Correlation of cell surface antigen expression on human thymocytes by multi-color flow cytometric analysis: implications for differentiation

Thymocytes undergo a complex series of phenotypic and genotypic changes during maturation in the thymus. This dynamic process involves qualitative and quantitative changes in the expression of certain cell surface differentiation antigens. In this study, we have directly examined the relationship of T cell differentiation antigen expression on normal human thymocytes by using multi-color immunofluorescence and multi-parameter flow cytometric analysis. The results from these studies have provided new insights into the complexity of antigen expression during thymic maturation and suggest that the CD3/T cell antigen receptor complex is expressed early in the development of thymocytes. Direct quantitative measurements of antigen expression by using multi-parameter flow cytometric analysis also suggest quantitative co-regulation of certain antigens (e.g., CD3 and CD5) during thymic maturation.     

Dictyosome vesicle production and plasma membrane turnover in auxin-stimulated outer epidermal cells of coleoptile segments fromAvena sativa (L.)

Summary Dark grown coleoptile segments were floated on solutions of IAA alone and of IAA and the secretion inhibitors cytochalasin and monensin. The secretion inhibitors prevented normal elongation of the tissue segments, the monensin inhibition being virtually complete while cytochalasin gave a 40% reduction over the first six hours with little further further elongation in the following 18 hours. Vesicle production was assessed in outer epidermal cells after 6 hours of IAA-stimulated elongation using the vesicle accumulation method following a cytochalasin-block of vesicle transport. The results were compared with the area of plasma membrane required to enable cell elongation to proceed at the observed rate. The area of vesicle membrane delivered to the cell surface exceeded this requirement to such an extent that at least 65% of the delivered membrane must be recycled back into the cytoplasm. Expressed in terms of the whole cell, the plasma membrane turnover rate was found to be once every 200 minutes. It is concluded that limitation of elongation by secretion inhibitors is more likely to reflect a requirement for the vesicle contents than the vesicle membrane. These results are compared with those obtained from other secretory systems using a similar approach.Abbreviations IAA indole acetic acid - DMSO dimethyl sulphoxide - D dictyosome - ER endoplasmic reticulum - V vesicle     

Evaluating Hypotheses on the Evolution of Helping Behaviour in the Bell Miner (Manorina melanophrys)

In an analysis of the pattern of helping at the nest in bell miners (Manorina melanophrys), Clarke (1989) examined five hypotheses that could explain the evolution of helping behaviour in this species. We applaud the attempt by Clarke to consider many different hypotheses, but believe that more careful formulation of the hypotheses, more appropriate statistical analyses, and eventual experimental testing are required before his conclusions can be accepted.     

Host plant growth characteristics as determinants of abundance and phenology in jumping plant-lice on downy willow

1. Salix lapponum host plants at an upper altitudinal site differed significantly in size, structural density, phenology, growth performance, and spatial isolation from those growing at a lower site. 2. Plant differences were paralleled by significant differences in psyllid population density and phenology parameters, with psyllid population density, percentage of catkins occupied, and phenological development relatively lower or retarded at the upper site. Population densities at the upper site, nevertheless, remained high. 3. Plant measurements were good predictors of insect density, often explaining up to 73% of the variance in abundance among plants at a given site. 4. Sets of four plant characters identified by best subsets regression were better predictors of psyllid density and development than single factors, although differences were often not great and the combinations of characters selected by multiple regression sometimes differed from the best single predictors. 5. Best single predictors of psyllid density on catkins were measurements of plant size, particularly height, length, and basal stem diameter. Shoot density and catkin phenology were occasionally important but plant isolation and prior growth performance were less important. 6. By contrast with density, age structure of the psyllid population was predicted best from plant phenological measurements, notably catkin phenology.