Discovery of natural atypical nonhemolytic Listeria seeligeri isolates

We found seven Listeria isolates, initially identified as isolates with the Xyl(+) Rha(-) biotype of Listeria welshimeri by phenotypic tests, which exhibited discrepant genotypic properties in a well-validated Listeria species identification oligonucleotide microarray. The microarray gives results of these seven isolates being atypical hly-negative L. seeligeri isolates, not L. welshimeri isolates. The aberrant L. seeligeri isolates were d-xylose fermentation positive, l-rhamnose fermentation negative (Xyl(+) Rha(-)), and nonhemolytic on blood agar and in the CAMP test with both Staphylococcus aureus (S(-) reaction) and Rhodococcus equi (R(-) reaction). All genes of the prfA cluster of L. seeligeri, located in the prs-ldh region, including the orfA2, orfD, prfA, orfE, plcA, hly, orfK, mpl, actA, dplcB, plcB, orfH, orfX, orfI, orfP, orfB, and orfA genes, were checked by PCR and direct sequencing for evidence of their presence in the atypical isolates. The prs-prfA cluster-ldh region of the L. seeligeri isolates was approximately threefold shorter due to the loss of orfD, prfA, orfE, plcA, hly, orfK, mpl, actA, dplcB, plcB, orfH, orfX, and orfI. The genetic map order of the cluster genes of all the atypical L. seeligeri isolates was prs-orfA2-orfP-orfB-orfA-ldh, which was comparable to the similar region in L. welshimeri, with the exception of the presence of orfA2. DNA sequencing and phylogenetic analysis of 17 housekeeping genes indicated an L. seeligeri genomic background in all seven of the atypical hly-negative L. seeligeri isolates. Thus, the novel biotype of Xyl(+) Rha(-) Hly(-) L. seeligeri strains can only be distinguished from Xyl(+) Rha(-) L. welshimeri strains genotypically, not phenotypically. In contrast, the Rha(+) Xyl(+) biotype of L. welshimeri would not present an identification issue.     

Genomic imprinting in fetal growth and development

Each somatic cell of the human body contains 46 chromosomes consisting of two sets of 23; one inherited from each parent. These chromosomes can be categorised as 22 pairs of autosomes and two sex chromosomes; females are XX and males are XY. Similarly, at the molecular level, two copies of each autosomal gene exist; one copy derived from each parent. Until the mid-1980s, it was assumed that each copy of an autosome or gene was functionally equivalent, irrespective of which parent it was derived from. However, it is now clear from classical experiments in mice and from examples of human genetic disease that this is not the case. The functional activity of some genes or chromosomal regions is unequal, and dependent on whether they have been inherited maternally or paternally. This phenomenon is termed 'genomic imprinting' and the activity or silence of an imprinted gene or chromosomal region is set during gametogenesis. Genomic imprinting involving the autosomes appears to be restricted to eutherian mammals, and has most likely evolved as a result of the conflicting concerns of the parental genomes in the growth and development of their offspring. When the normal pattern of imprinting is disrupted, the phenotypes observed in humans and mice are generally associated with abnormal fetal growth, development and behaviour, illustrating its importance for a normal intrauterine environment. The characteristics of imprinted genes, their regulation and the phenotypes associated with altered imprinting are discussed.     

Acute lesions of the ventromedial hypothalamus reduce sympathetic activation and thermogenic changes induced by PGE1

The aim of this experiment was to evaluate the effects of an intracerebroventricular (icv) injection of prostaglandin E1 (PGE₁) on the sympathetic activation and the thermogenic changes in rats with acute lesions of the ventromedial hypothalamus (VMH). Four groups of six Sprague-Dawley male rats were anesthetized with ethyl-urethane. The firing rate of the sympathetic nerves innervating the interscapular brown adipose tissue (IBAT) and the colonic and IBAT temperatures were monitored both before and after one of the following treatments: 1) VMH lesion plus icv injection of PGE₁ (500 ng); 2) VMH lesion plus icv injection of saline; 3) sham lesion plus icv injection of PGE₁; and 4) sham lesion plus icv injection of saline. PGE₁ induced an increase in the firing rate of IBAT nerves and the colonic and IBAT temperatures. These effects were reduced by VMH lesion. The findings indicate that acute lesions of the VMH reduce the effects of PGE₁ and seem to suggest a possible role played by the VMH in the control of the sympathetic activation and the thermogenic changes during PGE₁ hyperthermia.     

Population structure in the American oyster as inferred by nuclear gene genealogies

Multiple haplotypes from each of three nuclear loci were isolated and sequenced from geographic populations of the American oyster, Crassostrea virginica. In tests of alternative phylogeographic hypotheses for this species, nuclear gene genealogies constructed for these haplotypes were compared to one another, to a mitochondrial gene tree, and to patterns of allele frequency variation in nuclear restriction site polymorphisms (RFLPs) and allozymes. Oyster populations from the Atlantic versus the Gulf of Mexico are not reciprocally monophyletic in any of the nuclear gene trees, despite considerable genetic variation and despite large allele frequency differences previously reported in several other genetic assays. If these populations were separated vicariantly in the past, either insufficient time has elapsed for neutral lineage sorting to have achieved monophyly at most nuclear loci, or balancing selection may have inhibited lineage extinction, or secondary gene flow may have moved haplotypes between regions. These and other possibilities are examined in light of available genetic evidence, and it is concluded that no simple explanation can account for the great variety of population genetic patterns across loci displayed by American oysters. Regardless of the source of this heterogeneity, this study provides an empirical demonstration that different sequences of DNA within the same organismal pedigree can have quite different phylogeographic histories.      

植物抗病基因工程进展(续)

植物抗病基因工程进展（续）洪剑明印莉萍邱泽生（首都师范大学生物系北京１０００３７）ＰＲＯＧＲＥＳＳＯＦＧＥＮＥＴＩＣＥＮＧＩＮＥＥＲＩＮＧＦＯＲＰＬＡＮＴＤＩＳＥＡＳＥＲＥＳＩＳＴＡＮＣＥＨＯＮＧＪｉａｎＭｉｎｇＹＩＮＬｉＰｉｎｇＱＩＵＺｅＳｈ...     

Comparative macromolecular composition of filaments and rods of a Bacillus megaterium thermoconditional morphological mutant.

Filaments of a thermosensitive Bacillus megaterium mutant showed an altered macromolecular composition compared with salt-cured mutant cells and parental cells. Filaments contained more peptidoglycan, polyglucose, poly-beta-hydroxy-butyrate, and deoxyribonucleic acid per unit of protein. The ribonucleic acid-to-protein ratio of filaments was similar to that of rods or salt-cured cells. Filament formation seemed to be due to defective protein or ribonucleic acid metabolism.     

Estrogen synthesis and metabolism in the hamster blastocyst, uterus and liver near the time of implantation

The steroidogenic potential of hamster tissues, just prior to implantation of the blastocyst in the uterus, was characterized by incubating blastocysts (14) and pieces of endometrium with [1, 2-3H]-androstenedione for 24 h. [3H]-2-Methoxyestradiol was synthesized, but intermediate estrogens were not found. To obtain a more quantitative assessment and comparison of steroidogenic activity, especially aromatase activity, in these tissues as well as in the uterine myometrium and liver and to increase the possibility of recovering estradiol, microsomes were isolated from 244 blastocysts and portions of the other tissues. Microsomes were incubated with [1 alpha, 2 alpha-3H]-testosterone plus [1 beta,2 beta-3H]-testosterone for 6 h. During this time [3H]-metabolites were synthesized by all tissues as indicated by HPLC. [3H]-Androstenedione was noted and values were higher than control levels (medium alone or microsomes from uterine flush fluid) in all samples but liver. [3H]-Estradiol was detected at an elevated level only in the blastocyst sample; however, addition of unlabeled estradiol during the subsequent incubation of endometrial, myometrial and liver microsomes increased the recovery of [3H]-estradiol. Identities of [3H]-2-methoxyestradiol from the first experiment and [3H]-androstenedione and [3H]-estradiol from the second experiment were confirmed by recrystallization. The formation of 3H2O from [beta-3H]-testosterone was used as an index of aromatase activity. After subtracting control medium values, blastocysts were 24-fold more active (dpm/microgram protein) than the endometrium and myometrium in synthesizing 3H2O. While there was no difference in synthetic potential between endometrium and myometrium, aromatase activity in these tissues was greater than that of the liver. Microsomes from uterine flush fluid displayed no capacity for synthesizing 3H2O indicating that the elevated blastocyst levels were not caused by contaminating endometrial cells. These results indicate that all of the tissues examined have the capacity to metabolize C19-steroids to a variety of hormones, including estrogens, and further, that estrogen metabolism occurs rapidly in these tissues. This capacity may be important for providing a suitable hormonal milieu at the time of implantation.     

Specificity and control of uptake of purines and other compounds in Bacillus subtilis.

Certain nucleotides control adaptation to changing nutrition or differentiation (sporulation) resulting from a general nutritional deficiency. To maintain the adaptation or differentiation process, once it has started, it may have been important for cells to evolve several independent and metabolically controllable systems enabling the uptake and metabolism of various nucleic acid bases or nucleosides. We have analyzed the cellular reactions with these compounds by measuring both their effect on growth and their uptake in appropriately chosen auxotrophic and uptake mutants. We have found one uptake system for guanine and hypoxanthine, another one for guanosine and inosine, and three other systems for adenine, adenosine, and uracil. The uptake systems of guanine-hypoxanthine and guanosine-inosine are inhibited by the stringent response to amino acid deprivation (increase of guanosine 5'-diphosphate-3'-diphosphate), but they do not depend on the concentration of GTP, which decreases during sporulation. In contrast, the uptake of Ura depends on the presence of GTP, regardless of whether a GTP decrease was produced by the stringent response or otherwise. This was the only uptake system whose decrease was always correlated with the onset of sporulation. The uptake of other compounds, e.g., alpha-methylglucoside and alpha-aminoisobutyric acid, decreased under some, but not all, sporulation conditions.     

Evolution of arthropod hemocyanins and insect storage proteins (hexamerins)

Crustacean and cheliceratan hemocyanins (oxygen-transport proteins) and insect hexamerins (storage proteins) are homologous gene products, although the latter do not bind oxygen and do not possess the copper- binding histidines present in the hemocyanins. An alignment of 19 amino acid sequences of hemocyanin subunits and insect hexamerins was made, based on the conservation of elements of secondary structure observed in X-ray structures of two hemocyanin subunits. The alignment was analyzed using parsimony and neighbor-joining methods. Results provide strong indications for grouping together the sequences of the 2 crustacean hemocyanin subunits, the 5 cheliceratan hemocyanin subunits, and the 12 insect hexamerins. Within the insect clade, four methionine- rich proteins, four arylphorins, and two juvenile hormone-suppressible proteins from Lepidoptera, as well as two dipteran proteins, form four separate groups. In the absence of an outgroup sequence, it is not possible to present information about the ancestral state from which these proteins are derived. Although this family of proteins clearly consists of homologous gene products, there remain striking differences in gene organization and site of biosynthesis of the proteins within the cell. Because studies on 18S and 12S rRNA sequences indicate a rather close relationship between insects and crustaceans, we propose that hemocyanin is the ancestral arthropod protein and that insect hexamerins lost their copper-binding capability after divergence of the insects from the crustaceans.