共查询到20条相似文献,搜索用时 0 毫秒
1.
Eleutherodactylus coqui develops directly from a large 3.5-mm egg to a froglet, without an intervening tadpole stage. We have examined the development
of the body wall, a structure whose behavior has been altered in this derived development. In an event that is unusual for
amphibian embryos, the yolk mass is secondarily surrounded by the body wall, which originates near the embryo’s trunk. The
epidermis of the body wall is marked by melanophores, and the rectus abdominis, which will form the ventral musculature, is
near its leading edge. As the body wall expands, the epidermis, melanophores, and rectus abdominis all move from the dorsal
side to close over the yolk at the ventral midline. The original ectoderm over the yolk undergoes apoptosis, as it is replaced
by body wall epidermis. Intact muscles are not required for ventral closure of the body wall, despite their normal presence
near the advancing edge. Comparative examination of embryos of Xenopus laevis and Rana pipiens suggests that ventral closure does not occur in species with tadpoles. The expansion of dorsal tissues over the yolk, as
illustrated by E. coqui, may have been important in the origin of amniote embryos.
Received: 23 April 1998 / Accepted: 28 June 1998 相似文献
2.
We tested the effects of noggin RNA from Xenopus laevis on axis induction in embryos of a direct developing frog, Eleutherodactylus coqui. We microinjected noggin RNA into one blastomere of 4-cell embryos at the site close to the animal pole, and found that overexpression
of noggin RNA is not only sufficient to induce additional axes but also induces heads with eyes. We also injected noggin RNA
into 8-cell or 16-cell embryos in various sites, including the marginal zone, above the marginal zone, and the vegetal pole,
and found the formation of a complete secondary axis in all three types of injection. These effects of X. laevis noggin RNA on the E. coqui embryo are remarkably different from those found in the X. laevis embryo itself. It has been shown previously that overexpression of noggin RNA on the ventral side of the normal X. laevis embryo induces only a partial axis, with no head structures. We show here that the failure of noggin induction of a complete
axis when overexpressed on the ventral side of the X. laevis embryos is not due to an insufficient amount of RNA injected. Also, the failure is unlikely due to inhibition from the primary
axis since noggin RNA can induce duplicated head structures on opposite sides of UV-irradiated X. laevis embryos. There appear to be fundamental differences in the responses of E. coqui and X. laevis embryos to exogenous noggin RNA. We propose that these differences stem from an alteration in cytoplasmic arrangements that
occurred during evolution of this large egg.
Received: 26 July 1999 / Accepted: 1 September 1999 相似文献
3.
Peronella japonica, a sand dollar, forms an abbreviated pluteus larva and metamorphoses within 3 days without feeding. In the present study,
the cleavage pattern of Peronella embryos was found to be quite irregular in the vegetal blastomeres at the fourth cleavage. Less than half of the embryos examined
formed four typical micromeres. The majority formed zero, one, two or three typical micromeres of regular size, and the blastomere(s)
remaining in the vegetal-most region was atypical in size and/or its direction of division. Most embryos were able to form
pluteus larvae and a considerable proportion of these metamorphosed into juvenile sea urchins, regardless of whether or not
they had formed four typical micromeres of regular size, although embryos which formed no typical micromeres developed into
pluteus larvae less frequently. The micromere progeny in Peronella embryos form skeletogenic mesenchyme cells. The average numbers of skeletogenic mesenchyme cells in the three sand dollar
species, Clypeaster japonicus, Astriclypeus manni and P. japonica were 62, 122 and 219, respectively. In these species, the skeletogenic mesenchyme cell-specific glycoprotein (msp130) was
first detected immediately after ingression of the primary mesenchyme cells, spicules appeared at the early gastrula stage
and triradiate spicules were found in late gastrulae. Appearance of these characteristics was markedly accelerated in the
embryos of A. manni and P. japonica in comparison with those of C. japonicus. Each step in the formation of larval spicules was equally accelerated in A. manni and P. japonica, although the appearance of the adult skeleton was further accelerated in P. japonica in comparison with A. manni, possibly because of omission of the four- to eight-armed pluteus stages.
Received: 1 September 1995 / Accepted in revised form: 21 May 1995 相似文献
4.
5.
Arthropods are the most diverse and speciose group of organisms on earth. A key feature in their successful radiation is
the ease with which various appendages become readily adapted to new functions in novel environments. Arthropod limbs differ
radically in form and function, from unbranched walking legs to multibranched swimming paddles. To uncover the developmental
and genetic mechanisms underlying this diversification in form, we ask whether a three-signal model of limb growth based on
Drosophila experiments is used in the development of arthropod limbs with variant shape. We cloned a Wnt-1 ortholog (Tlwnt-1) from Triops longicaudatus, a basal crustacean with a multibranched limb. We examined the mRNA in situ hybridization pattern during larval development
to determine whether changes in wg expression are correlated with innovation in limb form. During larval growth and segmentation Tlwnt-1 is expressed in a segmentally reiterated pattern in the trunk. Unexpectedly, this pattern is restricted to the ventral portion
of the epidermis. During early limb formation the single continuous stripe of Tlwnt-1 expression in each segment becomes ventrolaterally restricted into a series of shorter stripes. Some but not all of these
shorter stripes correspond to what becomes the ventral side of a developing limb branch. We conclude that the Drosophila model of limb development cannot explain all types of arthropod proximodistal outgrowths, and that the multibranched limb
of Triops develops from an early reorganization of the ventral body wall. In Triops, Tlwnt-1 plays a semiconservative role similar to that played by Drosophila wingless in segmentation and limb formation, and morphological innovation in limb form arises in part through an early modulation
in the expression of the Tlwnt-1 gene.
Received: 22 September 1998 / Accepted: 12 January 1999 相似文献
6.
J. E. Flanigan M. Guppy 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):135-145
In aestivation the metabolic rate of the Australian desert frog Neobatrachus kunapalari was 50–67% lower than in the non-aestivating state. The rate of O2 consumption of isolated muscle, skin and brain was measured in both metabolic states. The average rate of O2 consumption of muscle was 30% lower and brain 50% lower in aestivating frogs, while the rate of O2 consumption of skin was the same. The reduction in muscle could account for a large proportion of whole animal metabolic
depression. To look for evidence of a reduction in energy demand in the tissues we measured the ouabain-sensitive fraction
of tissue rate of O2 consumption, which is considered to be the proportion of metabolism used for transmembrane Na+/K+ pumping. Ouabain inhibited the in vitro rate of O2 consumption of skin by a average of 20% and of brain by an average of 30%. However, in muscle, ouabain stimulated in vitro
O2 consumption. Despite the 50% reduction in the in vitro rate of O2 consumption of brain during aestivation, neither the ouabain-sensitive nor ouabain-insensitive fractions were found be statistically
different, possibly because of the large individual variation in the degree of ouabain inhibition. A reduction in the level
of ion pumping during aestivation was therefore not demonstrated in any tissue. Measurement of the level of the enzyme Na+K+-ATPase in skeletal muscle, ventricle, kidney and brain showed that there was no change in the amount of this enzyme in the
aestivating frogs. Measurement of the levels of adenylates in muscle and liver showed that the adenylate energy charge was
maintained in aestivation, but that there was a reduction in ATP in liver and a reduction in the level of total adenylates
in both tissues, which could be an adaptation of the tissues to a lower energy turnover.
Accepted: 22 July 1996 相似文献
7.
Flow cytometric analysis of the chromosomes and stability of a wheat cell-culture line 总被引:3,自引:0,他引:3
T. Schwarzacher M. L. Wang A. R. Leitch G. Moore J. S. Heslop-Harrison N. Miller 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):91-97
A rapidly growing, long-term suspension culture derived from Triticum aestivum L. (wheat) was synchronized using hydroxyurea and colchicine, and a chromosome suspension with chromosomes was made. After staining with the DNA-specific fluorochromes Hoechst 33258 and Chromomycin univariate and bivariate flow-cytometry histograms showed 15 clearly resolved peaks corresponding to individual chromosome
types or groups of chromosomes with similar DNA contents. The flow karyotype was closely similar to a histogram of DNA content
measurements of Feulgen-stained chromosomes made by microdensitometry. We were able to show the stability of the flow karyotype
of the cell line over a year, while a parallel subculture had a slightly different, stable, karyotype following different
growth conditions. The data indicate that flow cytometric analysis of plant karyotypes enables accurate, statistically precise
chromosome classification and karyotyping of cereals. There was little overlap between individual flow-histogram peaks, so
the method is useful for flow sorting and the construction of chromosome specific-recombinant DNA libraries. Using bivariate
analysis, the AT:GC ratio of all the chromosomes was remarkably similar, in striking contrast to mammalian flow karyotypes.
We speculate about a fundamental difference in organization and homogenization of DNA sequences between chromosomes within
mammalian and plant genomes.
Received: 24 April 1996 / Accepted: 24 May 1996 相似文献
8.
Gliadin polymorphism in wild and cultivated einkorn wheats 总被引:4,自引:0,他引:4
M. Ciaffi L. Dominici D. Lafiandra 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):68-74
To study the relationships between different species of the Einkorn group, 408 accessions of Triticum monococcum, T. boeoticum, T. boeoticum ssp. thauodar and T. urartu were analyzed electrophoretically for their protein composition at the Gli-1 and Gli-2 loci. In all the species the range of allelic variation at the loci examined is remarkable. The gliadin patterns of T. monococcum and T. boeoticum were very similar to one another but differed substantially from those of T. urartu. Several accessions of T. boeoticum and T. monococcum were shown to share the same alleles at the Gli-1 and Gli-2 loci, confirming the recent nomenclature that considers these wheats as different subspecies of the same species, T. monococcum. The gliadin composition of T. urartu resembled that of the A genome of polyploid wheats more than did T. boeoticum or T. monococcum, supporting the hypothesis that T. urartu, rather than T. boeoticum, is the donor of the A genome in cultivated wheats. Because of their high degree of polymorphism the gliadin markers may
help in selecting breeding parents from diploid wheat germ plasm collections and can be used both to search for valuable genes
linked to the gliadin-coding loci and to monitor the transfer of alien genes into cultivated polyploid wheats.
Received: 8 July 1996 / Accepted: 12 July 1996 相似文献
9.
Polymorphism, distribution, and segregation of AFLP markers in a doubled haploid rice population 总被引:18,自引:0,他引:18
M. Maheswaran P. K. Subudhi S. Nandi J. C. Xu A. Parco D. C. Yang N. Huang 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):39-45
We exploited the newly developed amplified fragment length polymorphism (AFLP) technique to study the polymorphism, distribution
and inheritance of AFLP markers with a doubled haploid rice population derived from ‘IR64’/‘Azucena’. Using only 20 pairs
of primer combinations, we detected 945 AFLP bands of which 208 were polymorphic. All 208 AFLP markers were mapped and distributed
over all 12 chromosomes. When these were compared with RFLP markers already mapped in the population, we found the AFLP markers
to be highly polymorphic in rice and to follow Mendelian segregation. As linkage map of rice can be generated rapidly with
AFLP markers they will be very useful for marker-assisted backcrossing.
Received: 11 April 1996 / Accepted: 14 June 1996 相似文献
10.
MAP kinase signaling during pollen development 总被引:1,自引:0,他引:1
E. Heberle-Bors Viktor Voronin Alisher Touraev Pilar Sanchez Testillano Maria Carmen Risueño Cathal Wilson 《Sexual plant reproduction》2001,14(1-2):15-19
The stereotypical events of pollen grain maturation and its coordinated development with other flower tissues requires the
interplay of different signalling pathways in order to ensure efficient fertilisation and, eventually, seed set. In recent
years evidence has accumulated that members of the mitogen-activated protein kinase (MAP kinase) family are expressed in pollen
and may function as regulators of both pollen development and germination. In this review we describe what is known about
MAP kinases in pollen and discuss their possible function(s) in pollen biology.
Received: 14 December 2000 / Accepted: 6 June 2001 相似文献
11.
Mauro Vallarino Maura Mathieu Claudia Pinelli R. K. Rastogi 《Cell and tissue research》1998,293(1):47-55
Immunocytochemical distribution of the atrial natriuretic factor (ANF) has been studied in the brain and pituitary of the
anuran Rana esculenta during development and in juvenile animals. Using human ANF and rat α-ANF antisera, immunoreactive cell bodies and nerve
fibers were revealed in stage II–III tadpoles and in successive larval stages. Soon after hatching, stages II–III, the ANF-like-immunoreactive
elements were confined to the preoptic area-median eminence complex. During successive stages of development, new groups of
ANF-immunoreactive cell bodies appeared. In larval stage VI, immunoreactive perikarya were found in the rostral part of the
anteroventral area of the thalamus and numerous ANF-like-immunoreactive cells appeared in the pars distalis of the pituitary.
In larval stages XIV and XVIII, the distribution of ANF immunoreactivity was virtually similar. The ANF-immunoreactive cells
in the preoptic nucleus and in the pituitary pars distalis were comparatively more abundant than in stage VI. During the metamorphic
climax (stages XXI–XXII), a new group of ANF-immunoreactive cell bodies appeared in the rostral part of the ventrolateral
area of the thalamus. During this stage, ANF-immunoreactive fiber projections were found in the pars intermedia for the first
time. However, the pars distalis cells were very weakly immunofluorescent. The pattern of ANF immunoreactivity in the brain
of juvenile animals was very similar to that described for stages XXI and XXII, whereas the pars distalis cells showed no
immunoreactivity. It is conceivable that, early during development, ANF-related peptides may be involved in the regulation
of pituitary secretion by means of autocrine mechanisms or may act as a classic pituitary hormone.
Received: 28 July 1997 / Accepted: 8 December 1997 相似文献
12.
Highly polymorphic microsatellites of rice consist of AT repeats, and a classification of closely related cultivars with these microsatellite loci 总被引:20,自引:3,他引:20
H. Akagi Y. Yokozeki A. Inagaki T. Fujimura 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):61-67
Microsatellites consisting of AT repeats are highly polymorphic in rice genomes and can be used to distinguish between even
closely related japonica cultivars in Japan. Polymorphisms of 20 microsatellite loci were determined using 59 japonica cultivars,
including both domestic and modern Japanese cultivars. Although the polymorphisms of these 20 microsatellite loci indicated
that the Japanese cultivars were genetically quite similar, microsatellites consisting of AT repeats showed high gene diversity
even among such closely related cultivars. Combinations of these hypervariable microsatellites can be employed to classify
individual cultivars, since the microsatellites were stable within each cultivar. An identification system based on these
highly polymorphic microsatellites could be used to maintain the purity of rice seeds by eliminating contamination. A parentage
diagnosis using 17 polymorphic microsatellite loci clearly demonstrated that plants which carried desired chromosome regions
had been selected in breeding programs. Thus, these hypervariable microsatellites consisting of AT repeats should promote
the selection of plants which carry desired chromosomes from genetically similar parents. Backcrossing could also help to
eliminate unnecessary chromosome regions with microsatellite polymorphisms at an early stage in breeding programs.
Received: 8 July 1996 / Accepted: 12 July 1996 相似文献
13.
F. A. Davidson B. D. Sleeman A. D. M. Rayner J. W. Crawford K. Ritz 《Journal of mathematical biology》1997,35(5):589-608
Under a variety of conditions, the hyphal density within the expanding outer edge of growing fungal mycelia can be spatially
heterogeneous or nearly uniform. We conduct an analysis of a system of reaction-diffusion equations used to model the growth
of fungal mycelia and the subsequent development of macroscopic patterns produced by differing hyphal and hence biomass densities.
Both local and global results are obtained using analytical and numerical techniques. The emphasis is on qualitative results,
including the effects of changes in parameter values on the structure of the solution set.
Received 22 November 1995; received in revised form 17 May 1996 相似文献
14.
Makoto Mizuno Takashi Takabatake Tadashi C. Takahashi K. Takeshima 《Development genes and evolution》1997,207(3):167-176
pax-6 is thought to be a master control gene of eye development in species ranging from insects to mammals. We have isolated a pax-6 cDNA homolog of the newt, Cynops pyrrhogaster. RT-PCR and sequence analyses predicted four alternatively spliced forms derived from inclusion or exclusion of the region
corresponding to exons 5a and 12 in the human pax-6 ortholog. This gene shared extensive sequence identitiy and similar expression patterns with those of mouse and zebrafish.
pax-6 signal was first detected at the anterior ridge of the neural plate, and later at the eye and nasal primordium and in the
central nervous system – except for the midbrain. The injection of sonic hedgehog (shh) RNA inhibited the expression of pax-6 within the optic vesicle and disturbed eye cup formation. A similar suppressive effect of shh was also observed in the conjugation of the animal caps preloaded with exogenous shh and noggin mRNA, which was used as an inducer of pax-6. In contrast, shh injection had no effect on the expression of pax-6 in the surface ectoderm overlying the optic cup, suggesting that the expression of pax-6 in the surface ectoderm is not regulated by shh in vivo. Moreover, we found transient activation of pax-6 in animal cap explants at the sibling stage of mid-late gastrula. This observation raises the possibility that the ectoderm
is competent to the lens-inducing signal at a stage as early as mid gastrula.
Received: 5 February 1997 / Accepted: 30 April 1997 相似文献
15.
The ratio of loculus volume to the volume of the entire anther began to increase from the microspore mother cell stage and
reached 32.3% at anthesis. The content of the loculus was examined in Lilium during pollen development and two waves could be distinguished. From the premeiotic stage until the vacuolated microspore
stage, the loculus consisted of neutral polysaccharides, pectins and proteins. These substances originated from tapetal activity
from the premeiotic stage until the young microspore stage. Dictyosomes and rough endoplasmic reticulum seemed to be involved
in tapetal secretion, although, in some mitochondria, vesicles progressively developed as early as premeiosis and increased
until the young microspore stage, which could reveal their involvement in the secretion process. At this stage, numerous cytoplasmic
vesticles containing material similar to the locular material fused with the plasma membrane of the tapetum so that vesicle
content was in contact with the loculus. It seems that tapetal and callose wall degradation at the late tetrad stage may also
have contributed to the production of material in the loculus. From pollen mitosis to anthesis, the anther loculus contained
mainly the pollenkitt which was synthesized in the tapetum between the young microspore stage and the vacuolated microspore
stage. At the young microspore stage, proplastids divided and developed into elaioplasts and smooth endoplasmic reticulum
(SER) increased dramatically. Pollenkitt had a double origin: some droplets were extruded directly from the plastid stroma
through the plastid envelopes; the others were unsaturated lipid globules, which presumably derived from the interaction between
SER saccules and plastids.
Received: 2 September 1997 / Revision accepted: 12 March 1998 相似文献
16.
17.
We have studied the role of the wingless gene in embryonic brain development of Drosophila. wingless is expressed in a large domain in the anlage of the protocerebrum and also transiently in smaller domains in the anlagen
of the deutocerebrum and tritocerebrum. Elimination of the wingless gene in null mutants has dramatic effects on the developing protocerebrum; although initially generated, approximately one
half of the protocerebrum is deleted in wingless null mutants by apoptotic cell death at late embryonic stages. Using temperature sensitive mutants, a rescue of the mutant
phenotype can be achieved by stage-specific expression of functional wingless protein during embryonic stages 9–10. This time
period correlates with that of neuroblast specification but preceeds the generation and subsequent loss of protocerebral neurons.
Ectopic wingless over-expression in gain-of-function mutants results in dramatically oversized CNS. We conclude that wingless is required for the development of the anterior protocerebral brain region in Drosophila. We propose that an important role of wingless in this part of the developing brain is the determination of neural cell fate.
Received: 7 October 1997 / Accepted: 30 December 1997 相似文献
18.
A simple and reproducible in vitro system is described for the synthesis of Pisolithus-Eucalyptus grandis ectomycorrhizae. Hyphal discs from actively growing colonies were placed in large petri dishes containing minimum nutrient
agar overlaid with cellophane and allowed to grow for 7 days. Seeds were then surface sterilized and placed above the expanding
fungal colonies and the plates slanted. Seedlings that germinated and grew in the presence of fungal hyphae had twice as many
lateral root tips as seedlings that germinated before they were transferred onto hyphal mats. In addition, the lateral root
tips of inoculated seedlings had a faster maturation rate and emerged closer to the primary root apex than non-inoculated
seedlings. All lateral tips emerged in contact with fungal hyphae and the differentiation of ectomycorrhizae was followed
by examining lateral tips basipetally along a single primary root. Typical ectomycorrhizae had formed on 4-day-old lateral
tips, i.e. a mantle, radially elongated epidermal cells and a Hartig net commencing about 0.3 mm behind the lateral root apex.
Thereafter, the mantle continued to thicken and the apical meristem diminished. The Hartig net often surrounded the apex of
11- to 12-day-old lateral root tips. This model system will facilitate detailed studies on synchronized ectomycorrhizal development
and associated molecular and biochemical changes.
Accepted: 12 January 1996 相似文献
19.
J. Yamaguchi S. Itoh T. Saitoh A. Ikeda T. Tashiro Y. Nagato 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,98(1):32-38
β-Amylase deficiency in various cultivars of rice was examined at the molecular level. Using an antibody against β-amylase
purified from germinating seeds of rice, we were able to demonstrate the expression and organization of the β-amylase gene
in normal and deficient cultivars. Although β-amylase is a starch-hydrolyzing enzyme, as is α-amylase, the β-amylase protein/gene
is expressed differently from the α-amylase protein/gene; i.e. (1) β-amylase is synthesized only in aleurone cells, (2) the
enzyme production in the embryo-less half-seeds is not under hormonal control. We identified some cultivars of rice that are
deficient for β-amylase activity. We present new evidence that synthesis is blocked at the level of mRNA synthesis in the
deficient cultivars. The usefulness of β-amylase as a crop trait is also discussed.
Received: 8 May 1998 / Accepted: 5 June 1998 相似文献
20.
T. Krugman A. Korol E. Nevo J. W. Snape O. Levy B. Rubin 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):46-51
Chlorotoluron is a selective phenylurea herbicide widely used for broad-leaved and annual grass weed control in cereals. Variation in the response to chlorotoluron (CT) was found in both hexaploid bread wheat (Triticum aestivum L.) and wild tetraploid wheat (Triticum dicoccoides KöRN.). Here, we describe the comparative mapping of the CT resistance gene (Su1) on chromosome 6B in bread and wild wheat using RFLP markers. In bread wheat, mapping was based on 58 F4 single-seed descent (SSD) plants of the cross between a genotype sensitive to chlorotoluron, ‘Chinese Spring’ (CS), and a resistant derivative, the single chromosome substitution line, CS (‘Cappele-Desprez’ 6B) [CS (CAP6B). In T dicoccoides, mapping was based on 37 F2 plants obtained from the cross between the CT-susceptible accession B-7 and the resistant accession B-35. Nine RFLP probes spanning the centromere were chosen for mapping. In bread wheat Su1 was found to be linked to α-Amy-1 (9.84 cM) and Xpsr371 (5.2 cM), both on the long arm of 6B, and Nor2 (2.74 cM) on the short arm. In wild wheat the most probable linkage map was Nor2-Xpsr312-Su1-Pgk2, and the genetic distances between the genes were 24.8cM, 5.3cM, and 6.8cM, respectively. These results along with other published map data indicate that the linear order of the genes is similar to that found in T. aestivum. The results of this study also show that the Su1 gene for differential response to chlorotoluron has evolved prior to the domestication of cultivated wheat and not in response to the development and use of chemicals. 相似文献