Morphogenesis by symbiogenesis.

Here we review cases where initiation of morphogenesis, including the differentiation of specialized cells and tissues, has clearly evolved due to cyclical symbiont integration. For reasons of space, our examples are drawn chiefly from the plant, fungal and bacterial kingdoms. Partners live in symbioses and show unique morphological specializations that result when they directly and cyclically interact. We include here brief citations to relevant literature where plant, bacterial or fungal partners alternate independent with entirely integrated living. The independent, or at least physically unassociated stages, are correlated with the appearance of distinctive morphologies that can be traced to the simultaneous presence and strong interaction of the plant with individuals that represent different taxa.     

Theoretical studies of protein conformation by means of energy computations

In this review we describe fundamental concepts and applications of conformational energy computations, with emphasis on some recent advances and problems being investigated. The formulation of potential energy functions is described, including the nature of the intramolecular force field, the representation of interactions with the solvent, and considerations of entropy contributions. Approaches to the search for the optimal potential energy are summarized. Examples cited among applications of conformational energy computations include refinement of X-ray crystallographic structures, the use of computations in conjunction with NMR data, prediction of the structures of proteins based on either homology or on other procedures that surmount the multiple-minima problem, the analysis of hierarchical levels of structure and assembly, and interactions in enzyme-substrate complexes.     

Induction of DNA double strand breaks by arsenite: comparative studies with DNA breaks induced by X-rays

Chinese hamster ovary (CHO-K1) cell line and two of its DNA double strand break (DSB) repair deficient mutant cell lines, xrs-5 (Ku80 mutant) and irs-20 (DNA-PKcs mutant), were treated with various concentrations of sodium arsenite for 2.5h, and the colony forming abilities were studied. The wild type cells showed the highest cell survival, while xrs-5 cells showed the lowest survival, and irs-20 cells had an intermediate survival. These results are very similar to the cell survival curves induced by X-rays in these three cell lines. Our data also show the dose dependent induction of DNA-DSBs in these cell lines exposed to arsenite. However, in order to obtain a similar cell survival in wild type cells, twice as many DNA-DSBs are necessary with arsenite exposure when compared with X-rays, suggesting that the types of DNA lesions leading to DSB induced by arsenite are different from those by X-rays. Based on these data, further mechanistic investigations including the involvement of DNA-DSB repair proteins are warranted in the recovery process from arsenic (As) exposure.     

Sensitization to heat by X-rays

1. Paramecium caudatum is sensitized to heat by sublethal dosages of x-rays. Thus if paramecia are irradiated, then exposed to a sublethal dosage of heat they are killed, but if the same heat exposure precedes the same dosage of radiations, they are not. 2. Sensitivity to both heat and x-rays is much greater in paramecia from the log growth phase than in those from the stationary phase of a culture. 3. Recovery from heat sensitization in animals from the stationary phase of a culture is slow, requiring several days. 4. Division is readily retarded and even temporarily inhibited by sublethal dosage of x-rays. Recovery of the division rate is fairly slow requiring several days. 5. Paramecia can be killed by a dosage of 1,200,000 r (of which about one-half reach the animal) units of x-radiation alone. Smaller dosages are not lethal if the paramecia are transferred to fresh medium immediately upon completion of irradiation. 6. The possibility of utilization of heat sensitization in treatment of malignant growths is discussed.     

Linkage studies of Friedreich ataxia by means of blood-group and protein markers

Friedreich ataxia (FA) is an autosomal recessive, neuro-degenerative disorder in which the pathogenetic mechanism remains unidentified despite extensive biochemical studies. Genetic-linkage studies provide an alternative approach to determining the basic defect. Linkage analysis between FA and 36 polymorphic-blood-group and protein markers has been carried out on three separate patient populations--16 families from the inbred Acadian population of Louisiana, 21 French-Canadian families from Quebec, and nine apparently unrelated British families--in an attempt to determine the chromosomal location of the disease mutation. Neither evidence of linkage to any of the markers investigated nor heterogeneity among the populations was found for any of the comparisons. The negative lod scores exclude the locus for FA from greater than 20% of the genome.     

Vitality studies in bone marrow cells by means of fluorescence microscopy]

In assessing the vitality of bone-marrow cells vital fluorochroming with acridine orange allows a differential, qualitative statement to be made about the degree of cell damage and in addition the single cell compartments to be relatively well differentiated in morphological respect. The stain exclusion test made for the purpose of comparison merely enables an approximate, quantitative evaluation to be obtained.     

The influence of X-rays on the structural studies of peroxide-derived myoglobin intermediates

In recent years, the awareness of potential radiation damage of metal centers in protein crystals during crystallographic data collection has received increasing attention. The radiation damage can lead to radiation-induced changes and reduction of the metal sites. One of the research fields where these concerns have been comprehensively addressed is the study of the reaction intermediates of the heme peroxidase and oxygenase reaction cycles. For both the resting states and the high-valent intermediates, the X-rays used in the structure determination have given undesired side effects through radiation-induced changes to the trapped intermediates. However, X-rays have been used to generate and trap the peroxy/hydroperoxy state in crystals. In this review, the structural work and the influence of X-rays on these intermediates in myoglobin are summarized and viewed in light of analogous studies on similar intermediates in peroxidases and oxygenases.     

Prenatal pathogenesis of hydro-micrencephaly induced by X-rays

Summary Experimental results are presented which describe induction and pathogenesis of the hydro-micrencephaly in NMRI-mice after single X-irradiation with 0.9 Gy or 1.9 Gy on gestation day (gd) 12. The ultrastructural alterations in the ventricular walls are sequentially investigated up to gross developmental damage. The ventricular zone is the most sensitive region in the developing brain. Its constituting undifferentiated and proliferating cells lose their palisade like orientation and fail subsequently to differentiate into primitive neurons, glia cells, or ependymal cells. Structurally this results in the thinning of ventricular walls by more than 50% associated with periventricular oedema and a dilation of the brain ventricles by 20–60%. Damage is clearly more pronounced with the higher dose. Repair processes originate from regions with intact Zonulae adherentes which give also rise to typical globular or cylindrical heterotopic structures; these are known as rosettes and made up from undifferentiated proliferating ventricular cells. Perinatally in these rosettes cell replication persists, at a time when cell production in the ventricular zone has ceased. Histological changes are most prominent in and around the telencephalic roof consisting in replacement of the ependymal lining by a felt of glial fibers, faulty myelinisation, and periventricular oedema; postnatally these structural alterations lead to hydro-micrencephaly. Results from this animal model can be translated to the human situation because the fundamental developmental processes in the brain of mammals are similar despite species related differences of the time scale.This paper is dedicated to Prof. Dr. W. Gössner on the occasion of his 72nd birthday     

Diffraction of X-rays by rippled phosphatidylcholine bilayers

X-ray diffraction patterns have been obtained from the rippled phases of two pure synthetic phosphatidylcholines (dimyristoyl and dipalmitoyl) and mixtures of these phospholipids and cholesterol arranged in oriented multibilayer stacks. These show for the first time in an oriented specimen, a two-dimensionally resolved pattern near the meridian. For example, in pure dipalmitoylphosphatidylcholine the unit cell is two-dimensional and oblique. The ripples have a wavelength of 165.3 Å and are at least 1000 Å wide in the direction perpendicular to this, in the plane of the bilayer. The shape of the ripple is more complex than simply sinusoidal.