Restriction fragment length polymorphism at the HLA-C locus

We have used the HLA-C-specific DNA probe pC250 to investigate restriction fragment length polymorphism (RFLP) at the HLA-C locus. Genomic Southern blot hybridization included DNA prepared from a panel of homozygous typing cells representing serological specificities Cw1 to Cw8 and also from samples representing Cw blanks. Although many restriction nucleases failed to reveal any polymorphism, RFLPs were evident with Taq I, Pvu II, Bst XI, Nde 1, and Nci I in addition to the previously reported Eco RI. In the case of Bst XI, a unique RFLP defined a subset of serologically defined Cw blanks. Comparison of RFLP sizes with restriction fragment lengths obtained from the known HLA-Cw3 gene sequence permitted the localization of intragenic C locus RFLLs and the identification of a variable Taq I site in the second intron, a variable Nci I site near the end of the fourth exon, and a variable Pvu lI site in the fifth intron.     

Characterization of a class of small auxin-inducible soybean polyadenylated RNAs

Four new auxin-responsive RNAs from soybean (Glycine max (L.) Merr., var. Wayne) are described. The RNAs were identified by hybridization to three cDNA probes obtained from a library enriched for sequences which increase in abundance within 60 min after 2,4-D (2,4-dichlorophenoxyacetic acid) treatment. These RNAs appear to define a new class of small (i.e. approximately 550 nucleotides) RNAs that respond extremely rapidly to application of exogenous auxin. In excised elongating hypocotyl sections, an increase in the abundance of these RNAs can be detected 2 to 5 min after treatment with 50 M 2,4-D. This response is half maximal after 10 min and reaches steady state in 60 min. RNA blot analysis shows that these RNAs are expressed differentially in various parts of the seedling. The degree of inducibility by auxin is also organ-specific, with the elongating hypocotyl being the most responsive of the organs tested. The RNAs display identical response specificities with one exception. Accumulation of one RNA, designated 10A, is completely abolished by simultaneous addition of cycloheximide and 2,4-D. This RNA also displays a different 2,4-D dose response than other RNAs examined. These results suggest that more than one mechanism is involved in rapid modulation of gene expression by auxin.     

Leaf water relations and anatomy of a tropical rainforest tree species vary with crown position

Summary Leaf water potentials, osmotic properties and structural characteristics were examined in the Australian tropical rainforest tree species, Castanospermum australe. These features were compared for individuals growing in the understorey and canopy of the undisturbed forest and in an open pasture from which the forest had been cleared. Leaf water potentials during the day declined to significantly lower values in the open-grown and canopy trees than in the understorey trees. During most of the day the opengrown tree experienced the lowest water potentials. These differences were paralleled by significant differences in tissue osmotic properties. The tissue osmotic potential at full hydration was lowest in the open-grown tree (-1.80 MPa), intermediate in the canopy trees (-1.38 MPa), and highest in the understorey trees (-0.80 MPa). As a result, the degree to which high and positive turgor pressures were maintained as water potentials declined was highest in the open-grown tree, intermediate in the canopy trees, and lowest in the understorey trees. The differences in tissue osmotic properties between individuals in the three crown positions were paralleled, in turn, by differences in leaf structual characteristics. Relative to leaves of the canopy and open-grown trees, leaves of the understorey trees had significantly larger epidermal cells with thinner cell walls, larger specific leaf areas and turgid weight: dry weight ratios, and a higher proportion of intercellular air space.Abbreviations ₁ Leaf tissue water potential - _min Lowest value of ₁ during the day ( noon) - _{P=0 1} zero turgor - R Relative water content - P Tissue turgor pressure - Tissue osmotic potential - ₀ at full hydration     

Regulation of blue-green algal buoyancy and bloom formation by light,inorganic nitrogen,C02, and trophic level interactions

In highly eutrophic ponds, buoyancy of the gas-vacuolate blue-green alga Anabaenopsis Elenkinii (Miller) was regulated by complex interactions between chemical and physical parameters, as well as by biological interactions between various trophic levels. Algal buoyancy and surface bloom formation were enhanced markedly by decreased light intensity, and to a lesser extent by decreased CO₂ availability and increased availability of inorganic nitrogen. In the absence of dense populations of large-bodied Cladocera, early season blooms of diatoms and green algae reduced light availability in the ponds thus creating conditions favorable for increased buoyancy and bloom formation by A. Elenkinii. The appearance of blue-green algal blooms could be prevented by a reduced density of planktivorous fish, which allowed development of dense cladoceran populations. The cladocerans limited the growth of precursory blooms of diatoms and green algae, and given the resulting clear-water conditions, buoyancy of A. Elenkinii was reduced, and blue-green algal blooms never appeared.     

Autoantibodies specific for the cardiac myosin isoform are found in mice susceptible to Coxsackievirus B3-induced myocarditis

Several mouse strains are susceptible to immunopathic myocarditis after infection with Coxsackievirus B3 (CB3). This disease is associated with autoantibodies that are directed against myosin. In this study we characterized sera from CB3-infected mice for their reactivity with three different myosin isoforms (heart, skeletal muscle, and brain myosins) and for autoantibody isotype by using an ELISA. Competitive inhibition assays and absorption studies with various myosins demonstrated the presence of two autoantibody populations in sera of susceptible A.CA and A.SW mice. The first was specific for cardiac myosin and was mainly IgG. The second antibody population cross-reacted with heart, skeletal muscle, and brain myosin and was mainly IgM. B10.PL/SgSf and B10.A/SgSf mice, which do not develop immunopathic myocarditis, produced only the IgM autoantibody population cross-reactive with all three myosin isoforms. Because the heart-specific myosin autoantibodies were found exclusively in the mouse strains that developed immunopathic myocarditis, they can be considered a serologic marker for autoimmune heart disease.     

Characterization of the T3+T4+T8+ thymocyte intermediate in vitro

Sensitive two-color fluorescence staining and cell-sorting techniques were used to isolate a T4+T8+ thymocyte subpopulation with high T3 density from human thymocyte cultures. Previously, this population was shown to give rise to both T4+T8- and T8+T4- thymocytes. In the present study, this T3+T4+T8 population was shown to be functionally as well as phenotypically distinct from either T8+T4- cells or T4+T8- cells present in the same culture. The T3+T4+T8+ cell had intermediate cytotoxic capacities relative to T8+T4- and T4+T8- thymocyte fractions. The proliferative capacity of the T4+T8+ population although less than that of the T8+T4- subset exceeded the proliferative response of the T4+T8- population. The time of appearance of large numbers of T3+T4+T8+ cells in culture as well as functional properties exhibited by T3+T4+T8+ cells are consistent with the notion that the T3+T4+T8+ cell represents an activated intermediate in thymocyte differentiation. The T3+T4+T8+ thymocyte may be an important intermediate in in vivo as well as in in vitro thymic differentiation. Moreover, the analysis of its functional properties may contribute to an understanding of functional responses exhibited by the most mature (T3+) population isolated from human thymus.