNA sequences. Suboptimal doses (10(-7) M) of [(3)H]BrdU resulted in less than 5% thymine replacement and nonrandom labeling of DNA. Treatment of cells with 10(-7) M [(3)H]dT resulted in relatively uniform labeling throughout all DNA sequences. At low concentrations, BrdU was incorporated predominantly within the repetitive and intermediate DNA of rat embryo cells. Moreover, the single-copy DNA sequences were lightly substituted and reassociated extensively only in the presence of excess unlabeled DNA. Such specificity of base substitution may be related to the unusually selective nature of BrdU effects on animal cells.

Female steroid hormones and target cell nuclei

The data discussed herein demonstrate the great variation in target-tissue response that can occur after administration of steroid hormones. The female sex steroids can exert regulatory effects on the synthesis, activity, and possibly even the degradation of tissue enzymes and structural proteins. Each response, nevertheless, appears to be dependent on the synthesis of nuclear RNA. In many instances, the steroid actually promotes a qualitative change in the base composition and sequence of the RNA synthesized by the target cell, implying a specific effect on gene transcription. Most important is our direct quantitative evidence that sex steroids cause a net increase in the intracellular amounts of specific mRNA molecules in target tissues. It thus appears that we are discovering a pattern of steroid hormone action which includes (Fig. 1): (i) uptake of the hormone by the target cell and binding to a specific cytoplasmic receptor protein; (ii) transport of the steroid-receptor complex to the nucleus; (iii) binding of this "active" complex to specific "acceptor" sites on the genome (chromatin DNA and acidic protein); (iv) activation of the transcriptional apparatus resulting in the appearance of new RNA species which includes specific mRNA's; (v) transport of the hormone-induced RNA to the cytoplasm resulting in synthesis of new proteins on cytoplasmic ribosomes; and (vi) the occurrence of the specific steroid-mediated "functional response" characteristic of that particular target tissue. To elucidate fully the mechanism of steroid hormone action we must study the biochemistry of the process by which information held by the steroid hormone-receptor complex is transferred to the nuclear transcription apparatus. If our assumptions are correct, we should ultimately be able to discover how this hormone-receptor complex exerts a specific regulatory effect on nuclear RNA metabolism. Such regulation might be achieved (i) by direct effects on chromatin template leading to increased gene transcription and thus RNA synthesis; (ii) by activation of the polymerase complex itself; (iii) by inhibition of RNA breakdown; or (iv) by intranuclear processing of large precursor molecules so that smaller biologically active sequences are produced, and (v) by transport of RNA from the nucleus to the cytoplasmic sites of cellular protein synthesis.

Synthesis of (3H)DNA complementary to ovalbumin messenger RNA: evidence for limited copies of the ovalbumin gene in chick oviduct

Accumulation of ovalbumin messenger RNA in chick oviduct is absolutely dependent upon estrogen. After estrogen treatment, ovalbumin comprises 60-65% of the total oviduct protein. We used maximally stimulated animals to extract and partially purify the ovalbumin messenger RNA. The final product was enriched about 100-fold in activity with respect to this specific messenger RNA. This ovalbumin messenger RNA fraction was used to direct the synthesis of a complementary [(3)H]DNA in the presence of RNA-dependent DNA polymerase isolated from avian myeloblastosis virus. The complementary [(3)H]DNA (specific radioactivity, 8 x 10(7) cpm/mug) was a faithful transcript since about 90% would hybridize back to the original messenger RNA template. Ovalbumin complementary [(3)H]DNA was reannealed with an excess of chick-oviduct total DNA. The kinetics of this reaction indicate that only one copy of the ovalbumin gene exists in each haploid genome. These data suggest that estrogen may affect the oviduct genome to stimulate production of large numbers of ovalbumin messenger RNA molecules from a single copy of the ovalbumin gene.