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Biomedical subjects

L Ho

Publications and source records attributed to L Ho.

At least 127 records · Page 7Linked to original sources
PubMed1989

Influence of age and testosterone levels on masculine development in rams.

Fifty wethers and 51 spring-born rams were divided into five groups and slaughtered at different seasons of the year at average ages of 271, 361, 459, 557 or 652 d to determine the age and season at which differences in secondary sex characteristics could be detected. Serum testosterone concentrations and testes weights were low in January when the rams were 271 d of age and again in April at 361 d of age. By July, at 459 d of age, testosterone concentrations and testes weights had peaked and then decreased the following November at 557 d and February at 652 d. In contrast with plasma testosterone concentrations and testes weights, buckiness scores, splenius to semimembranosus or semitendinosus muscle ratios, splenius muscle weights and neck and shoulder percentages were not seasonal. All of these measures increased significantly up to July and continued to increase slowly, but not significantly, thereafter. Muscle color and texture scores and rib eye color scores tended to increase in a linear manner for both rams and wethers as age increased. Subcutaneous fat from rams was yellower and softer than that from wethers over all age groups. Ram fat firmness did not change (P greater than .05) with age, and the only significant change in ram fat color was between the groups at 271 and 361 d of age. Overall, season of year coupled with higher levels of serum testosterone was related to initial development of secondary sex characteristics in ram lambs.

Adipose Tissue↗
PubMed1989

Influence of gender, breed and age on maturity characteristics of sheep.

Fifty-one ewes, 50 wethers and 51 rams of Finn x whiteface or Suffolk x whiteface breeding were slaughtered at an average age of 271, 361, 459, 557 or 652 d to study changes in maturity characteristics with changes in age. When metacarpal epiphyseal cartilage (growth plates) ossifies with age, break joints on the distal end of the metacarpals fuse and the end of the bone then appears as a spool joint rather than as a break joint. This fusion occurs earlier chronologically in ewes than in rams or wethers. Most Finn x whiteface-cross ewes, which normally reach reproductive maturity earlier than Suffolk x whiteface-cross ewes, exhibited ossified metacarpal growth plates by 459 d of age; break joints of Suffolk x whiteface crosses were not fused until 557 d of age. Both breed groups of rams exhibited fused joints by 557 d of age, but only 3 of 10 wethers exhibited spool joints at 652 d of age. Microscopic examination showed that even in these three wethers the epiphyseal growth plate could still be detected. Yearling 2-yr-old classifications of sheep from teeth were not gender-dependent within the discrete age classes of this study. About half the sheep in each gender group were classified as yearlings at 459 d of age and about half in each group were classified as 2-yr-olds by 652 d of age. Stepwise multiple regression equations to estimate age of sheep in days were developed. Overall maturity, lean color and texture and rib bone maturity were the best carcass measures of maturity. Maturity scores for characteristics of the break joint did not enter any of the equations studied. When eye lens weight was included in equations with the best measures of carcass maturity, accuracy of estimates for age of sheep was improved.

Age Determination by Teeth↗
PubMed1989

Febrile convulsion--a clinical survey and a review of its current concept of management.

Between February 1986 to November 1986, 335 cases of febrile convulsion were admitted to the paediatric ward, Tan Tock Seng Hospital. The study revealed 87 cases (26%) were complex febrile convulsion and 73 cases (21.8%) were recurrent febrile convulsion. 51 patients with complex febrile convulsion and 32 patients with recurrent febrile seizures were put on long term phenobarbitone. The number of patients with recurrent and complex convulsion was big. The role of anticonvulsant prophylaxis is reviewed and its efficacy discussed.

Child↗
PubMed1988

Nucleotide sequence of a cDNA for the dihydrolipoamide acetyltransferase component of human pyruvate dehydrogenase complex.

Deoxynucleotide sequencing of a cDNA for the dihydrolipoamide acetyltransferase (PDC-E2) component of human pyruvate dehydrogenase complex (PDC) revealed an open reading frame of 1848 base pairs corresponding to a leader sequence of 54 amino acids and a mature protein of 561 amino acids (59,551 Da). Both an amino-terminal lipoyl-bearing domain and a carboxy-terminal catalytic domain are present in the deduced amino acid sequence. The lipoyl-bearing domain contains two repeating units of 127 amino acids, each harboring one lipoic acid-binding lysine. Thus, mammalian PDC-E2 differs as to the number of lipoic acid-binding sites from other dihydrolipoamide acyltransferases in both prokaryotic and eukaryotic organisms.

Acetyltransferases↗
PubMed1988

Identification of a cDNA clone for the beta-subunit of the pyruvate dehydrogenase component of human pyruvate dehydrogenase complex.

We report the isolation of a 1.5 kb cDNA clone for the beta subunit of human pyruvate dehydrogenase (E1) from a human liver lambda gt11 cDNA library using anti-E1 serum. We generated a peptide sequence of 24 amino acids starting from the N-terminus of bovine heart mature E1 beta. The identity of the E1 beta cDNA clone was confirmed by the similarity between the amino acid sequence deduced from the cDNA nucleotide sequence and the known amino acid sequence of bovine heart E1 beta. In Northern analysis of total RNA extracted from human heart, the E1 beta cDNA clone hybridized to a major 1.6 kb and a minor 5.2 kb RNA species.

Amino Acid Sequence↗
PubMed1988

Nuclear factors in B lymphoma enhance splicing of mouse membrane-bound mu mRNA in Xenopus oocytes.

Regulation of the synthesis of membrane-bound and secreted immunoglobulin mu heavy chains at the level of RNA processing is an important element for B cell development. The precursor mu RNA is either polyadenylated at the upstream poly(A) site (for the secreted form) or spliced (for the membrane-bound form) in a mutually exclusive manner. When the mouse mu gene linked to the SV40/HSV-TK hybrid promoter was microinjected into Xenopus oocytes, the mu messenger RNA (mRNA) was altered by coinjection of nuclei of mouse surface IgM-bearing B-lymphoma cells to include the synthesis of the membrane-bound form. An increase in the membrane-bound form was not observed when nuclei of IgM-secreting hybridoma cells or fibroblast cells were coinjected. Deletion of the upstream poly(A) site did not eliminate the effect of B-lymphoma nuclei suggesting that membrane-specific splicing is stimulated. Further, splicing of other mu gene introns was not affected by coinjection of B-lymphoma nuclei. These results suggest that mature B cells contain one or more transacting nuclear factors that stimulate splicing specific for membrane-bound mu mRNA.

Animals↗
PubMed1988

Heterogeneous expression of protein and mRNA in pyruvate dehydrogenase deficiency.

Deficiency of pyruvate dehydrogenase [pyruvate:lipoamide 2-oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1], the first component of the pyruvate dehydrogenase complex, is associated with lactic acidosis and central nervous system dysfunction. Using both specific antibodies to pyruvate dehydrogenase and cDNAs coding for its two alpha and beta subunits, we characterized pyruvate dehydrogenase deficiency in 11 patients. Three different patterns were found on immunologic and RNA blot analyses. (i) Seven patients had immunologically detectable crossreactive material for the alpha and beta proteins of pyruvate dehydrogenase. (ii) Two patients had no detectable crossreactive protein for either the alpha or beta subunit but had normal amounts of mRNA for both alpha and beta subunits. (iii) The remaining two patients also had no detectable crossreactive protein but had diminished amounts of mRNA for the alpha subunit of pyruvate dehydrogenase only. These results indicate that loss of pyruvate dehydrogenase activity may be associated with either absent or catalytically inactive proteins, and in those cases in which this enzyme is absent, mRNA for one of the subunits may also be missing. When mRNA for one of the subunits is lacking, both protein subunits are absent, suggesting that a mutation affecting the expression of one of the subunit proteins causes the remaining uncomplexed subunit to be unstable. The results show that several different mutations account for the molecular heterogeneity of pyruvate dehydrogenase deficiency.

Acidosis, Lactic↗
PubMed1988

A deficiency of both subunits of pyruvate dehydrogenase which is not expressed in fibroblasts.

Pyruvate dehydrogenase complex (PDC) deficiency usually has been detected by decreased activity in cultured skin fibroblasts. We investigated two brothers in whom PDC activity was less than 10% of controls in lymphocytes but normal in skin fibroblasts. They both had abnormal neuromuscular development and lactic acidosis which was aggravated by ingestion of carbohydrate. One brother died at age 3 yr and tissues were obtained at autopsy soon after death. The brain was swollen with diffuse acute hemorrhages but without the lesions characteristic of Leigh's disease. PDC activity was virtually undetectable in mitochondria or homogenates of liver, skeletal muscle, and heart, but was about 30% of controls in kidney. The activity of the first component E1 was not detectable in mitochondria from liver, whereas the activities of the second and third components were normal; the activities of all components were normal in fibroblasts. Western immunoblot analysis showed absent to trace amounts of both the E1 alpha and E1 beta subunits in liver, skeletal muscle, and heart, with normal amounts of the second and third components. About one-fourth of control amounts of E1 alpha and E1 beta were present in kidney and normal levels were present in fibroblasts. PDC activity in lymphocytes from the mother was 35% of controls; she had normal PDC activity in her fibroblasts. PDC activity was normal in lymphocytes from the brothers' sister, father, and maternal grandparents and great-grandmother. The mode of inheritance was not established. In conclusion, PDC deficiency may not be detected in skin fibroblasts in some cases; the mechanism of variable tissue expression of E1 remains to be delineated.

Child, Preschool↗
PubMed1987

Isolation of a cDNA clone for the dihydrolipoamide acetyltransferase component of the human liver pyruvate dehydrogenase complex.

Dihydrolipoamide acetyltransferase (E2) forms the structural core of pyruvate dehydrogenase complex. A cDNA clone (lambda E2-1) for mammalian E2 was identified from a human liver lambda gt11 library using anti-E2 serum. Affinity-selected antibodies using the fusion protein from lambda E2-1 immuno-reacted specifically with E2 of purified pyruvate dehydrogenase complex on immuno-blot analysis. The cDNA insert was approximately 2.3 kb in length with an internal EcoR1 site generating 1.4 and 0.9 kb fragments. A synthetic 17-mer oligodeoxynucleotide mixture based on the amino acid sequence surrounding the lipoic acid-containing lysine residue in bovine kidney E2 hybridized with the 2.3 kb cDNA insert and the 1.4 kb fragment.

Acetyltransferases↗
PubMed1987

Malignant parotid gland tumors: a retrospective study.

This is a comprehensive retrospective study (1965-1984) of 130 patients with malignant parotid gland tumors. Patients were studied by comparison of presenting symptoms, histopathologies, treatments, disease-free intervals, and ultimate intervals. Facial paralysis was noted on presentation in 23% of the cases and regional neck node metastases were noted in 13%. Both findings correlated with prognosis. Seventy patients underwent surgery alone and 30 patients received combined therapy. The remaining patients were excluded from the study. The overall 5-year survival rate was 50%, with a 44% risk of recurrence. Fifty-six percent of the patients whose conditions subsequently recurred had their facial nerves sacrificed at time of surgery. Selected patients who received combined therapy experienced better local regional control and a prolonged disease-free interval as compared with those who underwent surgery alone. Combined therapy, however, provided no survival benefit for this group of patients. Adjuvant radiation therapy is recommended in the treatment planning of selected malignant tumors of the parotid gland.

Adenocarcinoma↗
PubMed1987

Systemic deficiency of the first component of the pyruvate dehydrogenase complex.

An infant with lactic acidosis and developmental delay had neuropathological changes consistent with Leigh's necrotizing encephalomyelopathy. Total pyruvate dehydrogenase complex (PDC) activity was low relative to controls in lymphocytes (0.2 versus 1.9 +/- 0.6 SD nmol/min/mg protein) and cultured skin fibroblasts (0.9 versus 2.7 +/- 1.0). Liver, muscle, heart, and kidney mitochondria oxidized several substrates normally, but did not oxidize pyruvate. PDC activity was absent in these mitochondria (0.1 versus 9.8 +/- 4.2 in liver and 0.7 versus 75 +/- 26 in muscle) and was very low in all tissue homogenates. Activity of the first component was low in liver mitochondria, whereas activities of the second and third components were normal. Western blot analysis of tissue proteins showed normal amounts of second and third component of PDC but undetectable to trace amounts of both alpha and beta subunits of the first component of PDC in liver, brain, kidney, heart, and skin fibroblasts. Thus, profound systemic deficiency of PDC was due to lack of both subunit proteins of the first component of PDC.

Fibroblasts↗
PubMed1986

Characterization of a DNA repair domain containing the dihydrofolate reductase gene in Chinese hamster ovary cells.

The formation and removal of UV-induced pyrimidine dimers were measured in restriction fragments near and within the essential dihydrofolate reductase (DHFR) gene in Chinese hamster ovary cells in order to map the genomic fine structure of DNA repair. Dimer frequencies were determined at 0, 8, and 24 h after irradiating the cells with 20 J/m2 UV light (254 nm). Within 8 h, the cells had removed more than 40% of the dimers from sequences near the 5' end of the gene, somewhat fewer from the 3' end, but only 2% from the 3' flanking region and 10% from a region upstream from the gene. The corresponding extent of repair in the genome as a whole is 5-10% in the 8-h period. Isoschizomeric restriction enzyme analysis was used to detect the level of methylation in the fragments in which repair was measured. We found that the only hypomethylated sites in and around the DHFR gene were in the fragment near its 5' end, which displayed maximal DNA repair efficiency. The size of the region of preferential DNA repair at the DHFR locus appears to be in the range of 50-80 kilobases, and this finding is discussed in relation to genomic domains and the structure of mammalian chromatin.

Animals↗
PubMed1986

Insulin action is blocked by a monoclonal antibody that inhibits the insulin receptor kinase.

Thirty-six monoclonal antibodies to the human insulin receptor were produced. Thirty-four bound the intracellular domain of the receptor beta subunit, the domain containing the tyrosine-specific kinase activity. Of these 34 antibodies, 33 recognized the rat receptor and 1 was shown to precipitate the receptors from mice, chickens, and frogs with high affinity. Another of the antibodies inhibited the kinase activities of the human and frog receptors with equal potencies. This antibody inhibited the kinase activities of these receptors by more than 90%, whereas others had no effect on either kinase activity. Microinjection of the inhibiting antibody into Xenopus oocytes blocked the ability of insulin to stimulate oocyte maturation. In contrast, this inhibiting antibody did not block the ability of progesterone to stimulate the same response. Furthermore, control immunoglobulin and a noninhibiting antibody to the receptor beta subunit did not block this response to insulin. These results strongly support a role for the tyrosine-specific kinase activity of the insulin receptor in mediating this biological effect of insulin.

Animals↗
PubMed1986

Deficiency of the pyruvate dehydrogenase component in pyruvate dehydrogenase complex-deficient human fibroblasts. Immunological identification.

A previously reported deficiency of "total" pyruvate dehydrogenase complex activity is further characterized. Dihydrolipoyl transacetylase (E2) and lipoamide dehydrogenase (E3) activities in the patient's fibroblasts were normal. Pyruvate dehydrogenase activity (E1) was 33% of that in fibroblasts from an age-matched control. The amounts of each of the components of pyruvate dehydrogenase complex were analyzed using an immunoblot technique and specific antibodies. Levels of components E2 and E3 were the same in fibroblasts from the patient and control, confirming the activity measurements. However, the levels of E1 alpha and E1 beta were reduced markedly in fibroblasts from the patient. Thus, impairment in the pyruvate dehydrogenase complex activity was due to a reduction in the amount of the E1 component of the complex.

Acetyltransferases↗