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61.
Neural induction and regionalisation in the chick embryo. 总被引:3,自引:0,他引:3
K G Storey J M Crossley E M De Robertis W E Norris C D Stern 《Development (Cambridge, England)》1992,114(3):729-741
Induction and regionalisation of the chick nervous system were investigated by transplanting Hensen's node into the extra-embryonic region (area opaca margin) of a host embryo. Chick/quail chimaeras were used to determine the contributions of host and donor tissue to the supernumerary axis, and three molecular markers, Engrailed, neurofilaments (antibody 3A10) and XlHbox1/Hox3.3 were used to aid the identification of particular regions of the ectopic axis. We find that the age of the node determines the regions of the nervous system that form: young nodes (stages 2-4) induced both anterior and posterior nervous system, while older nodes (stages 5-6) have reduced inducing ability and generate only posterior nervous system. By varying the age of the host embryo, we show that the competence of the epiblast to respond to neural induction declines after stage 4. We conclude that during normal development, the initial steps of neural induction take place before stage 4 and that anteroposterior regionalisation of the nervous system may be a later process, perhaps associated with the differentiating notochord. We also speculate that the mechanisms responsible for induction of head CNS differ from those that generate the spinal cord: the trunk CNS could arise by homeogenetic induction by anterior CNS or by elongation of neural primordia that are induced very early. 相似文献
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Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
65.
Genetic dissection of carotenoid synthesis in arabidopsis defines plastoquinone as an essential component of phytoene desaturation. 总被引:11,自引:0,他引:11 下载免费PDF全文
Carotenoids are C40 tetraterpenoids synthesized by nuclear-encoded multienzyme complexes located in the plastids of higher plants. To understand further the components and mechanisms involved in carotenoid synthesis, we screened Arabidopsis for mutations that disrupt this pathway and cause accumulation of biosynthetic intermediates. Here, we report the identification and characterization of two nonallelic albino mutations, pds1 and pds2 (for phytoene desaturation), that are disrupted in phytoene desaturation and as a result accumulate phytoene, the first C40 compound of the pathway. Surprisingly, neither mutation maps to the locus encoding the phytoene desaturase enzyme, indicating that the products of at least three loci are required for phytoene desaturation in higher plants. Because phytoene desaturase catalyzes an oxidation reaction, it has been suggested that components of an electron transport chain may be involved in this reaction. Analysis of pds1 and pds2 shows that both mutants are plastoquinone and tocopherol deficient, in addition to their inability to desaturate phytoene. Separate steps of the plastoquinone/tocopherol biosynthetic pathway are affected by these two mutations. The pds1 mutation affects the enzyme 4-hydroxyphenylpyruvate dioxygenase because it can be rescued by growth on the product but not the substrate of this enzyme, homogentisic acid and 4-hydroxyphenylpyruvate, respectively. The pds2 mutation most likely affects the prenyl/phytyl transferase enzyme of this pathway. Because tocopherol-deficient mutants in the green alga Scenedesmus obliquus can synthesize carotenoids, our findings demonstrate conclusively that plastoquinone is an essential component in carotenoid synthesis. We propose a model for carotenoid synthesis in photosynthetic tissue whereby plastoquinone acts as an intermediate electron carrier between carotenoid desaturases and the photosynthetic electron transport chain. 相似文献
66.
Summary This review provides an update on the variety of histochemical techniques available for the cellular localization and expression
of nitric oxide synthase in formalin-fixed tissue sections. The techniques of immunohistochemistry and NADPH-diaphorase histochemistry
are discussed and the suitability of various types of probes and reporters which are useful forin situ detection of nitric oxide synthase mRNA expression are assessed. Figures are also included which illustrate the techniques
described and protocols forin situ hybridization and NADPH-diaphorase histochemistry. 相似文献
67.
Physical map of the genome of Treponema pallidum subsp. pallidum (Nichols). 总被引:3,自引:2,他引:1 下载免费PDF全文
E M Walker J K Howell Y You A R Hoffmaster J D Heath G M Weinstock S J Norris 《Journal of bacteriology》1995,177(7):1797-1804
A physical map of the chromosome of Treponema pallidum subsp. pallidum (Nichols), the causative agent of syphilis, was constructed from restriction fragments produced by NotI, SfiI, and SrfI. These rare-cutting restriction endonucleases cleaved the T. pallidum genome into 16, 8, and 15 fragments, respectively. Summation of the physical lengths of the fragments indicates that the chromosome of T. pallidum subsp. pallidum is approximately 1,030 to 1,080 kbp in size. The physical map was constructed by hybridizing a variety of probes to Southern blots of single and double digests of T. pallidum genomic DNA separated by contour-clamped homogeneous electric field electrophoresis. Probes included cosmid clones constructed from T. pallidum subsp. pallidum genomic DNA, restriction fragments excised from gels, and selected genes. Physical mapping confirmed that the chromosome of T. pallidum subsp. pallidum is circular, as the SfiI and SrfI maps formed complete circles. A total of 13 genes, including those encoding five membrane lipoproteins (tpn47, tpn41, tpn29-35, tpn17, and tpn15), a putative outer membrane porin (tpn50), the flagellar sheath and hook proteins (flaA and flgE), the cytoplasmic filament protein (cfpA), 16S rRNA (rrnA), a major sigma factor (rpoD), and a homolog of cysteinyl-tRNA synthetase (cysS), have been localized in the physical map as a first step toward studying the genetic organization of this noncultivable pathogen. 相似文献
68.
Identification of a protein that binds to the Ho endonuclease recognition sequence at the yeast mating type locus. 总被引:2,自引:0,他引:2 下载免费PDF全文
Mating type switching in Saccharomyces cerevisiae initiates when Ho endonuclease makes a site-specific double-stranded break at MAT, the yeast mating type locus. To identify other proteins involved in this process, we examined whether extracts prepared from ho- mutants contain additional factors that bind near the recognition sequence for Ho. Using an electrophoretic mobility shift assay, we isolated a chromatographic fraction that contains an activity, named YZbp, which binds to two sequences flanking the recognition sequence at MATalpha and to one sequence overlapping it at MATa. MAT plasmids carrying mutations in the YZbp recognition sequence are cleaved by purified Ho at wild-type efficiencies in an in vitro assay. These same plasmids, however, are not cleaved by Ho inside cells, demonstrating that YZbp acts as a positive activator of in vivo cleavage. YZbp is present in all cell types, even those not undergoing mating type switching, suggesting that it has additional cellular functions. 相似文献
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