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排序方式: 共有232条查询结果,搜索用时 15 毫秒
1.
Dr. Hansjörg Wunderer Serge Picaud Nicolas Franceschini 《Cell and tissue research》1989,257(3):565-576
Summary Single photoreceptor cells in the compound eye of the housefly Musca domestica were selectively illuminated and subsequently compared electron-microscopically with the unilluminated photoreceptors in the immediate surroundings. The rhabdomeres of the illuminated cells remain largely unaffected, but the cells show an increase in the number of coated pits, various types of vesicles, and degradative organelles; some of the latter organelles are described for the first time in fly photoreceptors. Coated pits are found not only at the bases of the microvilli, but also in other parts of the plasma membrane. Degradative organelles, endoplasmic reticulum (ER) and mitochondria aggregate in the perinuclear region. The rough ER and smooth ER are more elaborate, the number of Golgi stacks, free ribosomes and polysomes is increased, and the shape and distribution of heterochromatin within the nuclei are altered. Illuminated photoreceptors also interdigitate extensively with their neighbouring secondary pigment cells. These structural changes in illuminated fly photoreceptor cells indicate an increase in membrane turnover and cellular metabolism. When applied to the eye, Lucifer Yellow spreads into the extracellular space and is taken up only by the illuminated photoreceptor cells. These cells show the same structural modifications as above. Horseradish peroxidase applied in the same way is observed in pinocytotic vesicles and degradative organelles of the illuminated cells. Hence, the light-induced uptake of extracellular compounds takes place in vivo at least partially as a result of an increase in pinocytosis. 相似文献
2.
3.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
4.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
5.
A chlorophyll b-less mutant of Chlamydomonas reinhardtii (Pg
27) was isolated after UV irradiation of the wild type cells. This photosynthetically competent mutant totally lacks chlorophyll b and the CP2 chlorophyll-protein complex. However, SDS-PAGE, proteolytic digestions and immunodetections demonstrated that the 24–25 Kd apoproteins of the lacking CP2 complex are still present in thylakoids of the Pg27 mutant. It is concluded that this CP2-less mutant is affected in the biosynthesis pathway of chlorophyll b.This CP2-less mutant was crossed with a CP1-less mutant (Fl5) Fluorescence emission spectra and fluorescence inductions in the presence of DCMU were analysed in the resulting (cp
2
–
, cp
1
+
), (cp
2
+
, cp
1
–
), (cp
2
+
, cp
1
+
), cp
2
–
, cp
1
–
)tetratype. Differences in PS 2 optical cross section and in the relative amplitude or localisation of fluorescence emission peaks fit well with a quadripartite model where PS1 and PS2 would each correspond to a reaction centre core complex (CP1 and CP2 respectively) associated to a light harvesting antenna (LHC1 and LHC2 respectively). The occurrence of energy transfers from PS1 peripheral antenna to PS2 in the Fl
5 mutant shows that, in absence of CP1, at least a part of its associated PS1 light harvesting antenna migrates in the PS2 containing appressed thylakoids.Abbreviations Chl
Chlorophyll
- LHC
Light harvesting chl a/b complex
- CP2
Predominant form of LHC or SDS polyacrylamide gels
- WT
Wild type
- DM
Double mutant (cp
1
–
, cp
2
–
)
- SDS-PAGE
sodium dodecyl sulfate polyacrylamide gel electrophoresis
- DOC-PAGE
Deoxycholate polyacrylamide gel electrophoresis 相似文献
6.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
7.
8.
9.
A highly conserved nuclear gene for low-level phylogenetics: elongation factor-1 alpha recovers morphology-based tree for heliothine moths 总被引:8,自引:2,他引:6
Cho S; Mitchell A; Regier JC; Mitter C; Poole RW; Friedlander TP; Zhao S 《Molecular biology and evolution》1995,12(4):650-656
Molecular systematists need increased access to nuclear genes. Highly
conserved, low copy number protein-encoding nuclear genes have attractive
features for phylogenetic inference but have heretofore been applied mostly
to very ancient divergences. By virtue of their synonymous substitutions,
such genes should contain a wealth of information about lower-level
taxonomic relationships as well, with the advantage that amino acid
conservatism makes both alignment and primer definition straightforward. We
tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene
in the noctuid moth subfamily Heliothinae, which has probably diversified
since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing
heliothine groupings strongly supported by previous morphological and
allozyme studies. The single most parsimonious gene tree and the
neighbor-joining tree for all nucleotides show almost complete concordance
with the morphological tree. Homoplasy and pairwise divergence levels are
low, transition/transversion ratios are high, and phylogenetic information
is spread evenly across gene regions. The EF-1 alpha gene and presumably
other highly conserved genes hold much promise for phylogenetics of
Tertiary age eukaryote groups.
相似文献
10.
Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation. 相似文献