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1.
Gametes of the unicellular green alga Chlamydomonas reinhardii recognize and adhere to cells of the opposite mating type by flagellar contact. Adhesion between these specialized organelles signals a rapid series of mating events which result in gamete fusion. The sequence of morphological changes (flagellar tip activation, cell wall loss, and mating structure elongation), which occur as a consequence of the sexual signalling, have been characterized. The signalling mechanisms have, however, not been defined. Calcium is known to be involved during fertilization of animal species. Increased intracellular free calcium, which can be achieved either by calcium influx or by mobilization of ions from intracellular stores, has been observed during activation of both eggs and sperm. A recent report by Bloodgood & Levin that gametes of C. reinhardii preloaded with 45Ca showed a transient increase in Ca efflux following mating, suggests that intracellular Ca redistribution may also accompany mating in this algal species. We have used X-ray microanalysis to analyze the subcellular distribution of bound calcium during mating in Chlamydomonas reinhardii. X-ray maps reveal that calcium is sequestered in discrete granules within the gamete cell body prior to mating and that during activation and cell fusion, calcium is diffuse throughout the cell. This suggests the possibility that calcium serves as a second messenger in this species. 相似文献
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Gwenvael Le Dréau Murielle Saade Irene Gutiérrez-Vallejo Elisa Martí 《The Journal of cell biology》2014,204(4):591-605
The different modes of stem cell division are tightly regulated to balance growth and differentiation during organ development and homeostasis. However, the mechanisms controlling such events are not fully understood. We have developed markers that provide the single cell resolution necessary to identify the three modes of division occurring in a developing nervous system: self-expanding, self-renewing, and self-consuming. Characterizing these three modes of division during interneuron generation in the developing chick spinal cord, we demonstrated that they correlate to different levels of activity of the canonical bone morphogenetic protein effectors SMAD1/5. Functional in vivo experiments showed that the premature neuronal differentiation and changes in cell cycle parameters caused by SMAD1/5 inhibition were preceded by a reduction of self-expanding divisions in favor of self-consuming divisions. Conversely, SMAD1/5 gain of function promoted self-expanding divisions. Together, these results lead us to propose that the strength of SMAD1/5 activity dictates the mode of stem cell division during spinal interneuron generation. 相似文献
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We have used the HLA-C-specific DNA probe pC250 to investigate restriction fragment length polymorphism (RFLP) at the HLA-C locus. Genomic Southern blot hybridization included DNA prepared from a panel of homozygous typing cells representing serological specificities Cw1 to Cw8 and also from samples representing Cw blanks. Although many restriction nucleases failed to reveal any polymorphism, RFLPs were evident with Taq I, Pvu II, Bst XI, Nde 1, and Nci I in addition to the previously reported Eco RI. In the case of Bst XI, a unique RFLP defined a subset of serologically defined Cw blanks. Comparison of RFLP sizes with restriction fragment lengths obtained from the known HLA-Cw3 gene sequence permitted the localization of intragenic C locus RFLLs and the identification of a variable Taq I site in the second intron, a variable Nci I site near the end of the fourth exon, and a variable Pvu lI site in the fifth intron. 相似文献
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The accumulation of mature RNA for the Xenopus laevis ribosomal protein L1 is controlled at the level of splicing and turnover of the precursor RNA. 总被引:17,自引:5,他引:12 下载免费PDF全文
A specific control regulates, at the level of RNA splicing, the expression of the L1 ribosomal protein gene in Xenopus laevis. Under particular conditions, which can be summarized as an excess of free L1 protein, a precursor RNA which still contains two of the nine introns of the L1 gene accumulates. In addition to the splicing block the two intron regions undergo specific endonucleolytic cleavages which produce abortive truncated molecules. The accumulation of mature L1 RNA therefore results from the regulation of the nuclear stability of its precursor RNA. We propose that a block to splicing can permit the attack of specific intron regions by nucleases which destabilize the pre-mRNA in the nucleus. Therefore the efficiency of splicing could indirectly control the stability of the pre-mRNA. 相似文献
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Scott T. Sayers Hock C. Yeoh Jerry A. McLane Irene R. Held 《Neurochemical research》1988,13(12):1125-1131
The acetylcholine receptor (AChR) content and the autorphosphorylation of the regulatory subunit of cyclic AMP-dependent protein kinase type II (R-II) were evaluated in rat soleus muscles at 24, 30 and 66 hr after surgical denervation by cutting the nerve at a short distance (short-nerve-stump) and at a long distance (long-nerve-stump) from the muscle. AChR content was based on the specific binding of [125I]alpha-bungarotoxin (BUTX); changes in the autophosphorylation of R-II were based upon the predominant in vitro32P-phosphorylation of a 56-Kd soluble protein in cytosolic fractions of solei. The AChR content and the32P-autophosphorylation of R-II were increased in samples from short-nerve-stump solei, but not from long-nerve-stump solei, after a denervation-time of 30 hr. This nerve-stump-length dependency indicates that the two denervation effects are not related to the immediate halt of impulse-evoked muscle contractility. Furthermore, the results show that alterations in the32P-autophosphorylation of R-II occurred before, as well as whenever, increases in the AChR content were found. Speculatively, this temporal relationship may be significant with respect to the potential role of R-II in gene expression.Abbreviations ACh
acetylcholine
- AChR
acetylcholine receptor(s)
- BUTX
alpha-bungarotoxin
- Kd
kilodalton
- PAGE
polyacrylamide gel electrophoresis
- R-II
regulatory subunit of cyclic AMP-dependent protein kinase type II
- SDS
sodium dodecyl sulfate 相似文献