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31.
Mitochondrial gene order is not conserved in arthropods: prostriate and metastriate tick mitochondrial genomes 总被引:25,自引:15,他引:10
The entire mitochondrial genome was sequenced in a prostriate tick, Ixodes
hexagonus, and a metastriate tick, Rhipicephalus sanguineus. Both genomes
encode 22 tRNAs, 13 proteins, and two ribosomal RNAs. Prostriate ticks are
basal members of Ixodidae and have the same gene order as Limulus
polyphemus. In contrast, in R. sanguineus, a block of genes encoding NADH
dehydrogenase subunit 1 (ND1), tRNA(Leu)(UUR), tRNA(Leu)(CUN), 16S rDNA,
tRNA(Val), 12S rDNA, the control region, and the tRNA(Ile) and tRNA(Gln)
have translocated to a position between the tRNA(Glu) and tRNA(Phe) genes.
The tRNA(Cys) gene has translocated between the control region and the
tRNA(Met) gene, and the tRNA(Leu)(CUN) gene has translocated between the
tRNA(Ser)(UCN) gene and the control region. Furthermore, the control region
is duplicated, and both copies undergo concerted evolution. Primers that
flank these rearrangements confirm that this gene order is conserved in all
metastriate ticks examined. Correspondence analysis of amino acid and codon
use in the two ticks and in nine other arthropod mitochondrial genomes
indicate a strong bias in R. sanguineus towards amino acids encoded by
AT-rich codons.
相似文献
32.
Bradley RD; Adkins RM; Honeycutt RL; McDonald JH 《Molecular biology and evolution》1998,15(6):709-717
Using the strictly neutral model as a null hypothesis, we tested for
deviations from expected levels of nucleotide polymorphism at the alcohol
dehydrogenase locus (Adh-1) within and among four species of pocket gophers
(Geomys bursarius major, G. knoxjonesi, G. texensis llanensis, and G.
attwateri). The complete protein-encoding region was examined, and 10
unique alleles, representing both electromorphic and cryptic alleles, were
used to test hypotheses (e.g., the neutral model) concerning the
maintenance of genetic variation. Nineteen variable sites were identified
among the 10 alleles examined, including 9 segregating sites occurring in
synonymous positions and 10 that were nonsynonymous. Several statistical
methods, including those that test for within-species variation as well as
those that examine variation within and among species, failed to reject the
null hypothesis that variation (both within and between species of Geomys)
at the Adh locus is consistent with the neutral theory. However, there was
significant heterogeneity in the ratio of polymorphism to divergence across
the gene, with polymorphisms clustered in the first half of the coding
region and fixed differences clustered in the second half of the gene. Two
alternative hypotheses are discussed as possible explanations for this
heterogeneity: an old balanced polymorphism in the first half of the gene
or a recent selective sweep in the second half of the gene.
相似文献
33.
34.
Src homology 2 (SH2) domains mediate protein-protein interactions by recognizing phosphotyrosine (pY)-containing sequences of target proteins. In all of the SH2 domain-pY peptide interactions described to date, the SH2 domain binds to a single pY peptide. Here, determination of the cocrystal structure of the N-terminal SH2 domain of phosphatase SHP-2 bound to a class IV peptide (VIpYFVP) revealed a noncanonical 1:2 (protein-peptide) complex. The first peptide binds in a canonical manner with its pY side chain inserted in the usual binding pocket, while the second pairs up with the first to form two antiparallel β-strands that extend the central β-sheet of the SH2 domain. This unprecedented binding mode was confirmed in the solution phase by NMR experiments and shown to be adopted by pY peptides derived from cellular proteins. Site-directed mutagenesis and surface plasmon resonance studies revealed that the binding of the first peptide is pY-dependent, but phosphorylation is not required for the second peptide. Our findings suggest a potential new function for the SH2 domain as a molecular clamp to promote dimerization of signaling proteins. 相似文献
35.
36.
Klejbor I Myers JM Hausknecht K Corso TD Gambino AS Morys J Maher PA Hard R Richards J Stachowiak EK Stachowiak MK 《Journal of neurochemistry》2006,97(5):1243-1258
Developing and mature midbrain dopamine (DA) neurons express fibroblast growth factor (FGF) receptor-1 (FGFR1). To determine the role of FGFR1 signaling in the development of DA neurons, we generated transgenic mice expressing a dominant negative mutant [FGFR1(TK-)] from the catecholaminergic, neuron-specific tyrosine hydroxylase (TH) gene promoter. In homozygous th(tk-)/th(tk-) mice, significant reductions in the size of TH-immunoreactive neurons were found in the substantia nigra compacta (SNc) and the ventral tegmental area (VTA) at postnatal days 0 and 360. Newborn th(tk-)/th(tk-) mice had a reduced density of DA neurons in both SNc and VTA, and the changes in SNc were maintained into adulthood. The reduced density of DA transporter in the striatum further demonstrated an impaired development of the nigro-striatal DA system. Paradoxically, the th(tk-)/th(tk-) mice had increased levels of DA, homovanilic acid and 3-methoxytyramine in the striatum, indicative of excessive DA transmission. These structural and biochemical changes in DA neurons are similar to those reported in human patients with schizophrenia and, furthermore, these th(tk-)/th(tk-) mice displayed an impaired prepulse inhibition that was reversed by a DA receptor antagonist. Thus, this study establishes a new developmental model for a schizophrenia-like disorder in which the inhibition of FGF signaling leads to alterations in DA neurons and DA-mediated behavior. 相似文献
37.
38.
Jeffrey J. Hard William E. Bradshaw Christina M. Holzapfel 《Journal of evolutionary biology》1993,6(5):707-723
Demographic and phenological traits compose the basic elements of an insect's life-history strategy in a seasonal environment. An insect's long-term fitness depends on its ability to exploit favorable conditions, to avoid unfavorable conditions, and to convert from one life style to the other. For the pitcher-plant mosquito, Wyeomyia smithii, we show that genetic variation exists in both development time (a demographic trait) and critical photoperiod (a phenological trait) in six populations spanning much of the species' geographical range. During the northward range expansion of W. smithii in North America, these traits have evolved independently under strong directional and stabilizing selection. The correlated response in critical photoperiod to divergent selection on development time reveals significantly positive genetic correlations in five populations and a negative correlation in one population. The positive correlations form a genetically coordinated phenotype: faster developing individuals use a shorter photoperiodic switch point and are able to exploit the late favorable season; slower developing individuals use a longer photoperiodic switch point and are able to avoid extending development into the unfavorable season. This genetic coordination of demography and phenology has not, however, prevented their independent evolution. We propose that evolutionary flexibility in W. smithii may arise in part from the reorganization of their genetic architecture following repeated founder events during their northward invasion of North America. 相似文献
39.
Gordon C. Hard Carolyn Brown J. B. Wroblewski Robert L. Noble 《In vitro cellular & developmental biology. Plant》1982,18(10):872-883
Summary Two mixed cell lines designated REN-1 and REN-2 were established successfully in continuous in vitro culture from subcutaneously
propagated transplant tissue derived from a nephroblastoma which had occurred spontaneously in an Nb hooded rat. In monolayer
culture the lines consisted of clumps, islands, and cords of densely crowded, small basophilic cells of epithelioid character,
together with mesenchymelike cells occupying the intervening spaces. The proportion of epithelioid cells to mesenchyme could
be enhanced by high seeding densities and the intermittent application ofcishydroxyproline to the medium. A third cell form with the appearance of more mature epithelium was observed as a later development
in one of the monolayer cultures (REN-1). This larger epithelial cell and a homogeneous mesenchymal population were isolated
as cloned cell lines from REN-1 (REN-1-C/2 and REN-1-C/1, respectively), but attempts to clone the dominant basophilic epithelioid
cell were not successful. Light and electron microscopy indicated the small, basophilic epithelioid cells to be morphologically
consistent with the undifferentiated embryonal blast cells of the parent tumor. They were a distinctive population unlike
known malignant cell lines representative of chemically transformed rat kidney mesenchyme and epithelium. The mesenchymelike
cells present in the uncloned cell lines, and cloned in REN-1-C/1, were fibroblasts by ultrastructural criteria and therefore
distinct from the epithelioid moiety. Ultrastructurally the larger epithelium cloned in REN-1-C/2 displayed the features of
differentiated renal epithelium. Subcutaneous transplantation in syngeneic and allogeneic recipients showed the uncloned parent
cell lines containing the basophilic epithelioid population to be highly tumorigenic, producing rapidly growing tumors that
were unequivocal nephoblastomas. The mesenchymal clone, REN-1-C/1, was also tumorigenic but, consistent with its fibroblastic
nature, produced only fibrosarcomas on transplantation. The mature epithelial clone, REN-1-C/2, transplanted as an anaplastic
carcinoma with limited tubule formation. Because of their distinctive morphology and growth behavior, and their ability to
proliferate into nephroblastomas on transplantation, the dominant population of basophilic epithelioid cells in the parent
uncloned cell lines is considered to represent neoplastic kidney cells of undifferentiated embryonal type. The possible host
origin of the mesenchymal population from the supporting stroma of the original transplantation tumor is suggested in discussion.
This investigation was supported by research grants CA-24216 and CA-12227 awarded by the National Cancer Institute, Department
of Health and Human Services, and in part by the National Cancer Institute of Canada. 相似文献
40.
Epistasis and the Genetic Divergence of Photoperiodism between Populations of the Pitcher-Plant Mosquito, Wyeomyia Smithii 下载免费PDF全文
Parallel crosses between each of two southern (ancestral) and one northern (derived) population of the pitcher-plant mosquito, Wyeomyia smithii, were made to determine the genetic components of population divergence in critical photoperiod, a phenological trait that measures adaptation to seasonality along a climatic gradient. Joint scaling tests were used to analyze means and variances of first- and second-generation hybrids in order to determine whether nonadditive genetic variance, especially epistatic variance, contributed to divergence in critical photoperiod. In both crosses, digenic epistatic effects were highly significant, indicating that genetic divergence cannot have resulted solely from differences in additively acting loci. For one cross that could be tested directly for such effects, higher order epistasis and/or linkage did not contribute to the divergence of critical photoperiod between the constituent populations. 相似文献