The preservation of the ability of cultured quail wing bud mesoderm to elicit a position-related differentiative response

A previous study showed that grafting wedges of fresh anterior quail wing mesoderm into posterior slits of chick wing buds resulted in the formation of rods and nodules of cartilage in a high percentage of cases (B. Carlson, 1983, Dev. Biol. 101, 97-105). The purpose of the present study was to determine if a similar response could be elicited by grafting pieces of mesoderm that had been cultured in vitro. When pieces of 1-day cultured anterior mesoderm from stage 17-24 donors were grafted into standard posterior slits of chick wing buds, the percentages of supernumerary structures differed little from those which formed after the grafting of pieces of fresh mesoderm. In a time series, grafts of stage 22-23 anterior mesoderm which had been cultured for 1-4 days retained the ability to form cartilage after being grafted into posterior locations. A time series showed that the duration of this retention was longer in cultured mesoderm than it was in mesoderm that remains in the donor wing bud.     

Anaphase chromosome movement in the unequally dividing grasshopper neuroblast and its relation to anaphases of other cells

The positions of the two sets of chromosome kinetochores, the spindle poles, cell membrane adjacent to the poles, and cleavage furrow of grasshopper neuroblasts in culture at 38°C were determined at short-time intervals during anaphase. The percent of motion due to poleward movement and spindle elongation, which coincide in time, were calculated for each minute, the former falling from 61% in the first minute to 15% in the seventh minute, and increasing to 86% in the final minute, probably as a result of pressure and bending of the spindle. Of the total chromosome movement during anaphase 44.6% is due to poleward movement of the daughter kinetochores and 55.4% to spindle elongation. The maximum velocity of a set of kinetochores is 3.41 m/min and the mean velocity 1.86 m/min (one-half the rate of separation). Various studies of anaphase chromosome movement in different cells and different species suggest certain generalizations, some of which are based on very small samples and so must be considered quite tentative: (1) The combination of poleward movement and spindle elongation is much more frequent than either acting alone. (2) These components of movement may coincide in time, overlap, or spindle elongation may follow poleward movement, but spindle elongation never begins before poleward chromosome movement. (3) There is an optimum temperature for the rate of chromosome movement, above and below which the rate gradually decreases. (4) In homoiothermic animals this optimum occurs at normal body temperature. (5) In homoiothermic animals the velocity falls more rapidly with a decrease in temperature than in poikilothermic animals. (6) Animals with large chromosomes (amphibia, grasshoppers) have higher chromosome velocities than those with small chromosomes. (7) Non-meiotic cells and secondary spermatocytes have higher velocities than primary spermatocytes of the same species. (8) Chromosome velocity is lower in malignant than non-malignant cells. (9) Chromosome velocity tends to be positively correlated with the distance the chromosomes travel during anaphase.     

Plants interact with microbial polysaccharides

Plants are resistant to almost all of the microorganisms with which they come in contact. In response to invasion by a fungus, bacterium, or a virus, many plants produce low molecular weight compounds, phytoalexins, which inhibit the growth of microorganisms. Phytoalexins are produced whether or not the invading microorganism is a pathogen. The production of phytoalexins appears to be a widespread mechanism by which plants attempt to defend themselves against pests. Molecules of microbial origin which trigger phytoalexin accumulation in plants are called elicitors. Structural polysaccharides from the mycelial walls of several fungi elicit phytoalexin accumlation in plants. Approximately 10 ng of the polysaccharide elicits the accumulation in plants of more than sufficient amounts of phytoalexin to stop the growth of microorganisms in vitro. The best characterized elicitors have been demonstrated to be β-1,3-glucans with branches to the 6 position of some of the glucosyl residues. Oligosaccharides, produced by partial acid hydrolysis of the mycelial wall glucans, are exceptionally active elicitors. The smallest oligosaccharide which is still an effective elicitor is composed of about 8 sugar residues. Bacteria also elicit phytoalexin accumulation in plants, but the Rhizobium symbionts of legumes presumably have a mechanism which allows them to avoid either eliciting phytoalexin accumulation or the effects of the phytoalexins if they are accumulated. The lectins of legumes bind to the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It is not known whether the lectin-lipopolysaccharide interaction is involved with the establishment of symbiosis. However, evidence will be presented that suggests that lectins are, in fact, enzymes capable of modifying the structurs of the lipopolysaccharides of their symbiont, but not of their non-symbiont, Rhizobium. It will also be shown that the lipopolysaccharides isolated from different Rhizobium species and from different strains of individual Rhizobium species have different sugar compositions. Thus, the different strains of a single Rhizobium species are as different from one another as the different species of Salmonella and other gram-negative bacteria. This conclusion is substantiated by experiments demonstrating that antibodies to the lipopolysaccharide from a single Rhizobium strain can differentiate that strain from other strains of the same species as well as from other Rhizobium species. The role in symbiosis of the strain-specific O-antigens is unknown.     

Resistance to moloney murine sarcoma virus-induced tumorigenesis in NK-deficient beige mice

C57BL/6J-bg^J$\text{bg}\text{bg}$ mice are reported to be less susceptible to tumor induction by threshold doses of Moloney murine sarcoma virus than their +/bg littermates, and there are no significant differences between $\text{bg}\text{bg}$ and +/bg mice in which tumors were induced with respect to tumor latency, size, and regression rate. The difference in tumor frequency cannot be accounted for by M-MSV boosting of activity in $\text{bg}\text{bg}$ mice or by depression of activity in +/bg animals.     

Induction of adult-type nicotinic acetylcholine receptor gene expression in noninnervated regenerating muscle

Expression of adult-type nicotinic acetylcholine receptors at the neuromuscular junction is thought to result from selective induction of their genes in endplate-associated nuclei due to local neurotrophic control. However, denervation studies indicate that endplate-specific expression can be maintained in the absence of the nerve. We investigated the role played by the basal lamina in this expression by assaying for the adult-type-specific epsilon RNA in noninnervated regenerating muscle. We found that this RNA is locally expressed beneath the old endplates after 10 days of regeneration. At earlier times epsilon RNA is also found in areas other than the endplate region. These results indicate that in adult muscle the basal lamina contains all the components necessary to direct nicotinic acetylcholine receptor gene expression to the endplate.     

Occlusal force and craniofacial biomechanics during growth in rhesus monkeys

The masticatory muscles in 132 anesthetized male and female rhesus monkeys ranging in age from juvenile to adult were unilaterally stimulated. Muscle forces and speeds were measured with a bite force transducer positioned at the incisors, premolars, and molars during twitch and tetanic contractions. Lateral cephalographs of all animals were used to estimate the orientation and mechanical advantage of the masticatory muscles. Results showed that maximal occlusal forces increased at a greater rate than body weight during growth. However, maximal occlusal forces increased isometrically relative to mandibular length. Mean forces at the incisors ranged from 70.3 newtons (n) in juveniles up to 139.9 n in adult males. Forces at the molars were 2-2.5 times greater than at the incisors. Time-to-peak tension decreased with increasing body size from 44.1 msec in juveniles to 37.4 msec in adult females to 31.0 msec in adult males. Regression analysis showed that adult males have faster muscles than adult females or juveniles even when corrected for body size. Temporalis and masseter orientation was found to change little throughout growth. The mechanical advantage of the masseter and temporalis muscles for producing occlusal forces on the distal molars improved between juveniles and adults, which is contrary to findings of Oyen et al. (Growth 43:174-187, 1979). Among adults, females had a greater mechanical advantage of the masseter muscles than males.