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排序方式: 共有101条查询结果,搜索用时 31 毫秒
1.
Å. Franzén 《Zoomorphology》1984,104(3):140-146
Summary Differentiation of spermatids to mature spermatozoa in the bryozoan Tubulipora liliacea was studied by transmission electron microscopy. The spermatozoon of Tubulipora is of a filiform, modified type, and has evolved from the primitive type as an adaptation to a specialized biology of fertilization. The head of the spermatozoon consists of a small, conical acrosome capping an elongated, cylindrical, anteriorly tapering nucleus. A basal invagination in the nucleus contains the proximal portion of the axoneme and a dense attachment matrix. The flagellar axoneme has the typical 9+2 structure. Four elongated rodshaped mitochondria with typical cristae surround the axoneme in the cylindrical middle piece. Granular electron-dense material is accumulated in the form of four columns alternating with four long cylindrical mitochondria. The mitochondrial middle piece is separated externally from the tail region by an involution of the plasma membrane. The tail region contains a cytoplasmic sheath with accessory fibers surrounding the axoneme. Nine outer, coarse fibers extend posteriorly paralleling the nine doublets of the axoneme. The coarse fibers develop from electron-dense plate-like structures associated with the doublets of the axoneme. A characteristic feature in spermiogenesis is that spermatozoa develop in tetrads. There seem to be significant differences in spermatozoan ultrastructure between the three bryozoan classes Stenolaemata, Gymnolaemata, and Phylactolaemata. The differences indicate different lines of evolution of fertilization biology in these groups.Abbreviations used in the figures
a
acrosome
-
av
acrosomal vesicles
-
ax
axoneme
-
c
coarse fiber
-
d
electron dense rod
-
m
mitochondrion
-
mp
middle piece
- Scale
bars=0.5 m
-
mt
microtubule
-
n
nucleus
-
ne
nuclear envelope
-
p
nuclear protrusion
-
pm
plasma membrane
-
t
tail 相似文献
2.
Photo-CIDNP study of the interaction between the glucocorticoid receptor DNA-binding domain and glucocorticoid response elements 总被引:1,自引:0,他引:1
E. Kellenbach T. Härd R. Boelens K. Dahlman J. Carlstedt-Duke J. -Å. Gustafsson G. A. van der Marel J. H. van Boom B. Maler K. R. Yamamoto R. Kaptein 《Journal of biomolecular NMR》1991,1(1):105-110
Summary Photo-CIDNP studies were performed on two protein fragments that both contain the double zinc-finger DNA-binding domain of the glucocorticoid receptor. In the absence of DNA, Tyr452 and Tyr474 are polarised in both fragments while Tyr497 is not. Addition of a palindromic glucocorticoid response element (GRE) results in the suppression of Tyr474 polarization while the polarization of Tyr452 is unaffected. The same result is observed upon adding a half GRE to the protein fragment indicating that the suppression of Tyr474 polarization is not due to protein-protein contacts but to interaction with DNA. 相似文献
3.
Hedhammar M Rising A Grip S Martinez AS Nordling K Casals C Stark M Johansson J 《Biochemistry》2008,47(11):3407-3417
Spider dragline silk proteins, spidroins, have a tripartite composition; a nonrepetitive N-terminal domain, a central repetitive region built up from many iterated poly-Ala and Gly rich blocks, and a C-terminal nonrepetitive domain. It is generally believed that the repetitive region forms intermolecular contacts in the silk fibers, while precise functions of the terminal domains have not been established. Herein, thermal, pH, and salt effects on the structure and aggregation and/or polymerization of recombinant N- and C-terminal domains, a repetitive segment containing four poly-Ala and Gly rich coblocks, and combinations thereof were studied. The N- and C-terminal domains have mainly alpha-helical structure, and interestingly, both form homodimers. Dimerization of the end domains allows spidroin multimerization independent of the repetitive part. Reduction of an intersubunit disulfide in the C-terminal domain lowers the thermal stability but does not affect dimerization. The repetitive region shows helical secondary structure but appears to lack stable folded structure. A protein composed of this repetitive region linked to the C-terminal domain has a mainly alpha-helical folded structure but shows an abrupt transition to beta-sheet structures upon heating. At room temperature, this protein self-assembles into macroscopic fibers within minutes. The secondary structures of none of the domains are altered by pH or salt. However, high concentrations of phosphate affect the tertiary structure and accelerate the aggregation propensity of the repetitive region. Implications of these results for dragline spidroin behavior in solution and silk fiber formation are discussed. 相似文献
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7.
Matthew T. Webster Nona Kamgari Michele Perloski Marc P. Hoeppner Erik Axelsson ?ke Hedhammar Gerli Pielberg Kerstin Lindblad-Toh 《BMC genomics》2015,16(1)
Background
The domestic dog is a rich resource for mapping the genetic components of phenotypic variation due to its unique population history involving strong artificial selection. Genome-wide association studies have revealed a number of chromosomal regions where genetic variation associates with morphological characters that typify dog breeds. A region on chromosome 10 is among those with the highest levels of genetic differentiation between dog breeds and is associated with body mass and ear morphology, a common motif of animal domestication. We characterised variation in this region to uncover haplotype structure and identify candidate functional variants.Results
We first identified SNPs that strongly associate with body mass and ear type by comparing sequence variation in a 3 Mb region between 19 breeds with a variety of phenotypes. We next genotyped a subset of 123 candidate SNPs in 288 samples from 46 breeds to identify the variants most highly associated with phenotype and infer haplotype structure. A cluster of SNPs that associate strongly with the drop ear phenotype is located within a narrow interval downstream of the gene MSRB3, which is involved in human hearing. These SNPs are in strong genetic linkage with another set of variants that correlate with body mass within the gene HMGA2, which affects human height. In addition we find evidence that this region has been under selection during dog domestication, and identify a cluster of SNPs within MSRB3 that are highly differentiated between dogs and wolves.Conclusions
We characterise genetically linked variants that potentially influence ear type and body mass in dog breeds, both key traits that have been modified by selective breeding that may also be important for domestication. The finding that variants on long haplotypes have effects on more than one trait suggests that genetic linkage can be an important determinant of the phenotypic response to selection in domestic animals.Electronic supplementary material
The online version of this article (doi:10.1186/s12864-015-1702-2) contains supplementary material, which is available to authorized users. 相似文献8.
Boström M Markland K Sandén AM Hedhammar M Hober S Larsson G 《Applied microbiology and biotechnology》2005,68(1):82-90
The effect of changes in substrate feed rate during fedbatch cultivation was investigated with respect to soluble protein formation and transport of product to the periplasm in Escherichia coli. Production was transcribed from the PmalK promoter; and the cytoplasmic part of the production was compared with production from the PlacUV5 promoter. The fusion protein product, Zb-MalE, was at all times accumulated in the soluble protein fraction except during high-feed-rate production in the cytoplasm. This was due to a substantial degree of proteolysis in all production systems, as shown by the degradation pattern of the product. The product was also further subjected to inclusion body formation. Production in the periplasm resulted in accumulation of the full-length protein; and this production system led to a cellular physiology where the stringent response could be avoided. Furthermore, the secretion could be used to abort the diauxic growth phase resulting from use of the PmalK promoter. At high feed rate, the accumulation of acetic acid, due to overflow metabolism, could furthermore be completely avoided. 相似文献
9.
Landreh M Askarieh G Nordling K Hedhammar M Rising A Casals C Astorga-Wells J Alvelius G Knight SD Johansson J Jörnvall H Bergman T 《Journal of molecular biology》2010,404(2):328-336
Spider dragline silk, one of the strongest polymers in nature, is composed of proteins termed major ampullate spidroin (MaSp) 1 and MaSp2. The N-terminal (NT) domain of MaSp1 produced by the nursery web spider Euprosthenops australis acts as a pH-sensitive relay, mediating spidroin assembly at around pH 6.3. Using amide hydrogen/deuterium exchange combined with mass spectrometry (MS), we detected pH-dependent changes in deuterium incorporation into the core of the NT domain, indicating global structural stabilization at low pH. The stabilizing effects were diminished or abolished at high ionic strength, or when the surface-exposed residues Asp40 and Glu84 had been exchanged with the corresponding amides. Nondenaturing electrospray ionization MS revealed the presence of dimers in the gas phase at pH values below—but not above—6.4, indicating a tight electrostatic association that is dependent on Asp40 and Glu84 at low pH. Results from analytical ultracentrifugation support these findings. Together, the data suggest a mechanism whereby lowering the pH to < 6.4 results in structural changes and alteration of charge-mediated interactions between subunits, thereby locking the spidroin NT dimer into a tight entity important for aggregation and silk formation. 相似文献
10.
Sundqvist AK Björnerfeldt S Leonard JA Hailer F Hedhammar A Ellegren H Vilà C 《Genetics》2006,172(2):1121-1128
Dogs (Canis familiaris) were domesticated from the gray wolf (Canis lupus) at least 14,000 years ago, and there is evidence of dogs with phenotypes similar to those in modern breeds 4000 years ago. However, recent genetic analyses have suggested that modern dog breeds have a much more recent origin, probably <200 years ago. To study the origin of contemporaneous breeds we combined the analysis of paternally inherited Y chromosome markers with maternally inherited mitochondrial DNA and biparentally inherited autosomal microsatellite markers in both domestic dogs and their wild ancestor, the gray wolf. Our results show a sex bias in the origin of breeds, with fewer males than females contributing genetically, which clearly differs from the breeding patterns in wild gray wolf populations where both sexes have similar contributions. Furthermore, a comparison of mitochondrial DNA and Y chromosome diversity in dog groups recognized by the World Canine Organization, as well as in groups defined by the breeds' genetic composition, shows that paternal lineages are more differentiated among groups than maternal lineages. This demonstrates a lower exchange of males than of females between breeds belonging to different groups, which illustrates how breed founders may have been chosen. 相似文献