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T L Brown

Publications and source records attributed to T L Brown.

At least 19 recordsLinked to original sources
PubMed1995

Local synthesis of apolipoprotein J in the eye.

Apolipoprotein J (apoJ), a secretory glycoprotein known to transport lipids and to regulate terminal complement function, is present in the human eye in both aqueous and vitreous, as well as in the retina. Ocular apoJ is the product of local synthesis, rather than plasma contamination, as demonstrated by its distinct structural properties and the presence of abundant apoJ mRNA in retina and retina pigment epithelium. ApoJ mRNA is also present in mouse eye, with a developmentally regulated pattern of expression. In fetal mouse, apoJ mRNA is present in retina, lens and cornea. In contrast, adult eye apoJ mRNA is present in retina and ciliary body. We propose that apoJ is important in tissue remodeling and in stabilizing hydrophobic molecules which are required for vision and/or which would otherwise be deleterious and membrane-active.

Aged↗
PubMed1995

Automaticity and word perception: evidence from Stroop and Stroop dilution effects.

The Stroop effect is cut in half by adding a neutral word to the display. D. Kahneman and D. Chajczyk's (1983) "attention capture" account of "Stroop dilution" holds word recognition to be involuntary but strictly serial. The authors compared attention capture to 3 alternatives involving parallel rather than serial processing: In the lexicon, activation is divided among multiple words; postlexically, multiple words race for access to response processes; or prelexically, feature processing is degraded by multiple patterns whether or not they are words. Results support the latter. Multiple patterns are processed in parallel. If any are color words, Stroop effects occur but are reduced because any color word's input to lexical memory is lower in quality than if a single color word were the only pattern. Thus, lexical encoding is involuntary but can operate on several input representations in parallel, with effectiveness determined by input quality.

Adult↗
PubMed1995

Expression of apolipoprotein J in the uterus is associated with tissue remodeling.

The endometrium is a dynamic tissue that, in response to hormonal cues, undergoes cycles of growth and involution. Extracellular factors required for this remodeling are poorly understood. The potential role in endometrial turnover of apolipoprotein J (apoJ), a secretory glycoprotein that can bind lipids and membrane-active proteins, is proposed on the basis of its spatial and temporal patterns of expression during normal cycling, after ovariectomy, and in response to hormone manipulation. In the mouse, apoJ mRNA was expressed in uterine luminal and glandular epithelial cells coincident with the presence of apoJ protein. The apoJ gene was differentially expressed in the glandular and uterine luminal epithelial cells during the estrous cycle and following hormone depletion. Expression of apoJ was not induced in ovariectomized mice by estrogen, progesterone, or dexamethasone treatment alone. Progesterone administration after an initial estrogen pretreatment, however, resulted in dramatic induction of apoJ as the progesterone level declined. In contrast, apoJ was not induced when a long-lived progesterone analog, medroxyprogesterone, was substituted for progesterone. In the human menstrual cycle, apoJ was present in glandular lumens only during the late secretory phase. Declining progesterone levels, causing substantial tissue reorganization, are characteristic of the times of marked apoJ induction in uterine epithelial cells. These expression patterns are consistent with apoJ functioning as an extracellular cytoprotectant by mediating clearance of and/or neutralizing cytolytic tissue debris.

Animals↗
PubMed1992

Structural requirements for RNA editing in hepatitis delta virus: evidence for a uridine-to-cytidine editing mechanism.

Hepatitis delta virus (HDV) nucleotide 1012 is edited from uridine to cytidine in 10-40% of the RNA genomes during replication. This editing event is an important control point in the HDV life cycle because it results in both the packaging of viral RNA and the inhibition of HDV replication. We find that the editing event is highly specific for both the sequences neighboring nucleotide 1012 and the base-paired context of position 1012 within the unbranched rod structure of HDV RNA. Prior studies identified the base transition at nucleotide 1012 but were unable to distinguish between editing of the genomic versus the antigenomic strands [Luo, G. X., Chao, M., Hsieh, S. Y., Sureau, C., Nishikura, K. & Taylor, J. (1990) J. Virol. 64, 1021-1027]. In this study, comparisons of mutations that differentiate between base pairing in genomic and antigenomic RNAs indicate that the genomic strand of HDV is the actual editing substrate. We conclude that the virus uses a uridine to cytidine editing mechanism, which is provided by the host cell.

Animals↗
PubMed1991

Ontogeny of epidermal growth factor receptor tyrosine kinase in rat liver.

The binding of epidermal growth factor (EGF) to its receptor and the activity of the receptor intrinsic protein-tyrosine kinase were studied during the ontogeny of rat liver. The number of EGF receptors during pre- and postnatal development was first compared in crude liver plasma membranes using 1) specific binding of 125I-labeled EGF and 2) immunoblot analysis using any antireceptor polyclonal rabbit antibody. Both methods detected the expression of the EGF receptor in fetal rat liver on day 17 of gestation, but in an amount markedly less than the adult. Within 24 h, there was a more than twofold increase in EGF binding to plasma membranes as well as a marked increase in receptor immunoreactivity. However, after birth, there was a precipitous drop in receptor number to less than 20% of the adult level by the end of the first postnatal day (P less than 0.001). Next, the presence of EGF-stimulated tyrosine kinase activity (autophosphorylation) was determined during the same stages of development. Electrophoresis of membranes phosphorylated in the presence or absence of EGF followed by autoradiography demonstrated autokinase activity stimulated by EGF in day 18 and 19 fetal liver plasma membranes, but not in membranes on day 17 of gestation. Similar to the pattern observed with EGF binding, there was a decrease in autokinase activity in early neonatal plasma membranes followed by an increase to near adult levels by 7 days postnatally. Quantitation of the amount of 32P radioactivity associated with the EGF receptor bands in each age group, correlated with the degree of autophosphorylation assessed by autoradiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

Natural history of experimental woodchuck hepatitis virus infection: molecular virologic features of the pancreas, kidney, ovary, and testis.

The kinetic patterns of woodchuck hepatitis virus (WHV) infection were monitored in the pancreas, kidneys, ovaries, and testes. Groups of woodchucks experimentally infected with a standardized inoculum of WHV were sacrificed at different times over a 65-week period beginning in the preacute phase of viral infection and continuing to the period of serologic recovery or the establishment of chronic infections and subsequent hepatocellular carcinoma (B. E. Korba, P. J. Cote, F. V. Wells, B. Baldwin, H. Popper, R. H. Purcell, B. C. Tennant, and J. L. Gerin, J. Virol. 63:1360-1370, 1989). Tissues from an additional group of long-term (2 to 3 years) chronic WHV carriers which had been infected with the same WHV inocula were also examined. Viral DNA replication intermediates were found in all four tissues during the acute phase of WHV infection. However, WHV DNA replication intermediates were observed only in the kidneys of a small proportion of the chronically infected animals. Following the acute phase of infection, WHV DNA was present only in the pancreas, kidneys, and ovaries of the chronically infected woodchucks. A progressive evolution of different WHV genomic forms related to the replicative state of WHV was observed in these tissues. Histologic evaluation of these four tissues revealed only minimal, localized lesions which were not correlated with the state of WHV activity. The observations compiled in this study further extend the tissue tropism of WHV.

Animals↗
PubMed1990

Interaction of attentional and motor control processes in handwriting.

The interaction between attentional capacity, motor control processes, and strategic adaptations to changing task demands was investigated in handwriting, a continuous (rather than discrete) skilled performance. Twenty-four subjects completed 12 two-minute handwriting samples under instructions stressing speeded handwriting, normal handwriting, or highly legible handwriting. For half of the writing samples, a concurrent auditory monitoring task was imposed. Subjects copied either familiar (English) or unfamiliar (Latin) passages. Writing speed, legibility ratings, errors in writing and in the secondary auditory task, and a derived measure of the average number of characters held in short-term memory during each sample ("planning unit size") were the dependent variables. The results indicated that the ability to adapt to instructions stressing speed or legibility was substantially constrained by the concurrent listening task and by text familiarity. Interactions between instructions, task concurrence, and text familiarity in the legibility ratings, combined with further analyses of planning unit size, indicated that information throughput from temporary storage mechanisms to motor processes mediated the loss of flexibility effect. Overall, the results suggest that strategic adaptations of a skilled performance to changing task circumstances are sensitive to concurrent attentional demands and that departures from "normal" or "modal" performance require attention.

Attention↗
PubMed1989

Hepatitis delta virus (HDV) and woodchuck hepatitis virus (WHV) nucleic acids in tissues of HDV-infected chronic WHV carrier woodchucks.

The molecular forms of genomic and antigenomic hepatitis delta virus (HDV) RNA and of woodchuck hepatitis virus (WHV) DNA and WHV RNA were studied in nonneoplastic liver (NL) tissues, hepatocellular carcinoma (HCC) tissues, and several extrahepatic tissues of chronic WHV carrier woodchucks acutely (two animals) and chronically (six animals) superinfected with HDV. HDV was shown to replicate in all NL and HCC tissues but not in any of the extrahepatic tissues analyzed, which included spleen, peripheral blood lymphocytes, kidney, ovary, testis, thymus, lung, and stomach. HDV RNA was present as species with molecular weights consistent with those of monomers, dimers, and trimers of both strand polarities, supporting the rolling circle model proposed for HDV RNA replication. WHV DNA levels in NL, HCC, spleens, and serum were 10- to 100-fold lower than the levels typically observed in chronic WHV carrier woodchucks not infected with HDV. WHV DNA replicative intermediates were rarely observed and only at very low levels, representing less than 10% of the total WHV DNA. By contrast, WHV RNA transcription was not significantly depressed and both primary WHV RNA transcripts, 2.3 and 3.6 kilobases, were observed in NL, HCC, spleens, and in one of the kidney tissues. In addition, a 2.6-kilobase WHV RNA transcript was found in the majority of the NL tissues.

Animals↗
PubMed1986

Isolation and characterization of milk protein nuclear RNAs in rat mammary gland.

Methods have been developed to isolate high-molecular-weight pre-mRNAs from lactating mammary gland, a tissue high in RNase levels. These methods involved isolation of nuclei at -20 degrees C in 50% glycerol, and nucleic acid extraction using a guanidine thiocyanate-CsCl protocol. Specific RNAs were detected using alpha-, beta-, and gamma-casein and whey acidic protein nick-translated cDNA and genomic DNA probes by hybridization in situ to pre-mRNAs fractionated on agarose gels containing 10 mM methylmercuric hydroxide. Using these techniques it was possible to isolate poly(A)-containing gene-sized primary transcripts in the case of the two smaller genes, beta-casein and whey acidic protein. A very complex pattern of pre-mRNAs was observed for the beta-casein transcripts, including detection of a species which may represent an excised intron. Probes for the alpha- and gamma-casein genes revealed much lower abundance and complexity of RNA precursors. These methods have proven useful in the initial analysis of RNA processing of these hormonally regulated milk protein gene transcripts.

Animals↗
PubMed1986

Plague.

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Humans↗
PubMed1985

The rat casein multigene family. Fine structure and evolution of the beta-casein gene.

Eight overlapping phage clones, spanning 34.4 kilobase pairs of genomic DNA, containing the 7.2-kilobase pair rat beta-casein gene have been isolated and characterized. The first 510 base pairs (bp) of 5' flanking, 110 bp of 3' flanking, and all the exon/intron junctions have been sequenced. The beta-casein gene contains 9 exons ranging in size from 21 to 525 bp. We have attempted to identify potential regulatory elements by searching for regions of sequence homology shared between milk protein genes which respond similarly to lactogenic hormones and by searching for previously reported hormone receptor-binding sites. Within the conserved first 200 bp of 5' flanking sequences 3 regions of greater than 70% homology were observed between the rat beta- and gamma-casein genes. One of these contains a region 90% homologous to the chicken progesterone receptor-binding site. The conserved 5' noncoding region, the highly conserved signal peptide, and the hydrophobic carboxyl-terminal region of the protein are each encoded by a separate exon. In contrast the evolutionarily conserved phosphorylation site of beta-casein is formed by an RNA-splicing event. The exons which encode the phosphorylation sites of beta-casein appear to have resulted from an intragenic duplication. Based upon the exon structure of the casein genes, an evolutionary model of intragenic and intergenic exon duplications for this gene family is proposed.

Animals↗
PubMed1981

Detection of alpha-amylase activity in unprocessed preamylase produced in the cell-free translation of porcine pancreatic RNA.

Preamylases, synthesized in the RNA-dependent rabbit reticulocyte lysate translation system supplemented with porcine pancreatic RNA were identified by their specific immunoprecipitation with anti-amylase. The preamylases have apparent Mr = 55,000 and 58,000 as compared to 52,000 and 55,000 for the purified, secreted alpha-amylase isozymes. In order to establish whether the unprocessed precursors may assume enzymatically active conformations, we have explored a highly sensitive activity gel electrophoresis technique, by which picogram quantities of enzyme can be detected. When standard alpha-amylase and translation products are subjected to electrophoresis on polyacrylamide gel containing 0.01% starch and CaCl2, active amylase which binds tightly to starch can only migrate as the starch is hydrolyzed. When the gel is subsequently stained with I2, the appearance of clear tracks, the lengths of which are roughly proportional to the logarithm of amylase concentration, signifies the presence of amylase activity. By this approach, we were able to detect amylase activity in a range corresponding to about 100 pg of pure amylase/10 microliters of translation mixture. This value agrees well with an estimate from radioactivity incorporation of total preamylase in the translation mixture, and we consequently conclude that unprocessed preamylase can assume the appropriate conformation to give enzymatic activity.

Amylases↗