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Biomedical subjects

C Ma

Publications and source records attributed to C Ma.

At least 163 records · Page 9Linked to original sources
PubMed1994

spitz, a Drosophila homolog of transforming growth factor-alpha, is required in the founding photoreceptor cells of the compound eye facets.

Cell type specification and differentiation in the developing Drosophila compound eye begins in the morphogenetic furrow. In the furrow, cells are organized into evenly spaced preclusters and there is a synchronized arrest of the cells' mitotic cycle in G1. We report that recessive spitz loss-of-function mutations affect compound eye development. Spitz is homologous to the human transforming growth factor-alpha. In mosaic clones, spitz function is required in the first photoreceptor cells to differentiate for normal ommatidial development. spitz loss-of-function mutations are dominant suppressors of EgfrE gain-of-function mutations of the epidermal growth factor-receptor gene. These data suggest that the spitz product is a precluster promoting factor. spitz transcription increases abruptly in the morphogenetic furrow, the obverse of Egfr expression. We present a model for the expression of, and cellular requirement for, this growth factor homolog.

Alleles↗
PubMed1994

Condensation of supercoiled DNA induced by MnCl2.

Multivalent cations condense DNA in vitro, but it had been thought that a valence of at least + 3 was required in aqueous solution. We have found that Mn2+ can produce toroidal condensates of supercoiled plasmid DNA, but not of linearized plasmid. Mg2+ does not cause condensation, and neither MgCl2 nor NaCl can negate the effect of MnCl2, indicating that the condensation mechanism with Mn is not primarily electrostatic. Supercoiled MnDNA is more extensively digested than the linear form by S1 nuclease. Supercoiling appears to cooperate with Mn2+ in stabilizing helix distortions and also provides a "pressure" that enhances lateral association.

Chlorides↗
PubMed1994

A perceptual study of source coding of Fourier phase and amplitude of the linear predictive coding residual of vowel sounds.

A practical question in a Fourier transform coding of speech signals is to what accuracy their amplitude and phase spectra have to be represented without perceptible distortions. In this paper a concern is with the audibility of quantization noise signals which are produced by quantizing the amplitude and phase spectra of vowel sounds. Experiments show that the detection of the noise targets with maskers of a low fundamental frequency is determined mainly by the sharpest temporal resolution of the auditory system in the high-frequency region. For maskers of a high fundamental frequency the detection is determined mainly by the sharpest spectral resolution in the low-frequency region. Noise targets with global random phase and amplitude are relatively more difficult to detect than those produced by a local randomization. Local random phase noise targets are generally more detectable than those produced by local amplitude randomization. The relative importance of phase and magnitude spectra in the Fourier transform coding is strongly dependent on the fundamental frequency of the vowel sounds and the window size used in the short-time Fourier analysis.

Auditory Perception↗
PubMed1994

[Regulative effects of electroacupuncture on gastric hyperfunction induced by electrostimulation of the lateral hypothalamus area of rabbits].

This paper reported our observation of the action of acupuncture on the change of gastric function induced by the excitation of the lateral hypothalamus area (LHA, the feeding center), and research on the mechanism of the acupuncture to inhibiting excessive appetite and reducing hunger in obese people. Electroacupuncture at Zusanli (ST 36) or Neiting (ST 44) could inhibit the hyperactivity of the stomach induced by stimulation of LHA (P < 0.05, P < 0.01). The electroacupuncture effect on LHA remained statistically significant (P < 0.05, P < 0.01) 0.5-2.5 hours after acupuncturing. The alpha-receptor blocking agent phentolamine (1mg/kg) was not distinctly affected (P > 0.05) on the inhibition of electroacupuncturing Zusanli (ST 36) to restrain the hyperactivity of the stomach induced by stimulation on LHA; But beta-receptor blocking agent propranolol (0.3mg/kg) could obviously inhibit the effect of electroacupuncturing Zusanli (ST 36) to restrain hyperactivity of stomach triggered by excitation of the LHA. The result shows that electroacupuncture obviously inhibits gastric hyperfunction caused by excitation of the LHA, for as long as over 3 hours, thus indicating the participation of the humoral factors. Since the electroacupuncture at Zusanli (ST 36) only inhibits gastric hyperfunction caused by excitation of the LHA, it is suggested that the electroacupuncture has an anticholinergic effect through the gastric beta receptor, therefore it inhibits the appetite, relieves hunger and reduces body weight in obese people.

Animals↗
PubMed1994

[The effect of acupuncture on the function of macrophages in rats of immunodepression].

The immunodepression model was established by means of intraperitoneal injection of cyclophosphamide in rats. Their phagocytic percentage and phagocytic index of peritoneal macrophages (PM phi) as well as serum lysozyme (LSZ) decreased obviously; After 6 days of acupuncture at "Zusanli" points (ST 36), PM phi phagocytic percentage and phagocytic index increased significantly, Serum LSZ showed no significant change. These results indicate that acupuncture can increase the phagocytic function of M phi in rats of immunodepression, but Serum LSZ level does not synchronously increase with the phagocytic function of M phi.

Acupuncture Therapy↗
PubMed1994

[Experimental comparison of the toxicity of radix Aconity Kusnezoffii and processed radix Aconity Kusnezoffii by different methods].

This paper deals with the effects of Radix Aconity Kusnezoffii and Radix Aconity Kusnezoffii processed by a new method of moistening and steaming, and by pharmacopoeial routine on acute toxicity, cardiac rhythm and respiration. The result shows that the Radix Aconity Kusnezoffii processed by new method No 1., which applies moistening in water for 48h and then heating with high pressure steam (68.65kPa, 115 degrees C) for 2h, has the advantages of lower toxicity, and lesser inhibitory effect on cardiac rhythm and respiration.

Animals↗
PubMed1994

Vesicles and mixed micelles in hypothyroid rat bile before and after thyroid hormone treatment: evidence for a vesicle transport system for biliary cholesterol secretion.

Hypothyroid rats show reduced secretion of biliary lipids, especially cholesterol. Secretion of biliary cholesterol is markedly augmented to levels above euthryroid beginning 12-24 h after administration of thyroid hormone. In the current studies, bile from hypothyroid and triiodothyronine-treated chronic bile-fistula rats was analyzed for vesicles and mixed micelles by metrizamide gradient ultracentrifugation. For euthryoid and hypothyroid animals, less than 12% of biliary cholesterol was in a vesicle gradient fraction. After treatment with triiodothyronine, biliary cholesterol increased markedly, and 50% of total cholesterol, 60% of excess cholesterol secreted, appeared in the vesicle fraction. Triiodothyronine stimulation of vesicle secretion resulted in cholesterol-rich vesicles (cholesterol:phospholipid ratio rose from less than 0.1 to 0.56), but no change in the distinct fatty acid composition of vesicle phospholipids. The microtubule inhibitor colchicine, given 12 h after triiodothyronine, prevented subsequent increase in cholesterol secretion in the form of vesicles. These studies, in a model that allows rapid changes in biliary lipid secretion, support the hypothesis that an important component of cholesterol and phospholipid secretion into bile involves microtubules and may involve a vesicle pathway.

Animals↗
PubMed1994

[Haemorrheological effects of different processed products of radix Aconiti Kusnezoffii on animal model with syndrome of "accumulation of cold and blood stasis"].

The effects of Radix Aconiti Kusnezoffii processed by moistening in combination with steaming method and by pharmacopoeial method as well as of the crude drug on haemorrheological nature and the plasma fibronogen content and platelet aggregation rate in the rat model with syndrome of "accumulation of cold and blood stasis" were studied, the result shows that the product processed by moistening in combination with steaming works best.

Animals↗
PubMed1994

Pathological changes of the retrosplenial cortex in senile dementia of Alzheimer type.

Six brains of patients aged from 71 to 85 years of clinically and pathologically diagnosed senile dementia of Alzheimer type and six brains of age-matched controls (55-91 years) was used for this study. The retrosplenial cortex of these brains have been examined by Gallyas and Campbell-silver impregnations. Gallyas preparation showed a number of intracellular pathological changes in retrosplenial cortex of demented individuals. Although the neuritic plaques, the neurofibrillary tangles and neuropil threads were seen in all lamina, their high density appear in lamina IIIa and V of retrosplenialis lateralis (Rsl), retrosplenialis intermedia (Rsi), retrosplenialis media (Rsm) and parasplenialis (Ps). The retrosplenial cortex of non-demented individuals was almost devoid of neurofibrillary changes. The retrosplenial cortex of all demented individuals and one age-matched controls showed a large amount of amyloid deposits in Campbell preparation, while two non-demented individuals showed only small amounts of amyloid. The amyloid deposition can be classified into three types. The packing of Campbell-argyrophilic material show area-specific and lamina-specific distribution.

Aged↗
PubMed1993

The segment polarity gene hedgehog is required for progression of the morphogenetic furrow in the developing Drosophila eye.

Cell-type specification in the Drosophila compound eye begins at the morphogenetic furrow. The furrow sweeps across the developing eye epithelium and is coincident with four classes of cellular events: coordinated changes in cell shape, changes in gene expression, synchronization of the cell cycle, and the specification of a regular array of ommatidial founder cells. The molecular mechanisms that induce these events in the developing eye have hitherto been unknown. We identify here a gene specifically required for furrow progression, hedgehog (hh). We show that hh expression posterior to the morphogenetic furrow is continuously required for its progression. We propose that forward diffusion of hh protein induces anterior cells to enter the furrow.

Animals↗
PubMed1993

In vitro protein engineering using synthetic tRNA(Ala) with different anticodons.

The use of synthetic tRNA for in vitro protein engineering was tested in a coupled transcription/translation system prepared from Escherichia coli. DNA sequences similar to the natural tRNA(Ala/UGC) gene from E. coli but with different anticodons were synthesized in vitro, cloned into a DNA plasmid, and then transcribed in vitro with T7 RNA polymerase. The UGC alanine anticodon was changed to CUA corresponding to the UAG stop codon, CCU corresponding to the rarely used AGG arginine codon, and two four-nucleotide anticodons used to suppress stop codons. Bacterial dihydrofolate reductase was the test protein. Its cloned coding sequence was mutagenized at the GUG codon for valine-75 to correspond to the anticodons of the tRNA constructs, and then the plasmids were used to direct the synthesis of dihydrofolate reductase in the coupled transcription/translation system containing the corresponding synthetic tRNA. The results indicate that all four synthetic tRNAs were functionally active in the synthesis of full-length, enzymatically active dihydrofolate reductase protein.

Amino Acid Sequence↗
PubMed1993

Endogenous epidermal growth factor regulates limb development.

Mutations associated with genes of the EGF superfamily are implicated in limb malformations. To evaluate the potential role of EGF-mediated signal transduction in the control of early mammalian limb development, we developed a simple in vitro system which is permissive for morphogenesis and cytodifferentiation in serumless, chemically defined medium. Our experimental strategy was to ascertain if the EGF precursor gene was transcribed and translated into potentially bioactive growth factor. EGF mRNA transcripts are expressed in Swiss Webster mouse embryonic (42-44 somite pairs) forelimbs as determined by mRNA phenotyping. EGF transcripts are translated into precursor EGF polypeptides which were localized to limb covering epithelium and the chondrogenic mesenchymal cell lineages. EGF immunostaining patterns suggested a paracrine type of regulation for the cartilage blastema associated with forelimb development. To test whether EGF effects the timing and positional information required for limb-specific cartilage morphogenesis, we employed tyrphostin (RG 50864) which inhibits EGF receptor kinase activity in a concentration-dependent manner and severely retards limb development. These findings support our hypothesis that endogenous EGF or EGF-like proteins provide signaling for the size and shape of discrete forelimb cartilage formations during mouse embryonic morphogenesis.

Animals↗
PubMed1993

Sister chromatid fusion initiates amplification of the dihydrofolate reductase gene in Chinese hamster cells.

We have utilized a dihydrofolate reductase (DHFR) probe in combination with selected probes from other positions along the 2q chromosome arm in a two-color fluorescence in situ hybridization analysis of early DHFR gene amplification events in CHO cells. These studies show clearly that the most frequent initiating event is the formation of a giant inverted duplication, resulting from chromosome breakage and terminal fusion or a reverse unequal sister chromatid exchange. The dicentric chromosomes thus formed initiate bridge/breakage/fusion cycles that appear to mediate subsequent amplification steps to higher copy number.

Animals↗
PubMed1993

An improved microassay for Plasmodium falciparum cytoadherence using stable transformants of Chinese hamster ovary cells expressing CD36 or intercellular adhesion molecule-1.

Stable transformants of Chinese hamster ovary (CHO) cell lines expressing high levels of human CD36 or intercellular adhesion molecule-1 (ICAM-1) have been produced as target cells for cytoadherence of Plasmodium falciparum-infected erythrocytes. An improved adherence microassay has been designed using small sample volumes and allowing convenient and reliable measurements on a large number of samples. The assay can be used both with purified proteins spotted on plastic and with the stably transformed CHO cell lines. The same assay plate can be evaluated either microscopically or by scintillation counting after use of 3H-hypoxanthine-labeled parasites. Using the microassay, functional expression of the transfected receptor molecules on CHO-CD36 and CHO-ICAM was confirmed using parasites with different cytoadherence phenotypes and cytoadherence inhibition experiments with a panel of anti-CD36 antibodies. The use of isolates from The Gambia confirmed the applicability of these assays for laboratory studies of these isolates.

Amino Acid Sequence↗
PubMed1993

[Study on lignans from Diphylleia sinensis].

A new lignan along with eight known lignans and a flavonoid were isolated from the rhizomes of Diphylleia sinensis Li.. Their structures were elucidated on the basis of chemical and spectral analysis. The new lignan, compound IX, was named as picropodophyllin-1-ethyl ether (IX). The eight known lignans were identified as podophyllotoxin (I), isopicropodophyllone (II), dehydropodophyllotoxin (III), diphyllin (IV), picropodophyllin (V), podophyllotoxone (VI), 4'-demethylpodophyllotoxin (VII) and picropodophyllin glucoside (VIII). Compounds II, VI, VII and VIII were found for the first time from the rhizome of this plant. The flavonoid was identified as kaempferol.

Antineoplastic Agents, Phytogenic↗
PubMed1993

Interdigital soft tissue separation induced by retinoic acid in mouse limbs cultured in vitro.

The temporal pattern of separation of the soft tissue between mouse digits was examined in an organ culture model system. Mouse limbs of different gestational age were cultured in vitro and the pattern of separation of the digits characterized. By gestational day 12.5 (E12.5) the limbs were committed to undergo separation of the soft tissue in the interdigital space when cultured in vitro. Prior to E12.5 digital separation did not occur and the limb tissues were not committed to this process. The addition of 10(-7) M retinoic acid (RA) to the media of E12 limbs was capable of inducing digit separation in the uncommitted limbs. Both the soft and hard tissue development of digits formed in vitro for either committed limbs or uncommitted limbs induced with RA was similar to the in vivo pattern.

Animals↗