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Biomedical subjects

M Megias

Publications and source records attributed to M Megias.

7 recordsLinked to original sources
PubMed2004

Chronic treatment with a precursor of cellular phosphatidylcholine ameliorates morphological and behavioral effects of aging in the mouse [correction of rat] hippocampus.

Normal aging is commonly associated with a decline in memory, mainly for that related with newly acquired information. The hippocampal formation (HF) is a brain region that has been implicated in this dysfunction. Within the HF there are several cellular types, such as pyramidal cells, granule neurons of the dentate gyrus, and astrocytes. CDP-choline is a well-known intermediate in the biosynthesis of phosphatidylcholine, a phospholipid essential for neuronal membrane preservation and function; thus, this compound would attenuate the process of neuronal aging. To test this, three groups of male mice were used in this study. An adult 12-month-old group (ACG), a 24-month-old (OCG), and an old experimental group (OEG) were administered orally a solution of CDP-choline (150 mg/kg per day) from 12 up to 24 months. Experimental observations suggest that CDP-choline has a positive effect on memory (reference errors were attenuated), and hippocampal morphology resembled that of younger animals.

Aging↗
PubMed1999

Mutation in GDP-fucose synthesis genes of Sinorhizobium fredii alters Nod factors and significantly decreases competitiveness to nodulate soybeans.

We mutagenized Sinorhizobium fredii HH103-1 with Tn5-B20 and screened about 2,000 colonies for increased beta-galactosidase activity in the presence of the flavonoid naringenin. One mutant, designated SVQ287, produces lipochitooligosaccharide Nod factors (LCOs) that differ from those of the parental strain. The nonreducing N-acetylglucosamine residues of all of the LCOs of mutant SVQ287 lack fucose and 2-O-methylfucose substituents. In addition, SVQ287 synthesizes an LCO with an unusually long, C20:1 fatty acyl side chain. The transposon insertion of mutant SVQ287 lies within a 1.1-kb HindIII fragment. This and an adjacent 2.4-kb HindIII fragment were sequenced. The sequence contains the 3' end of noeK, nodZ, and noeL (the gene interrupted by Tn5-B20), and the 5' end of nolK, all in the same orientation. Although each of these genes has a similarly oriented counterpart on the symbiosis plasmid of the broad-host-range Rhizobium sp. strain NGR234, there are significant differences in the noeK/nodZ intergenic region. Based on amino acid sequence homology, noeL encodes GDP-D-mannose dehydratase, an enzyme involved in the synthesis of GDP-L-fucose, and nolK encodes a NAD-dependent nucleotide sugar epimerase/dehydrogenase. We show that expression of the noeL gene is under the control of NodD1 in S. fredii and is most probably mediated by the nod box that precedes nodZ. Transposon insertion into neoL has two impacts on symbiosis with Williams soybean: nodulation rate is reduced slightly and competitiveness for nodulation is decreased significantly. Mutant SVQ287 retains its ability to form nitrogen-fixing nodules on other legumes, but final nodule number is attenuated on Cajanus cajan.

Amino Acid Sequence↗
PubMed1997

Differences between the circadian system of two strains of senescence-accelerated mice (SAM).

The aim of this study was to look for morphological or functional differences between the circadian system of two substrains of Senescence Accelerated Mice (SAM): senescence-prone (SAMP8; average median survival time = 10.0 months) and senescence-resistant (SAMR1; average median survival time = 18.9 months). Neither the general structure nor the quantitative analysis of the number of VP-positive neurons in matched sections revealed differences between SAMP8 and SAMR1 mice. Under LD 12/12 photoperiod, all animals showed the typical pattern of wheel running activity with maximum activity in the first half of darkness period. The period of the locomotor activity in free running as well as the time course for synchronization after a 6 h phase delay of LD cycle were similar in both strains of SAM mice. However, SAMP8 animals reentrained significantly earlier (3.4 +/- 0.4 days) than SAMR1 (6.3 +/- 0.9 days) after a 6 h phase advance of LD cycle. We conclude that the circadian system of SAMP8 mice presents some functional differences with that of SAMR1, which could help to explain their different rate of ageing.

Aging↗
PubMed1990

Structure of the extracellular polysaccharide secreted by Rhizobium leguminosarum var. phaseoli CIAT 899.

The structure of the extracellular polysaccharide secreted by Rhizobium leguminosarum var. phaseoli CIAT 899 has been studied by methylation analysis. 1H-n.m.r. spectroscopy, and partial acid hydrolysis. The repeating unit is an octasaccharide made up of D-glucose, D-galactose, pyruvic acid, and acetic acid in the molar ratios 6:2:1.5:1.5. Half of the terminal Gal groups are 4,6-substituted by pyruvic acid acetal groups and the other half by O-acetyl groups at position 3. Also, one of the 3-linked glucosyl residues carries a pyruvic acid 4,6-acetal group and one of the 4-linked glucosyl residues is acetylated at position 6.

Carbohydrate Sequence↗
PubMed1990

Identification and cloning of nodulation genes and host specificity determinants of the broad host-range Rhizobium leguminosarum biovar phaseoli strain CIAT899.

Rhizobium leguminosarum biovar phaseoli type II strain CIAT899 nodulates a wide range of hosts: Phaseolus vulgaris (beans), Leucaena esculenta (leucaena) and Macroptilium atropurpureum (siratro). A nodulation region from the symbiotic plasmid has been isolated and characterized. This region, which is contained in the overlapping cosmid clones pCV38 and pCV117, is able to induce nodules in beans, leucaena and siratro roots when introduced in strains cured for the symbiotic plasmid, pSym. In addition, this cloned region extends the host range of Rhizobium meliloti and R. leguminosarum biovar (bv.) trifolii wild-type strains to nodulate beans. Analysis of constructed subclones indicates that a 6.4kb HindIII fragment contains the essential genes required for nodule induction on all three hosts. Rhizobium leguminosarum bv. phaseoli type I strain CE3 nodulates only beans. However, CE3 transconjugants harbouring plasmid pCV3802 (which hybridized to a nodD heterologous probe), were capable of eliciting nodules on leucaena and siratro roots. Our results suggest that the CIAT899 DNA region hybridizing with the R. meliloti nodD detector is involved in the extension of host specificity to promote nodule formation in P. vulgaris, L. esculenta and M. atropurpureum.

Cloning, Molecular↗