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951.
肿瘤干细胞及其耐药机制 总被引:3,自引:0,他引:3
肿瘤干细胞是存在于造血系统肿瘤和一些实体瘤中具有干细胞特性的细胞。肿瘤干细胞假说认为,经药物治疗后肿瘤复发和转移与肿瘤干细胞残存有密切关系。其原因可能是肿瘤干细胞高表达ABC转运蛋白和Bcl-2抗凋亡蛋白,同时其本身又具有一些干细胞特性。对肿瘤干细胞耐药机制的研究,将有助于发现新的肿瘤治疗靶点和更好的抗癌策略。 相似文献
952.
Epigenetic modifiers promote efficient generation of neural-like cells from bone marrow-derived mesenchymal cells grown in neural environment 总被引:2,自引:0,他引:2
Alexanian AR 《Journal of cellular biochemistry》2007,100(2):362-371
Understanding mechanisms that govern cell fate decisions will lead to developing techniques for induction of adult stem cell differentiation to desired cell outcomes and, thus, production of an autologos source of cells for regenerative medicine. Recently, we demonstrated that stem cells derived from adult central nervous system or bone marrow grown with other cell lineages or with more undifferentiated cells sometimes take on those characteristics. This indicates that manipulating extracellular factors may be sufficient to alter some developmental restrictions regulated by the epigenetic system. In this study, using pharmacological agents that interfere with the main components of the epigenetic program such as DNA methylation and histone deacetylation, we induce high-level expression of embryonic and neural stem cell (NSC) marker Sox2 in bone marrow-derived mesenchymal stem cells (MSCs). Exposure of these modified cells to a neural environment via juxtacrine and paracrine interactions promote efficient generation of neural stem-like cells as well as cells with neuronal and glial characteristics. We concluded that the manipulation strategy used in this study can be a useful method for efficient production of NSC-like cells from MSCs. 相似文献
953.
Annette Heisswolf Dirk Gabler Elisabeth Obermaier Caroline Müller 《Journal of Insect Behavior》2007,20(2):247-266
The importance of olfactory versus contact cues for host plant recognition was investigated in the tortoise beetle Cassida
canaliculata Laich. (Coleoptera: Chrysomelidae), which is strictly monophagous on meadow sage. The reaction of adult beetles
to olfactory and contact host cues was tested using three bioassays (locomotion compensator, six-chamber-olfactometer, ‘stem
arena’) to account for different behavioral contexts. Bioassay-guided fractionation of plant extracts was elaborated to characterize
the nature of contact stimuli. The beetles were only slightly attracted to odors from small amounts of leaf material. However,
when contact cues were provided additionally, the beetles showed strong preferences for samples of their host plant over controls.
Bioassay-guided fractionation led to isolation of at least two non-polar contact stimuli acting in concert that are sufficient
for host plant identification in C. canaliculata. 相似文献
954.
Longitudinal data on telomere length in leukocytes from newborn baboons support a marked drop in stem cell turnover around 1 year of age 总被引:1,自引:0,他引:1
Stem cells of various tissues are typically defined as multipotent cells with 'self-renewal' properties. Despite the increasing interest in stem cells, surprisingly little is known about the number of times stem cells can or do divide over a lifetime. Based on telomere-length measurements of hematopoietic cells, we previously proposed that the self-renewal capacity of hematopoietic stem cells is limited by progressive telomere attrition and that such cells divide very rapidly during the first year of life. Recent studies of patients with aplastic anemia resulting from inherited mutations in telomerase genes support the notion that the replicative potential of hematopoietic stem cells is directly related to telomere length, which is indirectly related to telomerase levels. To revisit conclusions about stem cell turnover based on cross-sectional studies of telomere length, we performed a longitudinal study of telomere length in leukocytes from newborn baboons. All four individual animals studied showed a rapid decline in telomere length (approximately 2-3 kb) in granulocytes and lymphocytes in the first year after birth. After 50-70 weeks the telomere length appeared to stabilize in all cell types. These observations suggest that hematopoietic stem cells, after an initial phase of rapid expansion, switch at around 1 year of age to a different functional mode characterized by a markedly decreased turnover rate. 相似文献
955.
Partridge L 《Aging cell》2007,6(5):595-598
The invertebrate model organisms continue to be engines of discovery in aging research. Recent work with Drosophila stem cells has thrown light on their human equivalents, and on the role of stem cells and their niches in the decline in fecundity with age. Inspired by observations of aging in bacteria and yeast, a new theoretical study has revealed evolutionary forces that could favour asymmetry in the distribution of damaged cell constituents at division, and hence pave the way for the evolution of aging and selective maintenance of integrity of the germ line. Mechanisms of nutrient sensing and cell signalling in the response of lifespan to dietary restriction have been elucidated. Powerful invertebrate models of human aging-related disease have been produced, and used to start to understand how the aging process acts as a risk factor for disease. In the near future, studies of invertebrate aging are likely to move away from an exclusive reliance on genetic manipulation towards a more biochemical and physiological understanding of these systems. 相似文献
956.
The extraembryonic endoderm of the elongating ovine conceptus was analyzed by scanning and transmission electron microscopy and by whole mount actin staining and immunofluorescence. Morphological and functional differences between the visceral endoderm (VE), the founding cell layer, and the parietal endoderm (PE) are presented. During the elongation process, the PE differentiated to fusiform multinucleated cells aligned parallel to the elongation axis of the conceptus, whereas the VE cells retained the aspect of typical epithelial cells. The multinucleated PE cells however, expressed cellular and nuclear markers typical of endodermal and polarized epithelial cells. The proteins of the extracellular matrix, laminin, and fibronectin, were specifically expressed in the PE. The presence of pairs of nuclei linked by mid-bodies positively stained with tubulin antibodies, indicated that the syncytial differentiation of the PE was due to karyokinesis which was not followed by cytokinesis rather than by cell fusion. 相似文献
957.
958.
Null mutations in the Drosophila gene, slowmo (slmo), result in reduced mobility and lethality in first-instar larvae. Slowmo encodes a mitochondrial protein of unknown function, as do the two other homologs found in Drosophila. Here, we have studied a hypomorphic P-element allele of slmo demonstrating its effects on germline divisions in both testes and ovaries. Using in situ studies, enhancer-trap activity, and promoter fusions, we have shown that slmo expression in testes is found in the somatic cyst cells (SCC). The hypomorphic allele for Slmo revealed apoptotic loss of germline cells in the larval germline, culminating in a complete absence of the germline in adult flies. In females, a similar degeneration of the germarium is observed, while reporter gene expression is found in both germline and somatic cells. Using a null mutation in female germline clones, we find slmo is dispensable from the germline cells. Our results suggest that Slowmo is not required in germline cells directly, but is required in SCCs responsible for maintaining germline survival in both sexes. 相似文献
959.
Mohammed I. Al-Daej Mohamed M. El-Malky Muhammad N. Sattar Adel A. Rezk Muhammad N. Naqqash Jameel M. Al-Khayri 《Phyton》2022,91(9):1905-1922
Rice stem borer (Chilo agamemnon Bles.) is a primary insect pest of rice and is a major limiting factor to rice
production. Breeding for insect-resistant crop varieties has been an economic way of integrated pest management
(IPM) as it offers a viable and ecologically acceptable approach. This study was aimed to evaluate rice genotypes
for their resistance against rice stem borer. Seven parental genotypes with twenty one F1 crosses were evaluated
for genotypic variation in field experiments. Analysis of variance revealed significant differences for the studied
traits in almost all crosses and parents. In addition, the mean squares of parents versus their crosses were signifi-
cant for stem borer resistance and other associated traits. Moreover, both general combining ability (GCA) and
specific combining ability (SCA) variances were highly significant for all characters studied in the F1 generation.
Based on GCA, 4 genotypes (Sakha101, Gz6903-3-4-2-1, Gz9577-4-1-1 and Hassawi) exhibited highly significant
negative values for stem borer resistance (–0.53, –1.06, –0.18 and –0.49, respectively) indicating they are the best
combiners for stem borer resistance. Based on SCA analysis, nine cross combinations showed highly significant
negative effects for stem borer resistance. Similarly, the cross Giza178 Hassawi was the best combination with
significantly highest value for early maturity. In addition, seven crosses showed highly significant negative
SCA for plant height trait. On the other hand, for panicle length, number of primary branches/panicle, panicle
weight and 1000-grain weight, seven, four, eight and six crosses showed highly significant positive SCA, respectively. The result further revealed that the non-additive dominance genetic variance was higher than the additive
variance for all evaluated traits indicating that non-additive genetic variances have a role in their inheritance. The
broad-sense heritability estimates were high for all the studied traits. The stem borer resistance was significantly
correlated with panicle weight and 1000-grain weight, which also showed a highly significant correlation with
grain yield/plant. Thus these traits can be effectively employed in a breeding program to confer resistance against
stem borer infestation in rice. It was further supported by biplot analysis, which clustered these potentially important traits into two quadrants showing their importance in any future breeding program to control stem borer
infestation. This study has contributed valuable information for evaluation of genetic diversity in the local rice
germplasm and its utilization in futuristic rice genetic improvement programs. 相似文献
960.
Kaisa Rissanen Juho Aalto Arthur Gessler Teemu Hltt Andreas Rigling Marcus Schaub Jaana Bck 《Plant, cell & environment》2022,45(1):23-40
Tree stems have been identified as sources of volatile organic compounds (VOCs) that play important roles in tree defence and atmospheric chemistry. Yet, we lack understanding on the magnitude and environmental drivers of stem VOC emissions in various forest ecosystems. Due to the increasing importance of extreme drought, we studied drought effects on the VOC emissions from mature Scots pine (Pinus sylvestris L.) stems. We measured monoterpenes, acetone, acetaldehyde and methanol emissions with custom-made stem chambers, online PTR-MS and adsorbent sampling in a drought-prone forest over the hot-dry summer of 2018 and compared the emission rates and dynamics between trees in naturally dry conditions and under long-term irrigation (drought release). The pine stems were significant monoterpene sources. The stem monoterpene emissions potentially originated from resin, based on their similar monoterpene spectra. The emission dynamics of all VOCs followed temperature at a daily scale, but monoterpene and acetaldehyde emission rates decreased nonlinearly with drought over the summer. Despite the dry conditions, large peaks of monoterpene, acetaldehyde and acetone emissions occurred in late summer potentially due to abiotic or biotic stressors. Our results highlight the potential importance of stem emissions in the ecosystem VOC budget, encouraging further studies in diverse environments. 相似文献