Biomedical subjects

T H Adams

Publications and source records attributed to T H Adams.

At least 55 records · Page 3Linked to original sources

PubMed1992

Isolation of a gene required for programmed initiation of development by Aspergillus nidulans.

In contrast to many other cases in microbial development, Aspergillus nidulans conidiophore production initiates primarily as a programmed part of the life cycle rather than as a response to nutrient deprivation. Mutations in the acoD locus result in "fluffy" colonies that appear to grow faster than the wild type and proliferate as undifferentiated masses of vegetative cells. We show that unlike wild-type strains, acoD deletion mutants are unable to make conidiophores under optimal growth conditions but can be induced to conidiate when growth is nutritionally limited. The requirement for acoD in conidiophore development occurs prior to activation of brlA, a primary regulator of development. The acoD transcript is present both in vegetative hyphae prior to developmental induction and in developing cultures. However, the effects of acoD mutations are detectable only after developmental induction. We propose that acoD activity is primarily controlled at the posttranscriptional level and that it is required to direct developmentally specific changes that bring about growth inhibition and activation of brlA expression to result in conidiophore development.

Aspergillus nidulans↗

PubMed1991

Isolation and transcriptional characterization of a morphological modifier: the Aspergillus nidulans stunted (stuA) gene.

The functions of at least four potential regulatory genes are known to overlap temporally during elaboration of the multicellular asexual reproductive apparatus (conidiophore) of Aspergillus nidulans. One of these, the stuA (stunted) gene, has been previously classified as a morphological modifier essential for correct spatial organization of the conidiophore. The gene was cloned by complementation of a strain carrying the stuA1 mutation and has been localized to a 5.0 kb KpnI fragment that encodes a 3.3 kb mRNA. The stuA mRNA was detected at very low levels in mature conidia and in somatic hyphae that had not established developmental competence. A dramatic increase in the abundance of this mRNA occurred coincidentally with the establishment of competence, but prior to the induction of conidiation. RNA abundance remained at this elevated level during conidiophore morphogenesis. These results are consistent with genetic data suggesting that stuA gene function is required from the very earliest events of asexual reproduction until completion of conidiophore development, but is not specifically required for differentiation of conidia. The expression of the stuA transcript was not affected by any of the other characterized developmental mutations. These latter results suggest that transcriptional activation at the onset of competence is mediated by an as yet unidentified genetic locus or loci.

Aspergillus nidulans↗

PubMed1991

Use of synthetic oligonucleotide DNA probes for identification and direct detection of Bacteroides forsythus in plaque samples.

Oligonucleotide DNA probes complementary to the hypervariable region of the 16S rRNA of Bacteroides forsythus were tested for their specificity and sensitivity against reference and clinical isolates of 73 different species of bacteria. The probes were used to detect the organism directly from nucleic acid extracts of subgingival plaque samples, and the results were compared with results of detection by culture methods. The data demonstrate that the probes are very specific (100%) and sensitive (100% when they are compared with those obtained by the culture method) and could reliably detect the organism in plaque samples. When a probe to a conserved region of the 16S rRNA (UP9A) was used to estimate the quantity of bacteria present in plaque samples, it gave results comparable to those of culture methods. The data suggest that total microbial load may be a parameter in periodontal disease.

Bacteroides↗

PubMed1990

Developmental repression of growth and gene expression in Aspergillus.

Asexual reproductive development can be initiated in Aspergillus nidulans in the presence of excess nutrients through artificial induction of the developmental regulatory genes brlA or abaA by fusing the genes to the promoter from the alcohol dehydrogenase I gene (alcA) and culturing cells in the presence of an inducing alcohol. Artificially induced development completely inhibits growth and represses expression of the endogenous alcA gene and the coordinately controlled aldehyde dehydrogenase gene (aldA). Repression of alcA and aldA expression probably occurs at both the transcriptional and posttranslational levels. We propose that developmental induction results in a generalized metabolic shutdown, leading to an inability of cells to acquire nutrients from the growth medium. Self-imposed nutrient limitation could reinforce the primary developmental stimulus and ensure progression through the asexual reproductive pathway.

Alcohol Dehydrogenase↗

PubMed1990

brlA requires both zinc fingers to induce development.

Expression of the Aspergillus nidulans brlA gene induces a developmental pathway leading to the production of asexual spores. We have introduced mutations into brlA that are expected to disrupt either or both Cys2-His2 Zn(II) coordination sites postulated to exist in the BrlA polypeptide. The resultant brlA alleles fail to induce either the asexual reproductive pathway or the expression of development-specific genes. These data support the hypothesis that brlA encodes a nucleic acid-binding protein whose activity requires each of two zinc fingers.

Alleles↗

PubMed1990

Upstream elements repress premature expression of an Aspergillus developmental regulatory gene.

The Aspergillus nidulans abaA gene regulates intermediate steps in asexual reproductive development and is itself developmentally regulated. An 822-base-pair DNA fragment from the abaA 5'-flanking region is sufficient to drive developmentally appropriate expression of the Escherichia coli lacZ gene. Deletion analysis showed that this fragment contains elements that repress transcription in vegetative cells and immature conidiophores and that activate transcription later during development. A 45-base-pair region encompassing the major and minor abaA transcription initiation sites contains directly repeated sequences related to the mammalian initiator (Inr) element (S. T. Smale and D. Baltimore, Cell 57:103-113, 1989). This element or sequences in the untranslated leader were sufficient for correct transcription initiation and for measurable developmental induction. Similar elements were present at or near the initiation sites of other developmentally regulated genes. We propose that the temporal and spatial specificity of expression of these genes results from modulation of the activity of Inr elements.

Aspergillus niger↗

PubMed1989

Interactions of three sequentially expressed genes control temporal and spatial specificity in Aspergillus development.

Aspergillus nidulans brlA, abaA, and wetA form a dependent pathway that regulates asexual reproductive development. The order in which these genes are expressed determines the outcome of development. Expression of brlA in vegetative cells leads to activation of abaA and wetA, cessation of vegetative growth, cellular vacuolization, and spore formation. By contrast, expression of abaA in vegetative cells does not result in conidial differentiation but does lead to activation of brlA and wetA, cessation of vegetative growth, and accentuated cellular vacuolization. brlA, abaA, and wetA act individually and together to regulate their own expression and that of numerous other sporulation-specific genes. We propose that the central pathway controlling development is largely autoregulatory. The timing and extent of expression of the regulatory genes and their targets are determined as development proceeds by intrinsically controlled changes in the relative concentrations of regulatory gene products in the various conidiophore cell types.

Amino Acid Sequence↗

PubMed1989

A large cluster of highly expressed genes is dispensable for growth and development in Aspergillus nidulans.

We investigated the functions of the highly expressed, sporulation-specific SpoC1 genes of Aspergillus nidulans by deleting the entire 38-kb SpoC1 gene cluster. The resultant mutant strain did not differ from the wild type in (1) growth rate, (2) morphology of specialized reproductive structures formed during completion of the asexual or sexual life cycles, (3) sporulation efficiency, (4) spore viability or (5) spore resistance to environmental stress. Thus, deletion of the SpoC1 gene cluster, representing 0.15% of the A. nidulans genome, had no readily detectable phenotypic effects. Implications of this result are discussed in the context of major alterations in gene expression that occur during A. nidulans development.

Aspergillus nidulans↗

PubMed1988

brlA is necessary and sufficient to direct conidiophore development in Aspergillus nidulans.

The brlA gene of A. nidulans mediates the developmental switch from the indeterminate, apical growth pattern of vegetative cells to the budding growth pattern of conidiophores. brlA encodes a 432 amino acid polypeptide containing two directly repeated motifs resembling the Zn(II) coordination sites first recognized in Xenopus TFIIIA. Misscheduled expression of brlA in vegetative cells results in transcriptional activation of developmentally regulated genes, cessation of unidirectional hyphal growth, initiation of cellular transformations resembling those that occur during normal conidiophore development, and production of viable conidiospores. We propose that BRLA is a nucleic acid-binding protein whose expression in vegetative cells is sufficient to induce sporulation through its role in regulating expression of conidiation-specific genes.

Amino Acid Sequence↗

PubMed1984

Physical organization of the Bradyrhizobium japonicum nitrogenase gene region.

In Bradyrhizobium japonicum USDA 110 the three genes that encode the nitrogenase enzyme complex are separated into two transcription units, nifH and nifDK. We have physically mapped a 33-kilobase-pair region of the B. japonicum genome that contains both nifH and nifDK. The nifDK operon is located transcriptionally upstream from nifH, and all three genes are transcribed in the same direction. Within the 20-kilobase-pair region that separates the promoters for these two transcription units, we have identified a region homologous to the Klebsiella pneumoniae nifA gene. This nifA homology is situated about 6 kilobase pairs upstream from the nifH transcriptional initiation signal, in an analogous position to the nifA-like locus previously described for Rhizobium meliloti. In addition, we have characterized a second distinct nifA homology in B. japonicum that is not directly linked to the nitrogenase structural gene region.

Base Sequence↗

PubMed1984

The nifH and nifDK promoter regions from Rhizobium japonicum share structural homologies with each other and with nitrogen-regulated promoters from other organisms.

In several species of Rhizobium the three genes which encode the nitrogenase complex are separated into two operons, nifH and nifDK. We have mapped the transcriptional promoter sites for these two operons from R. japonicum USDA strain 110 by S1 protection analyses using bacterial RNA isolated from soybean nodules. Transcription of the nifDK operon is initiated at a site located 46 nucleotides upstream of the proposed translation initiation codon. nifH transcription initiates predominantly at a site 152 nucleotides upstream of the proposed translation initiation codon. An additional minor start for nifH is found 35 nucleotides downstream of the major initiation site. The nucleotide sequences of these promoter sites are presented. Comparison of the major R. japonicum nif promoter sequences reveals a high degree of sequence homology with the conserved sequences clustered in the -11 to -15, -21 to -25, -27 to -31, and -38 to -41 regions. Conservation is also observed for the -11 to -15 and -21 to -25 regions with the R. meliloti nifHDK, a cowpea Rhizobium nifH, and even Klebsiella pneumoniae nif promoters. The -27 to -31 and -38 to -42 region homologies are not conserved with the other known nif promoters. These results are discussed in light of models for nif promoter activation.

Base Sequence↗

PubMed1983

Stability, characterization, and kinetics of 111In-labeled monoclonal antitumor antibodies in normal animals and nude mouse-human tumor models.

Monoclonal antibodies (MoAbs) against carcinoembryonic antigen were successfully radiolabeled with 111In, and the radiopharmaceutical was characterized in vitro and in normal and tumor-bearing mice. The 111In-MoAb proved to be stable in vitro and in vivo under normal conditions, although instability could be induced in vitro with large quantities of iron-free transferrin. Animal distribution studies with 111In-MoAb demonstrated tumor localization superior to 67Ga and pharmacokinetics that were highly similar to those of endogenously labeled 75Se-MoAb. The 111In-MoAb followed first-order kinetics and fit a two-compartmental model when studied in nude mice bearing human colon tumors known to express carcinoembryonic antigen. Significant quantities of radiolabel appeared in tissues other than tumor, with liver and skin having the highest concentrations. Sufficient tumor/background ratios were formed for scanning purposes. The data indicate that 111In-MoAb may prove to be effective as a radiopharmaceutical for tumor imaging.

Animals↗

PubMed1981

The hybridoma-an immunochemical laser.

The advent of hybridoma technology has provided the immunotechnologist a finely tunable instrument that should permit a marked advance in the immunologic sciences. The ability to choose the precise antibody required and the virtually unlimited availability of easily purified antibodies have already resulted in the simultaneous immunometric assay and potential reagents for immunoscintigraphy and immunotherapy. Using an antibody with a specific affinity and recognition for a specific antigenc determinant can greatly influence the shape and range of a radioimmunometric calibration curve. With monoclonal antibodies, assay systems based on immune complexes (e.g., turbidimetric assays and counterimmunoelectrophoresis) can be made more precise, thus permitting study of the basic physicochemical principles underlying the antigen-antibody reaction and the development of greatly improved quantitative assays. On the other hand, the ability to select an antibody exhibiting specific characteristics implies the necessity to select. One no longer has the luxury of using a mixture of antibodies, hoping to take advantage of the fact that some will have desirable secondary characteristics such as electrophoretic mobility or the ability to absorb to plastics.

Animals↗

PubMed1980