PubMed Health⌕ Search

Biomedical subjects

C L Thomas

Publications and source records attributed to C L Thomas.

At least 55 records · Page 3Linked to original sources
PubMed1991

Desmosomal glycoprotein DGI, a component of intercellular desmosome junctions, is related to the cadherin family of cell adhesion molecules.

Among the variety of specialized intercellular junctions, those of the adherens type have the most obvious association with cytoskeletal elements. This may be with the actin microfilament system as in the zonula adherens or with intermediate filaments as in the macula adherens, or desmosome. In the former case, it is clear that transmembrane glycoproteins of the cadherin family are important adhesive components of the molecular assembly. We now show for desmosomes that a major glycoprotein component (desmosomal glycoprotein DGI) has extensive homology with the cadherins, defining an extended family, but also has unique features in its cytoplasmic domain that are likely to be relevant to the association with intermediate rather than actin filaments. A novel 282-residue extension contains repeats of approximately 29 amino acid residues predicted to have an antiparallel beta-sheet structure, followed by a glycine-rich sequence. As in the cadherins, the extracellular domain contains possible Ca2(+)-binding sequences and a potential protease processing site. The cell adhesion recognition region (His-Ala-Val) of the cadherins is modified to Arg-Ala-Leu.

Amino Acid Sequence↗
PubMed1990

Beta-galactosidase decreases the binding affinity of the insulin-like-growth-factor-II/mannose-6-phosphate receptor for insulin-like-growth-factor II.

The insulin-like growth-factor-II/mannose-6-phosphate (IGF-II/Man6P) receptor binds two classes of ligands, insulin-like growth factors and lysosomal enzymes. We have examined the ability of the lysosomal enzyme, beta-galactosidase, to modulate the binding of 125I-IGF-II to the receptor. beta-Galactosidase purified from bovine testis was fractionated on a DEAF-Sephacel ion-exchange column. Column fractions were assayed for enzymatic activity and for ability to inhibit the binding of 125I-IGF-II to the IGF-II/Man6P receptor. Enzyme fractions eluting at higher NaCl concentrations which had previously been shown to exhibit greater uptake by cells in culture, exhibited greater potency in inhibiting the binding of 125I-IGF-II to the receptor. A pool of these fractions from the DEAE-Sephacel column inhibited 125I-IGF-II binding to pure receptor by 80% with the concentration required for half-maximal inhibition being 25 nM. The inhibition of binding by beta-galactosidase was completely blocked by simultaneous incubation with Man6P. Inhibition of the enzymatic activity of beta-galactosidase with D-galactonic acid gamma-lactone did not affect the ability of beta-galactosidase to inhibit the binding of 125I-IGF-II to the receptor. Scatchard analysis of IGF-II binding to pure receptor in the presence and absence of beta-galactosidase showed that beta-galactosidase decreased the binding affinity for IGF-II (Kd 0.26 nM versus 1.0 nM in the presence of 57 nM beta-galactosidase). We confirmed the observations of others that Man6P alone actually increases the binding of 125I-IGF-II to the IGF-II/Man6P receptor, but we found that this phenomenon was dependent upon the method of preparation of the IGF-II/Man6P receptor. Microsomal membrane preparations, solubilized membranes, and receptors purified on an IGF-II-Sepharose column all exhibited stimulation of 125I-IGF-II binding by Man6P, whereas receptors purified on lysosomal enzyme affinity columns showed little or no stimulation of 125I-IGF-II binding by Man6P. We conclude that beta-galactosidase decreases the binding affinity of the IGF-II/Man-6-P receptor for IGF-II by binding with high affinity to the Man6P-recognition site.

Animals↗
PubMed1989

Developmental expression of the tissue insulin-like growth factor II/mannose 6-phosphate receptor in the rat. Measurement by quantitative immunoblotting.

We used quantitative immunoblotting to measure the total tissue insulin-like growth factor II/mannose 6-phosphate (IGF-II/Man-6-P) receptor in the rat. Whole embryos (6-15 days of gestation) and tissues from 16- and 20-day-old fetal and 5-, 10-, 20-, and 40-day-old postnatal rats were placed in liquid nitrogen, extracted with 2% Triton X-100, and boiled in 2% sodium dodecyl sulfate. The extracts were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis together with aliquots of a highly purified rat IGF-II/Man-6-P receptor standard. The protein bands were transferred from the gel to nitrocellulose sheets by electroelution. The nitrocellulose sheets were incubated with a specific IGF-II/Man-6-P receptor antiserum (3637). The immunoblots were developed with 125I-protein A and an immunoperoxidase stain. Stained areas were cut from the immunoblots, and radioactivity was measured in a gamma-counter. IGF-II/Man-6-P receptor levels were high in fetal tissues and in most tissues declined dramatically in late gestation and/or in the early postnatal period. Concentrations in 16-day-old fetal tissues, expressed as percent of total protein in the extract, were: heart, 1.7; placenta, 1.0; lung, 0.7; intestine, 0.7; muscle, 0.5; kidney, 0.5; liver, 0.3; and brain, 0.1. In whole embryos (6-15 days of gestation), the IGF-II/Man-6-P receptor ranged between 0.1 and 0.4% of total protein in the extract. The IGF-II/Man-6-P receptor size varied within approximately 20 kDa among different tissues and also varied with developmental age in the same tissue. We conclude that the IGF-II/Man-6-P receptor is a major cellular protein in some fetal tissues and that the developmental pattern of receptor expression suggests that the receptor plays an important role in fetal growth and development.

Aging↗
PubMed1989

Insulin-like growth factor-II (IGF-II) inhibits both the cellular uptake of beta-galactosidase and the binding of beta-galactosidase to purified IGF-II/mannose 6-phosphate receptor.

The insulin-like growth factor-II/mannose 6-phosphate receptor which targets acid hydrolases to lysosomes, has two different binding sites, one for the mannose 6-phosphate (Man-6-P) recognition marker on lysosomal enzymes and the other for insulin-like growth factor-II (IGF-II). We have asked whether IGF-II can regulate the cellular uptake of the lysosomal enzyme 125I-beta-galactosidase by modulating the binding of 125I-beta-galactosidase to the IGF-II/Man-6-P receptor. We first isolated high affinity 125I-beta-galactosidase by affinity chromatography on an IGF-II/Man-6-P receptor-Sepharose column. Specific uptake (mannose 6-phosphate-inhibitable) of 125I-beta-galactosidase in BRL 3A2 rat liver cells and in rat C6 glial cells was 3.7-4.8 and 4.0-8.0% of added tracer, respectively. The cell-associated 125I-beta-galactosidase in the uptake experiments largely represented internalized radioligand as measured by acid or mannose 6-phosphate washing. The uptake of 125I-beta-galactosidase was inhibited by an antiserum (No. 3637) specific for the IGF-II/Man-6-P receptor. Low concentrations of IGF-II also inhibited the uptake of 125I-beta-galactosidase. Maximal concentrations of IGF-II inhibited uptake by 73 +/- 8% (mean +/- S.D.) in C6 cells and by 77 +/- 6% in BRL 3A2 cells compared to the level of inhibition by mannose 6-phosphate. The relative potency of IGF-II, IGF-I, and insulin (IGF-II much greater than IGF-I; insulin, inactive) were characteristic of the relative affinities of the ligands for the IGF-II/Man-6-P receptor. IGF-II also partially inhibited the binding of 125I-beta-galactosidase to C6 and BRL 3A2 cells at 4 degrees C and inhibited the binding to highly purified IGF-II/Man-6-P receptor by 58 +/- 14%. We conclude that IGF-II inhibits the cellular uptake of 125I-beta-galactosidase and that this inhibition is partly explained by the ability of IGF-II to inhibit binding of 125I-beta-galactosidase to the IGF-II/Man-6-P receptor.

Animals↗
PubMed1988

Mutations within the decoding site of Escherichia coli 16S rRNA: growth rate impairment, lethality and intragenic suppression.

Several C----U transitions and small deletions were introduced into the conserved region centered on base C1400 in Escherichia coli 16S rRNA by in vitro mutagenesis. The mutations were placed within rrnB operons on multicopy plasmids under the transcriptional regulation of either the normal rrnB P1P2 promoters or the temperature-inducible PL promoter from bacteriophage lambda and introduced into E. coli hosts. When expressed from the P1P2 promoters, several of the mutant 16S rRNAs impaired cell growth while others, including one in which U replaced C at position 1400 within the ribosomal decoding site, had little or no effect on cell doubling time. However, C----U transitions at positions 1395 and 1407, as well as the deletion of C1400, appeared to render their hosts inviable. Cells in which these mutations were expressed from the lambdaPL promoter died within four generations after induction. Unexpectedly, the lethal phenotype was suppressed intragenically by replacement of G1505 with A, C or U. Suppression may alleviate a functional defect in 30S subunits containing the U1395, U1407 or deltaC1400 mutations.

Base Sequence↗
PubMed1988

Biochemical evidence that the type II insulin-like growth factor receptor is identical to the cation-independent mannose 6-phosphate receptor.

Cloning and sequencing of the human type II insulin-like growth factor (IGF) receptor cDNA revealed an 80% deduced amino acid sequence homology with the bovine cation-independent mannose 6-phosphate (Man-6-P) receptor, suggesting identity of the two receptors (Morgan, D. O., Edman, J. C., Standring, D. N., Fried, V. A., Smith, M. C., Roth, R. A., and Rutter, W. J. (1987) Nature 329, 301-307). We have performed biochemical experiments that support this proposal. Rat liver type II IGF receptor, purified by the conventional method of IGF-II affinity chromatography, bound quantitatively to a beta-galactosidase affinity column and was eluted with Man-6-P. Bovine liver Man-6-P receptor, prepared by the conventional method of affinity chromatography on phosphomannan-Sepharose, bound IGF-II with high affinity (Kd = 1 nM). Affinity cross-linking of 125I-IGF-II to the Man-6-P receptor and analysis by sodium dodecyl sulfate-gel electrophoresis showed that beta-galactosidase, but not Man-6-P, inhibited the formation of the 250-kDa 125I-IGF-II-receptor complex. The inhibition by beta-galactosidase was prevented by coincubation with Man-6-P. 125I-IGF-II did not bind to the 46-kDa cation-dependent Man-6-P receptor. For immunologic studies we purified type II IGF receptors and Man-6-P receptors in parallel from rat placental membranes using either IGF-II- or beta-galactosidase affinity chromatography. A panel of five antisera that previously had been raised against either type II IGF receptor or Man-6-P receptor behaved identically toward type II IGF receptor versus Man-6-P receptor in ligand blocking and immunoprecipitation assays. Our data support the conclusion that the type II IGF receptor and the cation-independent Man-6-P receptor are the same protein and that the IGF-II and Man-6-P-binding sites are distinct.

Animals↗
PubMed1986

Characteristics of thyroxine 5'-deiodinase activity in human liver.

The conversion of thyroxine (T4) to triiodothyronine (T3) was studied in homogenates and subcellular fractions of 10 human liver specimens obtained postmortem. Preliminary studies indicated that T4 5'-deiodinase activity did not decline in rat liver kept at 5 degrees C for 6 and 24 hr after death. All human liver homogenates but one catalyzed T3 production, although the quantity of T3 produced varied greatly, from 8-fold in the absence of dithiothreitol (DTT) to 100-fold in its presence. The wide variation in activity found may reflect either postmortem loss or premortem decline in enzyme activity due to unrecognized nonthyroidal illness. The amount of T3 produced was dependent on substrate availability, protein concentration, time, pH and temperature, and enzyme activity was greatest in the microsomal fraction. T3 production was stimulated by DTT and inhibited by propylthiouracil (PTU). Thus, human liver T4 5'-deiodinase has properties very similar to the same enzyme in rat liver. These data suggest that results of studies of the effects of nonthyroidal illnesses and drugs on T4 5'-deiodinase activity in rat liver may be extrapolated to humans.

Adolescent↗
PubMed1985

Prostaglandin production by rat vaginal tissue, in vitro, in response to ethanol, a mild mucosal irritant.

Toxicological testing of vaginal irritants currently involves in vivo testing in rabbits. While chemical-induced irritation or inflammation involves numerous biologic responses, these responses appear to be to a large extent mediated by prostaglandin release. Since vaginal tissue of the rat produces prostaglandins, this tissue was studied in vitro to determine if it would respond to ethanol, a mild irritant. Small vaginal segments were rinsed in Krebs-Ringer bicarbonate buffer (pH 7.0) and exposed to various concentrations of ethanol. The segments were then transferred to fresh buffer and incubated for 30 min in a shaking 37 degrees C water bath. Ethanol (70%) exposure for 30 sec increased prostaglandin E2 and F2 alpha production by vaginal tissue. While ethanol exposure resulted in increases in prostaglandin production regardless of the stage of the cycle from which the tissue was derived, the relative increase was greatest in tissues from the diestrous stage of the cycle. The prostaglandin production response of vaginal tissue, and of cervical and uterine tissue, was related to the concentration of ethanol to which these tissues were exposed. Indomethacin blocked this response in a dose-dependent manner. These experiments demonstrate that vaginal tissue responds to ethanol by increasing production of PGF2 alpha and PGE2. This in vitro system may prove useful as an alternative to live-animal testing in the screening of irritants of the vaginal mucosa or other tissues as well.

Animals↗
PubMed1985

Components of genetic variance and covariance for linear type traits in Jersey cattle.

First available appraisals for 67,644 Jersey cows were used to estimate relative magnitudes of additive and selected sources of nonadditive genetic variance and covariance for 13 type traits scored linearly from 50 to 99 points. Covariances among four types of relatives were used to estimate components of genetic variance and covariance for each of the 13 traits. Direct additive, direct dominance, and additive maternal genetic variances and the direct-maternal additive genetic covariance were estimated using covariances among paternal half-sibs, full-sibs, daughters and dams, and maternal half-sibs. Estimates of additive genetic variance were 11 to 36% of variance within herd-appraiser subclasses with largest values for stature, strength, rump angle, rump width, and udder depth. Dominance components were two to four times the magnitude of additive components for dairy character, rump width, fore udder, rear udder height, rear udder width, and suspensory ligament but much smaller for other traits. Maternal effects and the direct-maternal additive genetic covariance appeared small for all linear type traits.

Animals↗
PubMed1984

Complete suppression of plasma follicle-stimulating hormone in castrated male and female rats during continuous administration of porcine follicular fluid.

The effects of continuous i.v. infusion of porcine follicular fluid (PFF), presumed to contain inhibin activity, on plasma gonadotropin levels were investigated in adult male and female Sprague-Dawley rats. One group each of male and female rats was castrated just prior to the start of treatment of 10-day duration (ACUTE). Another ACUTE group of females was treated for 30 days. A final group of female rats was ovariectomized 3 months before the start of treatment of 10-day duration (CHRONIC). When administered at a dosage of 1.0 mg/100 g body weight/24 h, charcoal-extracted PFF suppressed plasma follicle-stimulating hormone (FSH) concentrations to hypophysectomy levels within 48 h and maintained these levels for 10 days in all groups treated. In the ACUTE group of female rats treated for 30 days, FSH suppression was maintained during infusion up to 20 days. This inhibition became attenuated after 25 days of treatment and completely disappeared by 30 days. There was no discernible effect of PFF on luteinizing hormone (LH) concentrations at any time. Upon cessation of PFF treatment at 10 days in both ACUTE and CHRONIC ovariectomized rats, FSH levels rebounded to normal ovariectomy control concentrations within 2-4 days. Porcine serum (PS) was similarly extracted and administered as a control substance. It exerted no detectable effect on either FSH or LH concentrations in ACUTE or CHRONIC castrated rats. These results demonstrate that PFF alone is capable of maximally suppressing FSH secretion when administered by continuous infusion. This finding is especially significant considering that such a pronounced effect was obtained in the total absence of gonadal steroids.

Animals↗
PubMed1984

Relationships between linear type scores, objective type measures, and indicators of mastitis.

Objectives were to examine the usefulness of objective measures of conformation and linear scores for type for predicting indicators of mastitis. Approximately 300 cows in five herds were scored in the experimental linear classification program of the Holstein-Friesian Association of America, measured objectively for numerous components of conformation, and evaluated for four indicators of mastitis. Indicators of mastitis were average natural logarithm of somatic cell counts during the lactation, percent of samples (taken approximately every 3 mo) infected during a lactation, percent of samples infected with Staphylococcus aureus, Streptococcus agalactiae, Escherichia coli, Klebsiella, and percent of samples with signs of mastitic milk. Relationships between conformation and mastitis often were inconsistent because of moderate or low correlations between indicators of mastitis. Indicators of mastitis were predicted from results of multiple regression analyses with subjective scores and objective measures of type as independent variables. Largest differences of predicted indicators of mastitis from variation in any single type trait were sufficient to be important economically, but average differences were much smaller. Selection to reduce frequencies of cows with deep udders, especially low rear udders, widely placed teats, rear teats too far back, and teats that are short and wide, may augment, modestly, efforts to reduce incidence of mastitis through improved sanitation, antibiotic treatment, and proper milking procedures.

Animals↗
PubMed1982

Treatment concepts for proximal femoral ischemic necrosis complicating congenital hip disease.

A retrospective review of fifty-three congenitally dislocated hips (in forty-four patients) in which ischemic necrosis developed was undertaken to assess patterns of growth disturbance and to establish treatment protocols. We utilized the Bucholz and Ogden classification of the four roentgenographic patterns of ischemic necrosis complicating the treatment of congenital hip disease. Patients with Type-I disease had transient ischemia with early recovery. Significant growth disturbances requiring surgical treatment were not observed. Limb-length discrepancy, increased height of the greater trochanter relative to the femoral neck and head, and problems with femoral head coverage were more likely to develop in hips with Type-II or Type-III ischemic necrosis. Equalization of limb lengths, trochanteric epiphyseodesis, and surgical means of improving femoral head coverage were also more commonly indicated in these patients. In patients with Type-IV disease, mild deformities of the femoral head and occasional limb-length discrepancies developed; other sequelae were uncommon and surgical intervention was rarely required.

Child, Preschool↗
PubMed1978

Young children's preferences for listening rates.

A paired-comparison paradigm was utilized to determine the preferences of 20 young children for listening rate for prose speech. An electronic expansion/compression technique yielded nine rates of speech ranging from 100 wpm to 200 wpm, with intervals of 25 wpm. The results indicated that the children most preferred a listening rate of 200 wpm and least preferred a rate of 100 wpm. Comparisons of the present findings with preference rates of older, post-adolescent children and adults are discussed. Direction for further research with temporal alteration and linguistic constraints on the message are considered.

Age Factors↗
PubMed1978

Comparison of three methods of differentiating bovine mycoplasma.

Growth inhibition (GI) by specific antisera, direct fluorescent antibody technique (FAT), and fatty-acid profile analysis by gas-liquid chromatography (GLC) were compared as methods for identifying 13 strains of bovine mycoplasma. By the FAT, there were 8 bilateral and 13 unilateral cross reactions. In the GI study, there were 4 bilateral and 7 unilateral cross reactions. In both FAT and GI studies, there were fluorescence and inhibition, respectively, with 13 homologous antisera. Analysis by GLC revealed the 13 mycoplasmas could be placed into 4 distinct chromatographic groupings. The GLC profiles of 2 organisms were sufficiently unique that they could be used for specific identification.

Animals↗