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1.
Leah Edelstein 《Differentiation; research in biological diversity》1982,23(1-3):1-9
Abstract. The selection of polarity in cells of the cambium in higher plants is a regulated process of development which results in horizontally or vertically oriented cells. A set of mathematical equations suggestive of this developmental dichotomy is given a new biologic interpretation. As a result, a molecular scheme capable of acting as a biochemical switch is suggested. The model features two structural protein monomers whose synthesis is controlled autogenously by feedback repression. The implications of this and similar mechanisms to other differentiating systems is discussed. 相似文献
2.
Extracellular protein secretion by the main terminal branch of the general secretory pathway in Pseudomonas aeruginosa requires a secretion machinery comprising the products of at least 12 genes. One of the components of this machinery, the XcpR protein, belongs to a large family of related proteins distinguished by the presence of a highly conserved nucleotide binding domain (Walker box A). The XcpR protein is essential for the process of extracellular secretion and amino acid substitutions within the Walker A sequence result in inactive XcpR. The same mutations exert a dominant negative effect on protein secretion when expressed in wild-type bacteria. Transdominance of XcpR mutants suggests that this protein is involved in interactions with other components of the secretion machinery or that it functions as a multimer. In this study, the amino-terminal portion of the cI repressor protein of phage λ was used as a reporter of dimerization in Escherichia coli following fusion to full-length as well as a truncated form of XcpR. The cI–XcpR hybrid proteins were able to dimerize, as demonstrated by the immunity of bacteria expressing them to killing by λ phage. The full-length XcpR as well as several deletion mutants of XcpR were able to disrupt the dimerization of the chimeric cI–XcpR protein. The disruption of cI–XcpR dimers using the deletion mutants of XcpR, combined with the analysis of their dominant negative effects on protein secretion, was used to map the minimal dimerization domain of XcpR, which is located within an 85 amino acid region in its N-terminal domain. Taken together, the data presented in this paper suggest that the XcpR protein dimerizes via its N-terminus and that this dimerization is essential for extracellular protein secretion. 相似文献
3.
Kinetic continuum models are derived for cells that crawl over a 2D substrate, undergo random reorientation, and turn in response to contact with a neighbor. The integro-partial differential equations account for changes in the distribution of orientations in the population. It is found that behavior depends on parameters such as total mass, random motility, adherence, and sloughing rates, as well as on broad aspects of the contact response. Linear stability analysis, and numerical, and cellular automata simulations reveal that as parameters are varied, a bifurcation leads to loss of stability of a uniform (isotropic) steady state, in favor of an (anisotropic) patterned state in which cells are aligned in parallel arrays. 相似文献
4.
A model for growth of a tissue culture consisting of cell clumps is given. A set of equations for following the size distribution of clumps is used to determine total biomass accumulation. Existence and uniqueness of a solution to the equations is proved, and estimates of the biomass growth is given in a number of situations. 相似文献
5.
James M. Berger Paul J. Jackson Nigel J. Robinson Leah D. Lujan Emmanuel Delhaize 《Plant cell reports》1989,7(8):632-635
Suspension cultures of Datura innoxia cells were pulse-labeled with [35S]cysteine, then exposed to Cd to determine whether there is a direct precursor-product relationship amongst the different forms of the Cd-induced polypeptides, poly(-glutamylcysteinyl)glycines [(EC)nG, n=2 to 5]. Degradation of the polypeptides and possible regeneration of the [35S]-labeled glutathione and cysteine pools were also examined. After 2 h of exposure to [35S]cysteine, about 70% of the [35S]cysteine in the soluble fraction of the cell was incorporated into [35S]glutathione before exposure of the cells to Cd. One h after Cd exposure, most of the cellular [35S]glutathione was depleted and label was incorporated into (EC)nG. Analysis of [35S](EC)nG by reverse phase HPLC showed no direct precursor-product relationship between the synthesis of the shorter and longer chain forms. However, the rate of synthesis of the different polypeptides was linear for 32 h after Cd exposure. There was no evidence of degradation of [35S](EC)nG nor was it excreted into the medium within this period. From these results it is suggested that in the presence of Cd, a large pool of (EC)nG is unavailable for elongation to (EC)n+1G.Abbreviations (EC)nG
Poly(-glutamylcysteinyl)glycine
- HPLC
High pressure liquid chromatography
- CPM
Counts per minute 相似文献
6.
Conclusions By the time George Wilton Field concluded his work at the marine laboratory his initial scientific concerns had forced him directly into local politics. He pleaded with little success with the community of South Kingstown, and with no success with the town of Narragansett, to create and maintain a permanent breach:Is it not possible for the acute business sense and the broad philanthropy of the community to sweep aside petty, local, and personal jealousies which are now blocking practical progress for the establishment of a permanent breach at Point Judith Pond? It is truly criminal neglect which permits fifteen hundred acres of valuable water-farming area to lie practically idle and rapidly deteriorate with each passing year.... In the opinion of the writer the Point Judith Pond and those of similar type could be made the seat of oyster, clam, crab, herring, white perch, and striped bass fisheries.30
In the summer of 1899 Field was invited to teach a summer course on echinoderms at the MBL in Woods Hole, and to conduct summer research in a laboratory of the U.S. Fish Commission, also located at Woods Hole. When the summer was over, he remained there. Whether he had intentions of returning to resume his position in Rhode Island is unclear. At this point all correspondence with the Agricultural Experiment Station ceases, and Field's last report is a brief statement in the annual report of the experiment station for 1900 wherein he laments the variety of experiments he has not been able to carry to conclusion, such as a study of the artificial fertilization of water analogous to the method of chemically fertilizing the land for crops.The correspondence reveals that the enthusiasm Field brought to Point Judith Pond in 1896 was gradually sapped by his own fragile health, by three years' exposure to the local politics surrounding the southern Rhode Island fishing industry, and by a college administration determined to remove the stench of his invertebrates. He sought a refuge in the sheltered world of pure research at the U.S. Fish Commission Laboratory, where he set out to investigate the Origin of Sex using, as his animal models, squid and toadfish.On November 14, 1899, the Board of Managers of the college ordered the director of the experiment station to dispose of the marine laboratory at Point Judith Pond.31 How long the laboratory at Buttonwood Point survived in the institutional memory of the University of Rhode Island is open to question. The current Graduate School of Oceanography, in the event, traces its history back to 1937, not 1896.Nevertheless, Field and his one-room marine station established a precedent of land-grant marine research that other state colleges would follow, including Rhode Island itself, which reestablished its marine station, this time permanently, at South Ferry in 1937. In his brief research career in Rhode Island, George Wilton Field had discovered the same coastal attributes that would lead later to the creation of one of the world's major marine research centers at the University of Rhode Island's Graduate School of Oceanography.And, in a measure of triumph for his work, little more than a year after Field left for Woods Hole and his laboratory was dismantled, the town of South Kingstown voted the funds necessary to begin the construction of a permanent breachway.32 Whether Field's scientific reasoning and the conclusions of his marine research played any part in finally deciding the thirty-year-old debate in the affirmative will probably never be known. What is evident is that Field had no patience for those who could not see the results of his research as clearly as he could himself. 相似文献
7.
8.
We analyse the helical motion of organisms, concentrating on the means by which organisms change the direction in space of
the axis of the helical trajectory, which is the net direction of motion. We demonstrate that the direction of the axis is
determined largely by the direction of the organism's rotational velocity. Changes in direction of the rotational velocity,
with respect to the organism's body, change the direction in space of the axis of the helical trajectory. Conversely, changes
in direction of the translational velocity, with respect to the body of the organism, have little effect on the direction
in space of the axis of the trajectory. Because the axis of helical motion is the net direction of motion, it is likely that
organisms that move in helices change direction by pointing their rotational velocity, not their translational velocity, in
a new direction. 相似文献
9.
Niraj Shrestha Pallavi Chaturvedi Xiaoyun Zhu Michael J. Dee Varghese George Christopher Janney Jack O. Egan Bai Liu Mark Foster Lynne Marsala Pamela Wong Celia C. Cubitt Jennifer A. Foltz Jennifer Tran Timothy Schappe Karin Hsiao Gilles M. Leclerc Lijing You Christian Echeverri Catherine Spanoudis Ana Carvalho Leah Kanakaraj Crystal Gilkes Nicole Encalada Lin Kong Meng Wang Byron Fang Zheng Wang Jin-an Jiao Gabriela J. Muniz Emily K. Jeng Nicole Valdivieso Liying Li Richard Deth Melissa M. Berrien-Elliott Todd A. Fehniger Peter R. Rhode Hing C. Wong 《Aging cell》2023,22(5):e13806
10.
Peleg Leah Nesbitt Muriel N. Ashkenazi Israel E. 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1982,147(1):137-142
Journal of Comparative Physiology A - A/J mice differ from C57BL/6J mice in the time of the daily peak of activity of glyceraldehyde-3-phosphate dehydrogenase (GAPD) in thymus and in thyroid.... 相似文献