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Abstract. The position-dependent mitotic index before, and 1, 2 and 3 h after vincristine was scored. the accumulation of cells in mitosis leads to an increase in the mitotic index from 0.06 to 0.34 at crypt positions 8-12. Surprisingly, the leading edge of the position-related mitotic index distribution moves to higher crypt positions although cell division was stopped. In addition, the vertical clustering of mitotic figures in sections was recorded. the data were examined using a previously described computer crypt model. We conclude: the average mitotic phase duration is about 0.7 h (40 min) and varies little with cell position; the geometrical correction factor for overscoring mitoses in crypt sections is about 0.6-0.7 and adjacent cell columns can merge. Lateral cell displacement after mitosis, as predicted in a previous model analysis, would be a mechanism to counteract other forces that tend to reduce the crypt circumference. In the normal steady state merging and expansion processes would just balance each other. This would not follow if one mechanism was blocked. Thus we propose a new concept in which the crypt geometry would be dynamically determined by cell proliferative activity in connection with lateral positioning of new cells on one hand and contracting forces on the other hand. 相似文献
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C S Potten S A Roberts S Chwalinski M Loeffler U Paulus 《Cell and tissue kinetics》1988,21(4):231-246
Various counts have been made of the number of mitotic figures in whole crypts and sections of crypts of the small intestine of the mouse. Samples were analysed from animals killed at different times of the day and at different times after administration of vincristine. Measurements have been made of the size of mitotic and interphase nuclei and of the radial position of mitotic figures. The correction factor, f, which is required to take into account the enhancement of mitotic counts in sections as a consequence of their centripetal position has been investigated. The results indicate the following: (1) transverse sections of the crypt differ from longitudinal sections if they involve cutting the intestine before fixation which may result in a relaxation of the crypt and its widening by 25%; (2) columnar cell nuclei have a shape that resembles a sphere flattened so that the average diameter is 20% greater in crypt transverse sections; (3) mitotic nuclei tend to be about half-way between the crypt edge and the central axis of the crypt; (4) between about four and seven times more mitotic figures have their mitotic axis parallel to the long axis of the crypt; (5) about one-third of all mitotic figures in a crypt are seen in a longitudinal section of the crypt. If this is related to the number of cells in the crypt as a whole and in a section, a correction factor fD for the mitotic index of 0.59 is obtained; (6) the correction factor fT derived from the shape and position of the mitotic figures measured in 3 microns longitudinal sections is 0.53; (7) relating cell cycle and mitotic accumulation data using a computer-based model of the crypt also permits a correction factor fmod to be estimated. This gives a value of 0.66. When sectioned material is used to calculate a mitotic index the most appropriate correction factor is fD; for mouse small intestine it is 0.59. 相似文献
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Chronic arthropathy occurring after augmentation mammaplasty 总被引:1,自引:0,他引:1
Augmentation mammaplasty has been associated with a broad spectrum of connective-tissue disease, systemic illness and autoimmune phenomena. The three cases reported herein suggest a possible relationship between silicone gel implants for augmentation mammaplasty (with capsular contractures as complicating feature) and the development of chronic arthropathy. 相似文献
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Brigitte Huss Bruno Tinland François Paulus Bernard Walter Léon Otten 《Plant molecular biology》1990,14(2):173-186
The ubiquitous grapevine-associated octopine/cucumopine Ti plasmids of biotype III Agrobacterium tumefaciens strains carry two T regions, TA and TB, with a complex oncogene arrangement. Within the octopine/cucumopine group, two main strain types were identified: large TA strains with a TA region resembling the TL region of the biotype I octopine strain Ach5 and small TA strains with a similar T region organization as the large TA strains but with a large internal TA deletion. Structural and functional studies of the representative large TA strain Tm4 revealed six oncogenes. Each oncogene was inserted in a disarmed vector and tested for biological activity using the corresponding oncogenes of Ach5 as standards. Five Tm4 oncogenes, TA-iaaM, T-ipt, T-6b, TB-iaaH and TB-iaaM, were shown to be active, the IS-interrupted TA-iaaH gene was inactive. To study the role of each gene in the pTiTm4 context, several single and multiple pTiTm4 mutations were constructed. It was shown that whereas TA-iaaM and TB-iaaH are essential for tumour formation on grapevine, T-ipt, T-6b and TB-iaaM are not. The avirulence of the TA-iaaM
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mutant was shown to be due to an inhibitory effect of the T-ipt gene, since a TA-iaaM
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/T-ipt
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double mutant was fully virulent. We conclude that the TA-iaaM gene of large TA strains is specifically required to counteract the tumour growth inhibiting activity of the T-ipt gene. Both TA-iaaM and T-ipt are absent from the small TA strains. A model on the roles and interactions of the different oncogenes in large TA and small TA strains is presented. 相似文献
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Abstract The stemmata of last–instar Nannochoristalarvae are compound eyes composed of 10 or more ommatidia. Each ommatidium has four Semper cells, four distal and four proximal retinula cells which form a cruciform and layered rhabdom. The ommatidia are separated by epidermal cells (possibly rudimentary pigment cells). Corneal lenses are lacking. At the posterior edge, aberrant stemma units may be present which lack a dioptric apparatus and have a star–shaped rhabdom composed of at least six retinula cells. The stemmata of Nannochoristaappear to be derived from stemmata of the Panorpa-type (Mecoptera-Panorpidae). Differences between the stemmata of Nannochoristaand Panorpacan be explained as adaptations to aquatic life (flat cornea) or as regression. A compound larval eye is ascribed to the ground plan of the Mecoptera sensu latoand is considered a genuine plesiomorphy. The identical basic number (seven) of stemmata in the Neuropteroid/Coleoptera assemblage, Amphiesmenoptera and some Mecoptera (Bittacidae, Boreidae) is attributed to parallel evolution. 相似文献
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Desensitization of Bacillus subtilis aspartokinase I to allosteric inhibition by meso-diaminopimelate allows aspartokinase I to function in amino acid biosynthesis during exponential growth. 总被引:1,自引:0,他引:1
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Strains of Bacillus subtilis deficient in aspartokinases II and III are unable to grow in the absence of lysine, methionine, and threonine, although they have normal levels of aspartokinase I (J.J. Zhang, F.M. Hu, N.Y. Chen, and H. Paulus, J. Bacteriol. 172:701-708, 1990). Revertants with the ability to grow in the absence of lysine and methionine had an altered aspartokinase I, which was insensitive to feedback inhibition by meso-diaminopimelate. This suggests that inhibition by meso-diaminopimelate limits the ability of aspartokinase I to function in amino acid biosynthesis. 相似文献
10.
Synthesis and inactivation of carbamyl phosphate synthetase isozymes of Bacillus subtilis during growth and sporulation.
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Pyrimidine-repressible carbamyl phosphate synthetase P was synthesized in parallel with aspartate transcarbamylase during growth of Bacillus subtilis on glucose-nutrient broth. Both enzymes were inactivated at the end of exponential growth, but at different rates and by different mechanisms. Unlike the inactivation of aspartate transcarbamylase, the inactivation of carbamyl phosphate synthetase P was not interrupted by deprivation for oxygen or in a tricarboxylic acid cycle mutant. The arginine-repressible isozyme carbamyl phosphate synthetase A was synthesized in parallel with ornithine transcarbamylase during the stationary phase under these growth conditions. Again, both enzymes were subsequently inactivated, but at different rates and by apparently different mechanisms. The inactivation of carbamyl phosphate synthetase A was not affected in a protease-deficient mutatn the inactivation of ornithine transcarbamylase was greatly slowed. 相似文献