Formation of Hassall's corpuscles in vitro by the thymic epithelial cell line IT-26 R 21 of the rat

Summary In the monolayer of an established epithelial cell line from the rat thymus, IT-26R21, characteristic cell aggregates quite similar to Hassall's corpuscles were formed. These aggregates were examined by light and electron microscopy, and immunohistochemically. Their interpretation as Hassall's corpuscles is based on the following observations: (1) The aggregates are formed in the monolayer of cells that greatly resemble medullary epithelial cells of the thymus. (2) They consist of flattened epithelial cells in a concentric pattern with one or more degenerating cells in the center. (3) Loss of microvilli suggests that these cells are keratinizing. (4) The aggregates show strongly positive reactions in immunofluorescent staining with antikeratin and antiprekeratin.When Hassall's corpuscles increase in size, cellular proliferation is somewhat suppressed. Both in vivo and in vitro, they may be interpreted as an expression of a changing growth pattern in confined spaces and thus seem to have little immunological function.     

Cell wall turnover in phosphate and potassium limited chemostat cultures of Bacillus subtilis W23

Turnover in phosphate and potassium limited chemostat cultures of Bacillus subtilis W23 results in the release of over 80% of the wall material present at the time of chasing equilibrium-labelled cultures. The rate at which turnover proceeds is faster in potassium limited cultures than in phosphate limited cultures but in both cases a fraction of the wall material appears to be conserved, or to undergo turnover at a lower rate. Previously we have shown that the polar wall is less active metabolically than the cylindrical wall and it is possible that the apparently conserved wall is that present in the pole.     

Cell cycle inHelianthus tuberosus tuber tissue in relation to dormancy

Summary Observations are presented on the patterns of DNA synthesis and mitotic activity in medullary parenchyma cells excised from tubers ofHelianthus tuberosus in four different periods of dormancy. Dormancy break (activation) was induced byin vitro culture on media added with 2,4-dichlorophenoxyacetic acid. The cell cycle responsein vitro to different combinations of growth substances has also been investigated.The results show that remarkable changes in the timing of the first and second cell cycles and their phases occur with the progression of dormancy. With increasing time after tuber harvest, the following behaviours are observed: (i) a lengthening of the first cell cycle, chiefly due to a lengthening of the G₂ phase (G₂ is absent at the beginning of dormancy) and an increase in the time interval between the start of thein vitro culture and the onset of the first mitotic wave; (ii) an increased duration of the S phase; (iii) a remarkable reduction in the cell synchrony.These behaviours, as indicated also by their comparison with thein vitro response of the cell cycle to different hormonal treatments, seem to depend on the physiological status of the tubers at the time of explant. It is concluded that the analysis of the cell cycle is an useful tool for understanding some aspects of such a complex physiological situation as dormancy.Istituto di Mutagenesi e Differenziamento del C.N.R., Pisa, Italy, publication no. 321.     

The extinction of slowly evolving dynamical systems

The time evolution of slowly evolving discrete dynamical systems x _{i + 1} = T(r _i ,x _i ), defined on an interval [0, L], where a parameter r _ichanges slowly with respect to i is considered. For certain transformations T, once r _i reaches a critical value the system faces a non-zero probability of extinction because some x _j [0, L]. Recent ergodic theory results of Ruelle, Pianigiani, and Lasota and Yorke are used to derive a simple expression for the probability of survival of these systems. The extinction process is illustrated with two examples. One is the quadratic map, T(r, x) = rx(1 – x), and the second is a simple model for the growth of a cellular population. The survival statistics for chronic myelogenous leukemia patients are discussed in light of these extinction processes. Two other dynamical processes of biological importance, to which our results are applicable, are mentioned.     

Scanning and transmission electron microscopy of the squamose gill-filament epithelium from fresh- and seawater adaptedTilapia

Synopsis The architecture of the gill structure of variousTilapia species was studied in relation to their adaptability to hypersaline media. Using SEM and EM, it was shown that the squamose epithelial cells of the gills have species-typical patterns of ridges on their outer surfaces. These have previously been misinterpreted by other authors as microvilli or stereocillia. The ridges are more dense and better developed in euryhaline species, likeT. zillii, and less so in stenohaline species likeSarotherodon niloticus. Comparing freshwater and seawater-adapted individuals ofT. zillii, S. niloticus, S. galflaeus, andTristramella sacra, it was shown that in fresh water the surface cells are slightly swollen, extending over the openings of the chloride cells. During adaptation to sea water, these ridges become higher and denser and the cell surface shrinks, exposing the underlying orifices of the apical crypts of the chloride cells. The more euryhaline the species, the less change there is in the ridge pattern of the cells during passage from fresh to sea water. This evidence implicates the gill epithelium, together with the chloride cells, in the process of osmoregulation.     

Correlation between cell density,membrane fluidity,and the availability of transferrin receptors in friend erythroleukemic cells

Undifferentiated Friend erythroleukemic cells (FL cells) acquire membrane microviscosity ( ), in accord with the culture cell density. At low cell density poise, whereas at confluency it increases to poise. Concomitantly, the total number of available transferrin receptors per cell decreases by about 80% upon increase in cell density. Modulation of membrane microviscosity, by artificial alteration of the membrane cholesterol level, mediates similar modulations of the availability of the transferrin receptors. The correlation between the availability of the transferrin receptors and the membrane lipid fluidity may take part in the overt decrease in iron uptake by erythroid cells along the erythropoiesis pathway.     

Relations between water content, potential and permeability in stems of conifers

Abstract. The influence of sapwood water content on the conductivity of sapwood to water was measured on stem sections of Pinus contorta. A reduction in relative water content from 100 to 90% caused permeability to fall to about 10% of the saturated value.
Pressure–volume curves of branchwood and stem sapwood of Pinus contorta and Picea sitchensis have been analysed to definè the tissue capacitance and the time constant and resistance for water movement between stored water and the functional xylem as functions of tissue water potential. Three phases in water loss were discernible. In the initial phase at high water potentials (> –0.5 MPa), the capacitance was large, the time constant long and the resistance to flow large in comparison with intermediate water potentials (−0.5 to −1.5 MPa). At still lower water potentials (−1.5 to −3.0 MPa), the time constant and resistance declined still further but the capacitance had a tendency to increase again, especially in the stemwood of Sitka spruce. Typical values in the second phase were for the time constant 5 s, for the resistance 4 × 10⁻¹³ N s m⁻⁵ and for the capacitance (change in relative water content per unit change in potential) 1×10⁻¹¹ m³ Pa⁻¹. These parameters define the availability of stored water and are being used in a dynamic model of water transport in trees.     

Brugia pahangi: Feeding and nutrient uptake in vitro and in vivo

Incubation in vitro of adult Brugia pahangi in an apparatus which permitted the separate exposure of the anterior, middle, or posterior region of the worms to medium-containing radioactively labeled d-glucose, l-leucine, and adenosine has provided evidence that these materials are taken up in physiologically significant amounts by a transcuticular route. No evidence for an oral ingestion of materials has been obtained from worms in vitro, but in vivo an oral uptake of Trypan blue has been demonstrated. The ultrastructure and cytochemical staining reactions for nonspecific esterase, acid phosphatase (EC-3.1.3.2), and leucine naphthylamidase of the gut and body wall are described.