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41.
Sea urchin Hox genes: insights into the ancestral Hox cluster 总被引:3,自引:0,他引:3
We describe the Hox cluster in the radially symmetric sea urchin and
compare our findings to what is known from clusters in bilaterally
symmetric animals. Several Hox genes from the direct-developing sea urchin
Heliocidaris erythrogramma are described. CHEF gel analysis shows that the
Hox genes are clustered on a < or = 300 kilobase (kb) fragment of DNA,
and only a single cluster is present, as in lower chordates and other
nonvertebrate metazoans. Phylogenetic analyses of sea urchin, amphioxus,
Drosophila, and selected vertebrate Hox genes confirm that the H.
erythrogramma genes, and others previously cloned from other sea urchins,
belong to anterior, central, and posterior groups. Despite their radial
body plan and lack of cephalization, echinoderms retain at least one of the
anterior group Hox genes, an orthologue of Hox3. The structure of the
echinoderm Hox cluster suggests that the ancestral deuterostome had a Hox
cluster more similar to the current chordate cluster than was expected Sea
urchins have at least three Abd-B type genes, suggesting that Abd-B
expansion began before the radiation of deuterostomes.
相似文献
42.
Kainic acid-induced seizures: changes in brain extracellular ions as assessed by intracranial microdialysis 总被引:1,自引:0,他引:1
The effect of kainic acid on extracellular [K+], [Ca2+], and [Na+] in the rat piriform cortex and hippocampus was studied by means of intracranial microdialysis. Either a dialysis fiber loop or horizontal Vita fiber were stereotaxically implanted within the piriform cortex or hippocampus, respectively. About 24 h later, fibers were perfused (1 ml/min) with Krebs-Ringer bicarbonate solution. Effluent samples were collected before (four at 30 min intervals), and after (six at 30 min intervals) administration of kainic acid (16 mg/kg, i.p.) or kainic acid vehicle. Kainic acid induced sequential signs of lethargy, staring, "wet-dog shakes," forepaw clonus, and tonic-clonic convulsions. In these awake free-moving rats, kainic acid induced a rapid and prolonged increase in extracellular [K+] and an apparent, but not statistically significant, decrease in extracellular [Ca2+] within the hippocampus. In the piriform cortex, kainic acid induced increases in extracellular [K+] and [Na+], which were associated with early pre-convulsive signs. In contrast to the pronounced ion changes commonly seen when the brain is activated by factors such as local application of excitatory substances or when the brain is made ischemic or hypoxic, extracellular ion concentrations are relatively well maintained during parenteral kainic acid-induced seizures. 相似文献
43.
The assimilation of 14CO2 into the C4 acids malate and aspartate by leaves of C3, C4 and C3–C4 intermediate Flaveria species was investigated near the CO2 compensation concentration * in order to determine the potential role of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) in reducing photorespiration in the intermediates. Relative to air concentrations of CO2, the proportion of CO2 fixed by PEP carboxylase at * increased in all six C3–C4 intermediate species examined. However, F. floridana J.R. Johnston and F. ramosissima Klatt were shown to be markedly less responsive to reduced external CO2, with only about a 1.6-fold enhancement of CO2 assimilation by PEP carboxylase, as compared to a 3.0- to 3.7-fold increase for the other C3–C4 species examined, namely, F. linearis Lag., F. anomala B.L. Robinson, F. chloraefolia A. Gray and F. pubescens Rydb. The C3 species F. pringlei Gandoger and F. cronquistii A.M. Powell exhibited a 1.5- and 2.9-fold increase in labeled malate and aspartate, respectively, at *. Assimilation of CO2 by PEP carboxylase in the C4 species F. trinervia (Spreng.) C. Mohr, F. australasica Hook., and the C4-like species F. brownii A.M. Powell was relatively insensitive to subatmospheric levels of CO2. The interspecific variation among the intermediate Flaverias may signify that F. floridana and F. ramosissima possess a more C4-like compartmentation of PEP carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) between the mesophyll and bundle-sheath cells. Chasing recently labeled malate and aspartate with 12CO2 for 5 min at * resulted in an apparent turnover of 25% and 30% of the radiocarbon in these C4 acids for F. ramosissima and F. floridana, respectively. No substantial turnover was detected for F. linearis, F. anomala, F. chloraefolia or F. pubescens. With the exception of F. floridana and F. ramosissima, it is unlikely that enhanced CO2 fixation by PEP carboxylase at the CO2 compensation concentration is a major mechanism for reducing photorespiration in the intermediate Flaveria species. Moreover, these findings support previous related 14CO2-labeling studies at air-levels of CO2 which indicated that F. floridana and F. ramosissima were more C4-like intermediate species. This is further substantiated by the demonstration that F. floridana PEP carboxylase, like the enzyme in C4 plants, undergoes a substantial activation (2.2-fold) upon illuminating dark-adapted green leaves. In contrast, light activation was not observed for the enzyme in F. linearis or F. chloraefolia.Abbreviations and symbols PEP
phosphoenolpyruvate
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
-
CO2 compensation concentration
- *
a subatmospheric level of CO2 approximating
Published as Paper No. 8832, Journal Series, Nebraska Agricultural Research Division 相似文献
44.
45.
Tripropyltin restores medium acidification by washed corn root tissue in which electrogenic H+ efflux has been blocked by ATPase inhibitors or injury. However, the restored H+ efflux is not electrogenic and will not drive K+ influx, and, by itself, tripropyltin is inhibitory to K+ influx. Tripropyltin elicits a 5-fold increase in endogenous chloride efflux, and Cl−/OH− exchange can, thus, account for the observed acidification of the medium. This explanation cannot be applied equally to the acidification produced by the K+/H+ exchanging ionophore nigericin. 相似文献
46.
Synthesis and purification of large amounts of RNA oligonucleotides. 总被引:31,自引:0,他引:31
47.
The didelphid marsupial, Didelphis aurita, is suggested as an intraguild predator and as key‐species in small mammal assemblages of the Atlantic Forest of Brazil. The field experiments required to test this hypothesis are complex to implement, but the recent revival of regression methods offers a viable alternative. Here we use the dynamic and static regression methods to determine the importance of D. aurita as a competitor and intraguild predator. Capture–recapture data from two localities in the Rio de Janeiro State were used, Garrafão (municipality of Guapimirim), a coastal forest of the Serra do Mar, and Barra de Maricá, a costal sand dune vegetation. Population and microhabitat variables were monitored from April 1997 to April 2003 in Garrafão, and from January 1986 to July 1990 in Barra de Maricá. Microhabitat variables were related to Canopy, Plant, Litter and Rock covers, Obstruction from 0 to 1.5 m, and Number of logs. Exploitation competition was tested by the dynamic method, which models the effects of D. aurita on the per capita growth rate of a species. Interference by predation or competition was tested by the static method, where the abundance of D. aurita at trap stations was regressed against the abundance of other small mammals, after removal of any variation associated with microhabitat factors. Exploitation competition was not detected, but the interference of D. aurita was pervasive, affecting all small mammals studied in the two localities. The clear avoidance of D. aurita by all small mammals tested in two localities of different physiognomies indicates that it functions as an intraguild predator, even if actual predation by D. aurita is an occasional event. 相似文献
48.
We are currently in an interesting phase of plant biotechnology releases, both for the scientists responsible for these innovations who are beginning to see their ideas realized, and for the biotechnology companies that are starting to see a return on their investment. One of the most notable examples, is the introduction of transgenic crops that are engineered to express a Bacillus thuringiensis toxin that confers resistance to insect predation. However, the picture is not altogether positive - there is concern that the introduction of this technology was premature or should not have happened at all, and that the valuable insecticidal properties of Bacillus thuringiensis will be lost. 相似文献
49.
Comparative immunogenicity in rhesus monkeys of DNA plasmid,recombinant vaccinia virus,and replication-defective adenovirus vectors expressing a human immunodeficiency virus type 1 gag gene 总被引:9,自引:0,他引:9 下载免费PDF全文
Casimiro DR Chen L Fu TM Evans RK Caulfield MJ Davies ME Tang A Chen M Huang L Harris V Freed DC Wilson KA Dubey S Zhu DM Nawrocki D Mach H Troutman R Isopi L Williams D Hurni W Xu Z Smith JG Wang S Liu X Guan L Long R Trigona W Heidecker GJ Perry HC Persaud N Toner TJ Su Q Liang X Youil R Chastain M Bett AJ Volkin DB Emini EA Shiver JW 《Journal of virology》2003,77(11):6305-6313
Cellular immune responses, particularly those associated with CD3+ CD8+ cytotoxic T lymphocytes (CTL), play a primary role in controlling viral infection, including persistent infection with human immunodeficiency virus type 1 (HIV-1). Accordingly, recent HIV-1 vaccine research efforts have focused on establishing the optimal means of eliciting such antiviral CTL immune responses. We evaluated several DNA vaccine formulations, a modified vaccinia virus Ankara vector, and a replication-defective adenovirus serotype 5 (Ad5) vector, each expressing the same codon-optimized HIV-1 gag gene for immunogenicity in rhesus monkeys. The DNA vaccines were formulated with and without one of two chemical adjuvants (aluminum phosphate and CRL1005). The Ad5-gag vector was the most effective in eliciting anti-Gag CTL. The vaccine produced both CD4+ and CD8+ T-cell responses, with the latter consistently being the dominant component. To determine the effect of existing antiadenovirus immunity on Ad5-gag-induced immune responses, monkeys were exposed to adenovirus subtype 5 that did not encode antigen prior to immunization with Ad5-gag. The resulting anti-Gag T-cell responses were attenuated but not abolished. Regimens that involved priming with different DNA vaccine formulations followed by boosting with the adenovirus vector were also compared. Of the formulations tested, the DNA-CRL1005 vaccine primed T-cell responses most effectively and provided the best overall immune responses after boosting with Ad5-gag. These results are suggestive of an immunization strategy for humans that are centered on use of the adenovirus vector and in which existing adenovirus immunity may be overcome by combined immunization with adjuvanted DNA and adenovirus vector boosting. 相似文献
50.
Chastain PD Makhov AM Nossal NG Griffith J 《The Journal of biological chemistry》2003,278(23):21276-21285
Rolling circle replication has previously been reconstituted in vitro using M13 duplex circles containing preformed forks and the 10 purified T4 bacteriophage replication proteins. Leading and lagging strand synthesis in these reactions is coupled and the size of the Okazaki fragments produced is typical of those generated in T4 infections. In this study the structure of the DNAs and DNA-protein complexes engaged in these in vitro reactions has been examined by electron microscopy. Following deproteinization, circular duplex templates with linear tails as great as 100 kb are observed. The tails are fully duplex except for one to three single-stranded DNA segments close to the fork. This pattern reflects Okazaki fragments stopped at different stages in their synthesis. Examination of the DNA-protein complexes in these reactions reveals M13 duplex circles in which 64% contain a single large protein mass (replication complex) and a linear duplex tail. In 56% of the replicating molecules with a tail there is at least one fully duplex loop at the replication complex resulting from the portion of the lagging strand engaged in Okazaki fragment synthesis folding back to the replisome. The single-stranded DNA segments at the fork bound by gene 32 and 59 proteins are not extended but rather appear organized into highly compact structures ("bobbins"). These bobbins constitute a major portion of the mass of the full replication complex. 相似文献