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Biomedical subjects

J D Wilson

Publications and source records attributed to J D Wilson.

At least 163 records · Page 9Linked to original sources
PubMed1991

Aromatase mRNA in the extragonadal tissues of chickens with the henny-feathering trait is derived from a distinctive promoter structure that contains a segment of a retroviral long terminal repeat. Functional organization of the Sebright, Leghorn, and Campine aromatase genes.

The henny-feathering trait is an autosomal dominant mutation that causes the expression of aromatase activity and accumulation of aromatase mRNA in extragonadal tissues of chickens. The current studies establish that the aromatase gene is not amplified and is organized similarly in control (Leghorn) and henny-feathered (Sebright and Campine) birds. Nucleotide sequence analysis of the nine coding exons of the aromatase gene reveals that the predicted amino acid sequence is identical in all three strains. We, therefore, characterized the genomic DNA segments flanking the coding segment of the Sebright, Leghorn, and Campine aromatase genes. The site of transcription initiation utilized in the ovary of all three strains is located approximately 147 nucleotides upstream of the initiator methionine. In addition to aromatase mRNA derived from this common ovarian promoter, another species of aromatase mRNA is present in Sebright and Campine ovary and is the only type detected in Sebright fibroblasts. cDNA copies of this second species of aromatase mRNA contain a unique 5' terminus, suggesting that a second promoter controls extragonadal aromatase expression in birds that carry the henny-feathering trait. Nucleotide sequence analysis of this 5' terminus indicates that this segment is derived from a retroviral long terminal repeat.

Amino Acid Sequence↗
PubMed1991

Feed-forward control of prostate growth: dihydrotestosterone induces expression of its own biosynthetic enzyme, steroid 5 alpha-reductase.

Dihydrotestosterone, the primary mediator of prostate growth, is synthesized in target tissues from the circulating androgen testosterone through the action of steroid 5 alpha-reductase (EC 1.3.99.5). The expression of 5 alpha-reductase and the level of 5 alpha-reductase messenger RNA in rat ventral prostate are regulated by androgens. To determine whether this control is mediated by dihydrotestosterone or testosterone, we investigated the effect of finasteride, a potent inhibitor of steroid 5 alpha-reductase, on the expression of 5 alpha-reductase in the prostate. The administration of finasteride to intact rats for 7 days caused a 55% decrease in prostate weight and an 87% decrease in 5 alpha-reductase enzyme activity. Furthermore, the restoration of prostate growth after castration and the enhancement in 5 alpha-reductase enzyme activity and 5 alpha-reductase messenger RNA level by testosterone administration were blocked by finasteride, whereas the inhibitor had no effect on dihydrotestosterone-mediated increases in 5 alpha-reductase activity or messenger RNA level. These findings indicate that dihydrotestosterone itself controls prostate growth and 5 alpha-reductase activity. They further suggest that prostate growth is controlled by a feed-forward mechanism by which formation of trace amounts of dihydrotestosterone induces 5 alpha-reductase, thereby increasing dihydrotestosterone synthesis and triggering a positive developmental cascade.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1991

Multifunctional features of a gastrodermal sensory cell in Hydra: three-dimensional study.

Computer-assisted, three-dimensional reconstructions of two gastrodermal sensory cells from transmission electron micrographs of serial sections of Hydra revealed a unipolar morphology with the nucleus near an apical cilium and a simple unbranched axon with a widened terminal. The sensory cells were similar in size and shape to a unipolar sensory cell isolated from macerated gastrodermis and examined with scanning electron microscopy. In thin sections, the cells were characterized by the presence of numerous dense-cored vesicles in the axon and its terminal. A few dense-cored vesicles were aligned at electron-dense synaptic foci in the axon terminal of the sensory cell, which formed an axo-axonal synapse with a nearby centrally located ganglion cell and a neuromuscular synapse with the basal myoneme of a digestive cell. The ganglion cell possessed a perikaryal cilium and a slender axon that extended adjacent to the sensory cell terminal, where it formed an en passant axo-axonal synapse in reciprocal arrangement with that of the sensory cell. In addition, the ganglion cell axon formed a neuromuscular synapse in sequence with the sensory cell axo-axonal synapse. The presence of a large number of neurosecretory-like granules, apical cilium and reciprocal interneuronal and neuromuscular synaptic loci suggests that this gastrodermal sensory cell, characterized ultrastructurally for the first time, represents a third type of multifunctional neuron in Hydra. Thus, Hydra may contain primitive stem-like neurons, which are sensory-motor and also function in both neurosecretion and neurotransmission.

Animals↗
PubMed1991

Effect of radiation combined with hyperthermia on human prostatic carcinoma cell lines in culture.

The effect of radiation combined with heat on three human prostatic carcinoma cell lines growing in vitro was investigated. Cells were exposed to different radiation doses followed by heat treatment at 43 degrees C for one hour. Heat treatment, given ten minutes after radiation, significantly enhanced the radiation response of all the cell lines studied. The combined effect of radiation and heat produced greater cytotoxicity than predicted from the additive effects of the two individual treatment modalities alone. These results indicate that a combined treatment regimen of radiation plus hyperthermia (43 degrees, 1 hr) might be an important tool in maintaining a better local control of prostatic cancer.

Cell Survival↗
PubMed1991

Androgen increases androgen receptor protein while decreasing receptor mRNA in LNCaP cells.

We have examined the effect of androgen treatment on androgen receptor mRNA and protein expression in the LNCaP human prostate carcinoma cell line. Incubation with androgen caused a decrease in cellular androgen receptor mRNA content that was concentration and time dependent. Maximal suppression to approximately 35% of control level was observed after 49 h of exposure to androgen. By contrast, incubation of LNCaP cells with androgen resulted in a 2-fold increase in the cellular content of androgen receptor protein at 24 h. At 49 h androgen receptor protein increased 30% as assayed by immunoblots and 79% as assayed by ligand binding. These results suggest that ligand-induced changes in androgen receptor stability and/or the translational efficiency of androgen receptor mRNA account for the phenomenon of androgen receptor upregulation observed in cultured LNCaP cells. Furthermore, the suppression of androgen mRNA and protein that is caused by prolonged incubation with androgen is incomplete and is reversible upon removal of ligand.

Androgens↗
PubMed1991

The effect of radiation therapy and hyperthermia on a human prostatic carcinoma cell line grown in athymic nude mice.

The effect of radiation and/or hyperthermia on a human prostatic carcinoma xenograft in athymic nude mice was investigated. A human prostate carcinoma subline (1-LN-PC-3-1A) was inoculated subcutaneously in the thigh of male athymic nude mice. When tumors reached a size of approximately 200 mm.3, they were treated with either radiation (X) or hyperthermia (H) alone, or in combination (X + H). In the combined treatment, hyperthermia was delivered immediately after radiation exposure. Comparison of the time required to reach twice the tumor volume observed at the time of treatment was used to define therapeutic impact on tumor growth. The combined treatment resulted in median tumor volume doubling time of 35.5 days, compared to 18 days and 25.5 days, respectively, for hyperthermia or radiation alone. Analysis of tumor doubling time using a proportional hazards regression indicates that under the conditions of this experiment, the effect of radiation and hyperthermia for 1-LN-PC-3-1A tumors is additive. The impact of this treatment regimen in the management of prostatic cancer requires further investigation.

Animals↗
PubMed1991

Androgen resistance caused by mutations in the androgen receptor gene.

Defects in the human androgen receptor cause a spectrum of defects in male phenotypic sexual development associated with abnormalities in the receptor protein assayed in cultured fibroblasts and in broken cell assays. In some patients these abnormalities are associated with absent ligand binding, in other qualitative or quantitative abnormalities of ligand binding are present, and in some no abnormality of ligand binding is detected. Analysis of the androgen gene structure in such patients has permitted identification of the causative mutation in many families. Although results of these studies often reinforce concepts established by in vitro mutagenesis studies of other steroid receptors, some mutations have provided unusual insight into the structural organization of the androgen receptor molecule.

Androgens↗
PubMed1991

A cluster of male pseudohermaphrodites with 5 alpha-reductase deficiency in Papua New Guinea.

We report a cluster of male pseudohermaphrodites from the Simbari Anga linguistic group in the Eastern Highlands of Papua New Guinea. These subjects are born with a rudimentary clitoral-like penis and pseudovaginal perineoscrotal hypospadias. At puberty, the penis enlarges with concurrent growth of pubic and axillary hair and significant muscular development. There is significant facial hair, but it is less than that of their normal male siblings or other male relatives. Plasma collected from four adult subjects revealed elevated plasma testosterone levels, low to low normal dihydrotestosterone levels, and elevated testosterone/dihydrotestosterone ratios. All subjects had high urinary aetiocholanolone/androsterone ratios, and C19 and C21 5 beta/5 alpha metabolite ratios. Decreased 5 alpha-reductase activity was demonstrated in fibroblasts cultured from genital skin. The data indicate a phenotypic and biochemical profile similar to patients studied in the Dominican Republic, except for a greater abundance of facial and body hair. The phenotypic variability, as pertains to facial and body hair, may be related to differences in familial expression, as well as the degree of enzyme deficiency. Infants, thought to be females at birth, were reared as girls until puberty in a society practising one of the strictest gender segregations known. At puberty, these 'girls' were discovered to be boys, and a switch of gender roles was instituted. Recently, however, some Muniri, Dunkwi and northern Simbari hamlets recognize these individuals as male in infancy and rear them as boys, calling them 'kwalatmala' to distinguish them from normal males, accepting them as an intersex destined to occupy male adult roles.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1991

A study of the shape of dose-response curves for acute lethality at low response: a "megadaphnia study".

Dose-response curves were developed for the immobilization response in Daphnia magna to four toxicants. The purpose of this work was to study the effect of the form of the model and the number of concentration levels used on the estimates of typical low-dose effective concentrations (1%, 5%, 10%). The generalized four-parameter logistic model was used as the reference. When using 12 concentration levels, one of the logistic family two- or three-parameter models was shown reliably to represent each of these various sets of dose-response data, and to provide adequate estimates of EC01 and EC05, as well as EC10 and EC50. For two of the toxicants, an asymmetric model was required. When reducing the number of concentrations to five, the EC10 and EC50 were well estimated by the probit model, with acceptable results at the EC05 level.

Animals↗
PubMed1991

A mutation in the DNA-binding domain of the androgen receptor gene causes complete testicular feminization in a patient with receptor-positive androgen resistance.

Androgen resistance is associated with a wide range of quantitative and qualitative defects in the androgen receptor. However, fibroblast cultures from approximately 10% of patients with the clinical, endocrine, and genetic features characteristic of androgen resistance express normal quantities of apparently normal androgen receptor in cultured genital skin fibroblasts (receptor-positive androgen resistance). We have analyzed the androgen receptor gene of one patient (P321) with receptor-positive, complete testicular feminization and detected a single nucleotide substitution at nucleotide 2006 (G----C) within the second "zinc finger" of the DNA-binding domain that results in the conversion of the arginine residue at position 615 into a proline residue. Introduction of this mutation into the androgen receptor cDNA and transfection of the expression plasmid into eukaryotic cells lead to the synthesis of a receptor protein that displays normal binding kinetics but is inactive in functional assays of receptor activity. We conclude that substitution mutations in the DNA-binding domain of the androgen receptor are one cause of "receptor-positive" androgen resistance.

Androgen-Insensitivity Syndrome↗
PubMed1991

Molecular basis of androgen resistance in a family with a qualitative abnormality of the androgen receptor and responsive to high-dose androgen therapy.

We have examined the nature of the mutant androgen receptor in a family with a severe defect in virilization associated with a qualitative defect in receptor function. The androgen receptor gene in this family contains two structural alterations: a single nucleotide substitution at position 2444 in exon 5 (adenosine----guanosine) that converts tyrosine 761 to a cysteine residue and a shortened glutamine homopolymeric segment in exon 1 that encodes 12 rather than the usual 20-22 glutamines. A family study was performed using polymerase chain reaction amplification of the glutamine-rich segment, and it was shown that the sister of the proband does not carry the mutant allele. The effects of these two mutations on the function of the androgen receptor were studied by introducing the changes, individually and in combination, into cDNAs encoding the normal human androgen receptor and analyzing the receptor protein produced after transfection of the cDNAs into eukaryotic cells. The presence of a cysteine residue at position 761 causes rapid dissociation of dihydrotestosterone from the receptor protein. Marked thermolability of the transfected receptor protein, however, was demonstrable only upon introduction of an androgen receptor cDNA containing both the partial deletion of the glutamine homopolymeric segment and a cysteine residue at position 761. Likewise, the ability of the receptor to stimulate a reporter gene is strikingly diminished only when both alterations are present, suggesting that the shortened glutamine homopolymeric segment amplifies the impairment of receptor function caused by the tyrosine to cysteine substitution.

Base Sequence↗
PubMed1991

Androgen receptor expression in the developing rat prostate is not altered by castration, flutamide, or suppression of the adrenal axis.

Mesenchymal epithelial interactions are believed to be important to the growth and development of the neonatal prostate. Prior studies in the rat ventral prostate, using autoradiography and tritiated dihydrotestosterone, indicate that androgen receptors are present in the prostatic stroma on day 3 and are detected in the epithelium by the tenth postnatal day. These findings suggested that androgen stimulation of the prostatic mesenchyme is a crucial step in the growth and development of the prostate. We have examined this developmental program directly using polyclonal antibodies that recognize specific epitopes of the androgen receptor to examine the pattern of androgen receptor expression in intact and neonatally castrate animals. In keeping with previous studies, androgen receptors are present in the prostate stroma at birth and subsequently appear in the prostatic epithelium by the 10th postnatal day. Development of androgen receptor expression in the epithelium was not changed when the animals were castrated at birth, castrated and blocked by flutamide, or castrated and given hydrocortisone to suppress the production of adrenal androgens. These findings suggest that the appearance of androgen receptors in the prostatic epithelium is programmed by androgens before birth or that factors other than testicular or adrenal androgens control the development of epithelial androgen receptors.

Adrenal Glands↗
PubMed1991

Androgen receptor levels in the rat penis are controlled differently in distinctive cell types.

The rat phallus grows during sexual maturation as serum androgen concentrations rise to adult levels, and growth ceases when sexual maturity is attained despite the continued presence of adult serum androgen levels. This cessation of growth is correlated temporally with a diminution in the levels of androgen receptor, as detected by assays of ligand binding. To determine whether the change in androgen receptor content occurs in all cells in the tissue, immunohistochemical studies of the penile androgen receptor were performed in rats of different ages. In immature animals and animals castrated prepubertally, the androgen receptor is detected in virtually all cell types, including the corpus cavernosum penis, the small lateral cavernous bodies, the corpus cavernosum urethra, skin, urethra, and os penis. By contrast, in the mature rat penis minimal androgen receptor is evident within the corporal tissue and os, although immunoreactivity remains detectable in the penile skin and urethra. It is concluded that the cessation of androgen-mediated growth correlates with a decrease in androgen receptor levels in the body of the penis.

Aging↗
PubMed1991

Decreased levels of the androgen receptor in the mature rat phallus are associated with decreased levels of androgen receptor messenger ribonucleic acid.

Growth of the penis at sexual maturation is under the control of androgens, but growth ceases as the organ reaches adult size despite continued high levels of circulating androgen. Previous studies have shown that the cessation of penile growth is associated with a decrease in the quantity of androgen receptor, as detected by ligand binding and immunological methods. In the current studies we demonstrate that the decreased androgen receptor levels correlate with a decrease in androgen receptor mRNA content in the penile corpus and os, but not in the glans penis. These findings suggest that modulation of androgen receptor mRNA levels in the body of the penis may be important to the control of androgen-dependent growth in the tissue, and that the control of androgen receptor mRNA levels differs among the different cell types that comprise the penis. To explore the mechanisms controlling androgen receptor expression, we examined the transcription initiation site of the rat androgen receptor gene in ventral prostate and in three compartments of the penis: the corpus, the urethra, and the glans penis. The same promoter is employed in all preparations, suggesting that the different patterns of androgen receptor mRNA expression in these tissues with age are controlled by factors that modulate the activity of the same promoter.

Aging↗
PubMed1991

Androgen resistance associated with a mutation of the androgen receptor at amino acid 772 (Arg----Cys) results from a combination of decreased messenger ribonucleic acid levels and impairment of receptor function.

Analysis of the nucleotide sequence of the coding segment of the androgen receptor gene in a patient (N105) with the receptor-negative form of complete testicular feminization has revealed a single substitution (CGC----TGC) at nucleotide 2476. This alteration results in the conversion of an arginine at amino acid 772 to a cysteine. Introduction of this mutation into an androgen receptor cDNA and transfection of the mutant cDNA into COS cells result in the production of a receptor protein with an alteration in the apparent Kd of ligand binding (3 nM) compared to that of the normal androgen receptor (0.5 nM). The mutant receptor protein predicted for patient N105 also demonstrates thermal instability of ligand binding that is not associated with quantitative or qualitative changes in the immunoreactive androgen receptor protein. When assayed in cotransfection experiments using a mouse mammary tumor virus-chloramphenicol acetyl transferase reporter system, the N105 receptor protein appears to be about a tenth as active as the control receptor. These functional characteristics do not appear sufficient to account for the phenotype of complete testicular feminization and do not explain the profound deficiency of androgen receptor in cultured skin fibroblasts. Quantitative S1 nuclease protection assays reveal that the level of androgen receptor mRNA in fibroblasts from patient N105 is markedly reduced. These results suggest that the phenotype in patient N105 is due to two effects of the nucleotide substitution at residue 2476: the replacement of a crucial amino acid (772) in the hormone-binding domain that impairs the function of any receptor molecules formed and a decrease in the level of androgen receptor mRNA.

Androgen-Insensitivity Syndrome↗
PubMed1991

Biological bases for cancer dose-response extrapolation procedures.

The Moolgavkar-Knudson theory of carcinogenesis of 1981 incorporates the viable portions of earlier multistage theories and provides the basis for both the linearized multistage and biologically based dose-response extrapolation methodologies. This theory begins with the premise that cancer occurs because irreversible genetic changes (mutations) are required for transformation of normal cells to cancer cells; incidence data are consistent with only two critical changes being required, but a small contribution from three or higher mutation pathways cannot be ruled out. Events or agents that increase the rate of cell division also increase the probability that one of these critical mutations will occur by reducing the time available for repair of DNA lesions before mitosis. The DNA lesions can occur from background causes or from treatment with mutagenic agents. Thus, the equations describing incidence as a function of exposure to carcinogenic agents include two separate terms, one accounting for mutagenic and one for mitogenic stimuli. At high exposures these interact, producing synergism and high incidence rates, but at low exposures they are effectively independent. The multistage models that are now used include only terms corresponding to the mutagenic stimuli and thus fail to adequately describe incidence at high dose rates. Biologically based models attempt to include mitogenic effects, as well; they are usually limited by data availability.

Dose-Response Relationship, Drug↗