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Since there is no upper age limit for general organ donation, unlike heart valve donation, and since a quarter of all organ
donors are 65 years and older, we examined whether the heart valves from these donors are suitable as allografts. In the period
1999–2004 the aortic valve and pulmonary valve of 100 organ donors above 65 years of age were examined to establish whether
they would have been suitable as valve grafts. To compare the valve grafts above and below the age limit of 65 years, we used
data on the aortic and pulmonary valves of 380 organ donors below the age limit in the same time period. Examination of the
200 heart valves showed that – just like valves from donors below the age limit – 100 of them would have met the medical quality
standards for transplantation, which discriminate among optimal, suitable and unsuitable tissue morphology. The morphological
suitability of the aortic valves decreases rapidly during the 4th decade of life and near to the age limit only 6% of them
are accepted as grafts. The rate of potentially acceptable aortic valve grafts from organ donors aged over 65 years of 15%
is also small. By contrast, the pulmonary valves are not affected by age-related tissue changes that might reduce their transplantability.
The predominant majority (85%) of potential pulmonary valve grafts from organ donors over 65 years of age fulfilled the acceptance
criteria, half of them (48%) even showing good tissue quality. In light of these results the age limit was raised to 70 years
in 2005. 相似文献
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Localization of acetylcholine receptors and synaptic ultrastructure at nerve-muscle contacts in culture: dependence on nerve type 总被引:7,自引:6,他引:1 下载免费PDF全文
In cultures of xenopus myotomal muscle cells and spinal cord (SC) some of the nerve-muscle contacts exhibit a high density of acetylcholine receptors (AchRs [Anderson et al., 1977, J. Physiol. (Lond.). 268:731- 756,757-773]) and synaptic ultrastructure (Weldon and Cohen, 1979, J. Neurocytol. 8:239-259). We have examined whether similarly specialized contacts are established when the muscle cells are cultured with explants of xenopus dorsal root ganglia (DRG) or sympathetic ganglia (SG). The outgrowth from the ganglionic explants contained neuronal and non- neuronal cell processes. Although both types of processes approached within 100 A of muscle cells, synaptic ultrastructure was rarely observed at these contacts. Because patches of postsynaptic ultrastructure also develop on noncontacted muscle cells, the very few examples of contacts with such specializations probably occurred by chance. AChRs were stained with fluroscent α-bungarotoxin. More than 70 percent of the SC-contacted muscle cells exhibited a high receptor density along the path of contact. The corresponding values for DRG- and SG- contacted muscle cells were 10 and 6 percent. Similar values were obtained when the ganlionic and SC explants were cultured together in the same chamber. The few examples of high receptor density at ganglionic-muscle contacts resembled the characteristic receptor patches of noncontacted muscle cells rather than the narrow bands of high receptor density seen at SC-muscle contacts. In addition, more than 90 percent of these ganglionic- contacted muscle cells had receptor patches elsewhere, compared to less than 40 percent for the SC-contacted muscle cells. These findings indicate that the SC neurites possess a specific property which is important for the establishment of synaptically specialized contacts with muscle and that this property is lacking in the DRG and SG neurites. 相似文献
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Polymorphism and divergence at the 5' flanking region of the sex- determining locus, Sry, in mice 总被引:3,自引:0,他引:3
We have investigated patterns of evolution in the nonrecombining portion of
the Y chromosome in mice by comparing levels of polymorphism within Mus
domesticus with levels of divergence between M. domesticus and M. spretus.
A 1,277-bp fragment of noncoding sequence flanking the sex determining
locus (Sry) was PCR amplified, and 1,063 bases were sequenced and compared
among 20 M. domesticus and 1 M. spretus. Two polymorphic base substitutions
and two polymorphic insertion/deletion sites were identified within M.
domesticus; nucleotide diversity was estimated to be 0.1%. Divergence
between M. domesticus and M. spretus for this region (1.9%) was slightly
lower than the average divergence of single-copy nuclear DNA for these
species. Comparison of levels of polymorphism and divergence at Sry with
levels of polymorphism and divergence in the mitochondrial DNA control
region provided no evidence of a departure from the expectations of neutral
molecular evolution. These findings are consistent with the presumed lack
of function for much of the Y chromosome.
相似文献
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Nuclear pore complexes (NPCs) serve as transport channels across the nuclear membrane, a double lipid bilayer that physically
separates the nucleoplasm and cytoplasm of eukaryotic cells. New evidence suggests that the multiprotein nuclear pores also
play a role in chromatin organization and gene expression. Given the importance of NPC function, it is not surprising that
a growing list of human diseases and developmental defects have been linked to its malfunction. In order to fully understand
the functional repertoire of NPCs and their essential role for nuclear organization, it is critical to determine the sequence
of events that lead to the formation of nuclear pores. This is particularly relevant since NPC number, and possibly composition,
are tightly linked to metabolic activity. Most of our knowledge is derived from NPC formation that occurs in dividing cells
at the end of mitosis when the nuclear envelope (NE) and NPCs reform from disassembled precursors. However, NPC assembly also
takes place during interphase into an intact NE. Importantly, this process is not restricted to dividing cells but also occurs
during cell differentiation. Here, we will review aspects unique to this process, namely the regulation of nuclear expansion
and the mechanisms of fusion between the outer and inner nuclear membranes. We will then discuss conserved and diverging mechanisms
between post-mitotic and interphase assembly of the proteinaceous structure in light of recently published data. 相似文献
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Goldstein DB; Zhivotovsky LA; Nayar K; Linares AR; Cavalli-Sforza LL; Feldman MW 《Molecular biology and evolution》1996,13(9):1213-1218
It has recently been suggested that observed levels of variation at
microsatellite loci can be used to infer patterns of selection in genomes
and to assess demographic history. In order to evaluate the feasibility of
these suggestions it is necessary to know something about how levels of
variation at microsatellite loci are expected to fluctuate due simply to
stochasticity in the processes of mutation and inheritance (genetic
sampling). Here we use recently derived properties of the stepwise mutation
model to place confidence intervals around the variance in repeat score
that is expected at mutation-drift equilibrium and outline a statistical
test for whether an observed value differs significantly from expectation.
We also develop confidence intervals for the time course of the buildup of
variation following a complete elimination of variation, such as might be
caused by a selective sweep or an extreme population bottleneck. We apply
these methods to the variation observed at human Y-specific
microsatellites. Although a number of authors have suggested the
possibility of a very recent sweep, our analyses suggest that a sweep or
extreme bottleneck is unlikely to have occurred anytime during the last
approximately 74,000 years. To generate this result we use a recently
estimated mutation rate for microsatellite loci of 5.6 x 10(-4) along with
the variation observed at autosomal microsatellite loci to estimate the
human effective population size. This estimate is 18,000, implying an
effective number of 4,500 Y chromosomes. One important general conclusion
to emerge from this study is that in order to reject mutation-drift
equilibrium at a set of linked microsatellite loci it is necessary to have
an unreasonably large number of loci unless the observed variance is far
below that expected at mutation-drift equilibrium.
相似文献
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Timo Hetzer Achim Bräuning Hanns-Hubert Leuschner 《Trees - Structure and Function》2014,28(5):1279-1288