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Biomedical subjects

A R Means

Publications and source records attributed to A R Means.

At least 271 records · Page 15Linked to original sources
PubMed1975

Androgen binding protein as a biochemical marker of formation of the blood-testis barrier.

Androgen binding protein (ABP) was measured during postnatal development in normal and irradiated rats to determine whether development of a blood-testis barrier and formation of a continuous lumen from testis to epididymis is correlated with entry of ABP into the caput epididymis. ABP is found in normal testis as early as 14 days postnatally (0.2 pmol/mg), at which time no blood-testis barrier is observed by the peroxidase perfusion technique. Previous findings have shown a close correlation of blood-testis barrier development and lumen formation. Indeed, ABP is not detectable in the epididymis until 18-20 days of age (1.0 pmol/mg) at which time blood-testis barrier formation and lumen development is complete. Whole body irradiation (125 rads) of pregnant rats at 19-20 days of gestation produces male offspring with seminiferous tubules remarkably free of germinal epithelium and containing essentially only Sertoli cells. These Sertoli cell-enriched (SCE) testes produce normal amounts of ABP between 14 and 21 days postnatally. However, between 21 and 30 days of age the specific activity of ABP is significantly higher in the SCE tests (2.8 pmol/mg protein) than in normal testis (0.5 pmol/mg protein). In the SCE testis neither blood-testis barrier development nor lumen formation are complete until 30 days of age, at which time ABP is first detectable in epididymis of the irradiated rat. Thereafter there is a gradual decline of ABP in the SCE testis-and a dramatic increase in the epididymis. NIH-FSH-S-10 (200 mug/rat) injected SC into 14-day-old normal rats stimulated ABP in the testis from control levels of 0.15 pmol/mg to 1.46 pmol/mg within 4 h after injection. However, no ABP was detectable in the epididymis of either the control or the FSH-stimulated rats. These findings suggest that entry of ABP into caput epididymis is an index of blood-testis barrier formation and lumen development.

Androgens↗
PubMed1974

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.

Animals↗
PubMed1973

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.

Animals↗
PubMed1973

Rates of induction of specific translatable messenger RNAs for ovalbumin and avidin by steroid hormones.

In the chick oviduct, injections of estrogen and progesterone induce synthesis of the specific proteins ovalbumin and avidin, respectively. We have studied the rate of induction of the specific messenger RNA molecules for these proteins after a single injection of estrogen or progesterone. The mRNAs were extracted, partially purified, and quantified in vitro in a heterologous protein-synthesizing system. Single injections of estrogen in chicks previously withdrawn from all steroid hormones for 2 weeks led to rapid increases in ovalbumin mRNA with 3 hr, which coincided with increases in the rate of ovalbumin synthesis. Maximal ovalbumin mRNA activity occurred by 18-20 hr. The half-life of the mRNA was estimated to be 8-10 hr and corresponded to the half-life for cessation of intracellular ovalbumin synthesis after a single injection of an estrogen. Similarly, after an injection of progesterone into chicks first treated with estrogen, appearance of avidin mRNA preceded demonstrable accumulation of this specific protein in oviduct cells. The mRNA for avidin was first apparent at 6 hr, and reached maximal concentrations between 18 and 24 hr after injection. These data confirm that both estrogen and progesterone act on oviduct to induce rapid accumulation of specific mRNAs before and coincident with the appearance of the cell-specific induced proteins. The overall results of these experiments are compatible with the hypothesis that the production of mRNA is a rate-limiting step in the steroid hormone-mediated induction of protein synthesis.

Animals↗
PubMed1972

Ovalbumin messenger RNA of chick oviduct: partial characterization, estrogen dependence, and translation in vitro.

A rapidly-labeled RNA fraction can be isolated from hen oviduct polysomes that has characteristics of the messenger RNA (mRNA) for the cell-specific protein, ovalbumin. This RNA, which sediments in the 8-17S region of sucrose gradients, possesses properties suggestive of the presence of a polyadenylic acid sequence and can be translated with fidelity in a cell-free protein synthesizing system derived from rabbit reticulocytes. The identity of the protein product as ovalbumin is confirmed by three methods, and translation of ovalbumin mRNA is shown to be dependent both on amount of exogenous mRNA and incubation time. Both rate and extent of ovalbumin synthesis is enhanced by the addition of a protein extract from ribosomes that contains peptide chain initiation factors. Finally, the presence of this specific mRNA is shown to be estrogen-dependent: it is induced by estrogen administration to immature chicks, disappears upon cessation of estrogen treatment, and can be reinduced by a single injection of estrogen to chicks that have been pretreated with estrogen and then withdrawn from the hormone.

Acrylamides↗