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COONEY AUSTIN J.; KATZ DEBORAH; HUMMELKE GEOFFREY C.; JACKSON KATHY J. 《Integrative and comparative biology》1999,39(4):796-806
Germ Cell Nuclear Factor (GCNF) is an orphan member of the nuclearreceptor gene superfamily. Much has been understood about thefunctioning of GCNF which represents a candidate receptor fora novel hormonal signalling pathway. GCNF is not closely relatedto other members of the nuclear receptor superfamily and formsits own branch within the superfamily tree. It has a uniqueexpression pattern that spans both embryonic and adult stagesof development. In the adult, it is expressed in the germ cells:oocytes and spermatogenic cells as well as specific neuronalcells within the brain. In the embryo, GCNF expression is turnedon after gastrulation in all germ layers the ectoderm, mesodermand endoderm. An antero-posterior gradient of GCNF is establishedin the neuroectoderm of the embryo, suggesting a role in regulationof neuronal and germ cell development. Regulation of physiologicalprocesses by a nuclear receptor is achieved through regulationof gene expression. GCNF is the only nuclear receptor to specifcallybind to DR0 hormone response elements to regulate gene expression.In the absense of a ligand, GCNF represses gene expression.GCNF is capable of regulating the expression of the protaminegenes in a response element-dependent manner. At present theligand for GCNF is unknown, but it is hypothesized that GCNFis a receptor for a novel hormonal signalling pathway that effectsits biological response by regulating the expression of a subsetof genes containing DR0 response elements. 相似文献
3.
ROY T. CHURCHWELL CRAIG A. DAVIS SAMUEL D. FUHLENDORF DAVID M. ENGLE 《The Journal of wildlife management》2008,72(7):1596-1604
Abstract Grassland birds have declined more than any other North American habitat-associated bird community. Because most species of grassland birds evolved within heterogeneous landscapes created by the interaction of fire and grazing, traditional rangeland management that promotes homogeneity, including annual dormant-season burning combined with early-intensive grazing, might be partly responsible for these declines, especially in some regions of the Great Plains, USA. Recently, an alternative grassland management practice known as patch-burning has been promoted as a means of restoring heterogeneity to grasslands by mimicking the grazing-fire interaction that once occurred on the prairie before European settlement. From 2003 to 2004, we examined effects of patch-burning and traditional management (annual burning followed by early-intensive grazing) on the reproductive success of dickcissels (Spiza americana) in tallgrass prairie in Oklahoma. We monitored 296 dickcissel nests and found that dickcissel nesting phenology differed between traditional and patch-burned pastures. Specifically, dickcissels tended to initiate their nests later in the traditional pasture. Mean number of eggs laid and fledglings produced were similar between the treatments, but nest densities were higher in traditional pastures. Predation was the predominant cause of nest failure and was higher in traditional pastures than in patch-burned pastures. Brown-headed cowbird (Molothrus ater) parasitism was higher in traditional pastures than in patch-burned pastures. Overall, dickcissel nest success was higher in patch-burned pastures than in traditional pastures. The positive response of dickcissel nest success to patch-burn management provides further evidence that this practice can be a useful tool for grassland bird conservation. By creating a mosaic of different stature vegetation, patch-burn management enhances productivity of grassland bird species by providing a refuge area in the unburned patches that affords dickcissels and other nesting grassland birds some protection from the direct (e.g., trampling) and indirect (e.g., cowbird parasitism and predation) effects of grazing, which are not available under traditional management. Patch-burn management should be encouraged as a conservation strategy for grassland birds throughout the Great Plains. 相似文献
4.
Synthesis of Substance P 总被引:3,自引:0,他引:3
GEOFFREY W. TREGEAR HUGH D. NIALL JOHN T. POTTSJUN. SUSAN E. LEEMAN MICHAEL M. CHANG 《Nature: New biology》1971,232(29):87-89
SUBSTANCE P has been synthesized by the solid-phase procedure of Merrifield1,2 according to the sequence H-Arg-Pro-LysPro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2 reported in the previous letter. 相似文献
5.
Cell-free Studies on the Regulation of the Arabinose Operon 总被引:17,自引:0,他引:17
A DNA directed, cell-free system which synthesized L-ribulokinase coded by the L-arabinose operon ara OIBAD, has been developed. L-arabinose but not the araC gene product is required for the expression of this operon and, in addition, cyclic AMP and guanosine tetraphosphate are needed for optimal synthesis. 相似文献
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SAMUEL P.S. SVENSSON PER I. ADOLFSSON NILS GRUNDSTR
M JAN OLOF G. KARLSSON 《Pigment cell & melanoma research》1997,10(6):395-400
It has previously been shown that α2-adrenoceptors (α2-ARs) mediate pigment granule (melanosome) aggregation in melanophores of the teleost fish Labrus ossifagus. The present investigation scrutinized the signalling mechanisms of melanosome aggregation induced by sympathetic nerve stimulation or by exogenous addition of α-AR agonists and cAMP analogues. The following was observed: i) nerve-induced melanosome aggregation was associated with a rapid decrease in the cAMP level; ii) noradrenaline or medetomidine (an α2-AR agonist) caused melanosome aggregation and reduced the cAMP content; iii) RP-S-CI-cAMP, a membrane-permeating inhibitor of protein kinase A induced melanosome aggregation; and iv) B-HT 920 (an α2-AR agonist) and methoxamine (an α1-AR agonist) induced melanosome aggregation, although they did not reduce cAMP. It has been suggested that in some teleost species α1-ARs mediate melanosome aggregation by increasing the level of intracellular calcium. However, we found that the effect of methoxamine in melanophores from Labrus ossifagus could be blocked by yohimbine (an α2-AR antagonist) but not by equimolar concentration of prazosin (an α1-AR antagonist). Furthermore, 1 μM ionomycin (a calcium ionophore) did not induce melanosome aggregation. Our findings therefore do not indicate that α1-ARs and/or an increase in intracellular calcium mediate melanosome aggregation in Labrus ossifagus. Our results suggest that α2-AR-mediated melanosome aggregation is induced by multiple signalling pathways. One of these involves a reduction in cAMP, but none involves an increase in intracellular calcium. 相似文献
8.
An increase in the superoxide dismutase (SOD) activity inStreptococcus lactis was observed when the cells were grown at increased oxygen partial pressures or exposed to hyperbaric oxygen tensions. The NADH-oxidase/NADH-peroxidase activities inS. lactis increased in galactose-grown cells when cultivated in air compared with N2/CO2. This effect did not occur when glucose was the carbon source; however, an increase in the activities of these enzymes was observed in oxygen atmosphere. The correlation between SOD, NADH-oxidase/NADH-peroxidase, and the metabolic pathways involved is discussed. The effect of manganese on the SOD activity is also considered. 相似文献
9.
The cladistic relationships of Archaeopteryx , the earliest known bird, are re-examined and previous hypotheses of relationships evaluated. The morphology of Archaeopteryx is redescribed. New interpretations of the fossils are presented, particularly in regard to the morphology of the pectoral girdle, manus, pelvic girdle, tarsus and pes. These new interpretations challenge some of the phylogenetic hypotheses recently presented and a new version of thecodontian relationships is suggested. 相似文献
10.
HANS‐PETER SCHULTZE DIRK FUCHS SAMUEL GIERSCH CHRISTINA IFRIM WOLFGANG STINNESBECK 《Palaeontology》2010,53(3):689-694
Abstract: The supposed vestige of a cephalopod gladius from Turonian platy limestones at Vallecillo, north‐east Mexico, named Palaeoctopus pelagicus by Fuchs et al. in 2008, is reinterpreted and shown to be a gular plate of a coelacanth fish, possibly of the genus Megacoelacanthus. In addition to the gular plate, two extrascapulars and fin rays of all fins are preserved on one slab and its counterpart. This is the first record of a coelacanth from these lower Turonian strata at Vallecillo, which are rich in fish. 相似文献