Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.      

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Responses to moisture stress in male and female plants of Rumex acetosella L. (Polygonaceae)

Summary Male and female plants of Rumex acetosella were grown on a moisture gradient to measure possible differences in the drought tolerance of the sexes. The growth of both sexes declined under water stress but males were significantly more drought tolerant. This could not be explained by greater water use efficiency in the male plants; measured rates of both photosynthesis and leaf conductance did not differ significantly between the sexes. Multiple discriminant analysis showed that the sexes differed at all moisture regimes in their overall patterns of biomass allocation. Males had proportionately greater investment in root and leaf tissue which could explain their growth advantage over females under water stress. Despite essentially equal water use efficiencies, on a per plant basis males, with more leaf and root biomass, could fix more carbon and more rapidly exploit the local water resource than females. Thus the pattern of biomass allocation rather than intrinsic physiological differences appears to explain the greater drought tolerance of male plants of Rumex acetosella.     

Functional ecology of growth in seedlings versus root sprouts of Fagus grandifolia Ehrh.

We assessed growth differences and the foliar traits underpinning production in paired samples of juvenile American beech (Fagus grandifolia Ehrh.) that originated from seed versus root sprouts. Root sprouts had significantly greater relative extension growth rate and slightly greater leaf mass per unit area compared to seed-derived individuals, but neither light-saturated net photosynthetic rate nor foliar chlorophyll and nitrogen concentrations differed significantly between paired seedlings and sprouts. The greater height growth rate of saplings originating as root sprouts does not result from differing foliar function, but rather depends on translocation of assimilates from the parent tree to sustain this unusual and ecologically important dual regeneration strategy in American beech.     

Niche breadth and range area in North American trees

Identifying factors affecting species distribution is a longstanding goal in ecology and evolution that is accentuated by our need to anticipate climate change impacts. We sought to test whether any phylogenetic effect can be detected in either the environmental characteristics or range attributes of North American trees, and to explore the existence of a general interspecific pattern in the environmental factors influencing species range size. To do so we tested prevailing hypotheses relating climatic and edaphic characteristics to species range size in the North American arboflora (n = 598), using spatial null models to test for the relevance of observed patterns. We found that interspecific variation in the range area of North American trees is strongly related to the environmental regimes characteristic of the species range. Linear models and phylogenetic regressions involving six environmental characteristics explained 83% of the variance in species range area, and affirmed a positive relationship between niche breadth and range size. Tree species that can tolerate a larger variability in local climatic conditions, deal with harsher edaphic conditions, and weak levels of environmental energy tend to have larger range area; this can account for the greater geographic range of species at higher latitudes, the Rapoport effect. There is a significant phylogenetic signal for both range area and limits in North American trees, and for climatic limits, but not for energy or edaphic characteristics associated with species range. These findings highlight the possibility that species with small geographic ranges may be more sensitive to the effects of climate change.     

The role of snail aestivation in transmission of schistosomiasis in changing climatic conditions

Schistosomiasis vector snails are subjected to extreme seasonal changes, particularly in ephemeral rivers and lentic waterbodies. In the tropics, aestivation is one of the adaptive strategies for survival and is used by snails in times of extremely high temperatures and desiccation. Aestivation therefore plays an important role in maintaining the transmission of schistosomiasis. This review assesses the possible impacts of climate change on the temporal and spatial distribution of schistosomiasis-transmitting snails with special emphasis on aestivation, and discusses the effect of schistosome infection on aestivation ability. The impacts of parasite development on snails, as well as physiological changes, are discussed with reference to schistosomiasis transmission. This review shows that schistosome-infected snails have lower survival rates during aestivation, and that those that survive manage to get rid of the infection. In general, snail aestivation ability is poor and survival chances diminish with time. Longer dry periods result in fewer, as well as uninfected, snails. However, the ability of the surviving snails to repopulate the habitats is high.     

Attenuation of pattern recognition receptor signaling is mediated by a MAP kinase kinase kinase

Pattern recognition receptors (PRRs) play a key role in plant and animal innate immunity. PRR binding of their cognate ligand triggers a signaling network and activates an immune response. Activation of PRR signaling must be controlled prior to ligand binding to prevent spurious signaling and immune activation. Flagellin perception in Arabidopsis through FLAGELLIN‐SENSITIVE 2 (FLS2) induces the activation of mitogen‐activated protein kinases (MAPKs) and immunity. However, the precise molecular mechanism that connects activated FLS2 to downstream MAPK cascades remains unknown. Here, we report the identification of a differentially phosphorylated MAP kinase kinase kinase that also interacts with FLS2. Using targeted proteomics and functional analysis, we show that MKKK7 negatively regulates flagellin‐triggered signaling and basal immunity and this requires phosphorylation of MKKK7 on specific serine residues. MKKK7 attenuates MPK6 activity and defense gene expression. Moreover, MKKK7 suppresses the reactive oxygen species burst downstream of FLS2, suggesting that MKKK7‐mediated attenuation of FLS2 signaling occurs through direct modulation of the FLS2 complex.     

1-Thio-beta-D-galactofuranosides: synthesis and evaluation as beta-D- galactofuranosidase inhibitors

Beta-D-galactofuranosidase is a good chemotherapeutic target for the design of inhibitors, since beta-D-galactofuranose is a constituent of important parasite glycoconjugates but is not present in the host mammals. With this aim, we have synthesized for the first time alkyl, benzyl and aryl 1-thio-beta-D-galactofuranosides by condensation of penta-O-benzoyl-alpha,beta-D-galactofuranose with the corresponding thiols, in the presence of SnCl4as catalyst. The complete chemical and spectroscopical characterization of these compounds showed that the reaction was stereoselective. Debenzoylation with sodium methoxide afforded the beta-S-galactofuranosides in high yield. The thioglycosides were tested as inhibitors of the beta-D- galactofuranosidase of Penicillium fellutanum, using for the first time 4-nitrophenyl-beta-D-galactofuranoside as chromogenic substrate. The 4- aminophenyl-1-thio-beta-D-galactofuranoside, obtained by catalytic hydrogenation of the nitrophenyl derivative, was the best inhibitor being then an adequate ligand for the preparation of an affinity phase aimed at the isolation of beta-d-galactofuranosidases from different sources. Also the inhibitory activity of d-galactono-1, 4-lactone was shown.      

BOOK REVIEWS

Book reviewed in this article: Lieth, H. & Schwartz, M.D. (eds.) 1997. Phenology in seasonal climates I . Progress in Biometeorology, Vol. 12. 143 pp. Backhuys Publishers, Leiden. ISBN 90–73348–79-X. Price: USD 42.25.     

Characterization of <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> Beijing isolates from the Mediterranean area

Background  

The Beijing lineage of Mycobacterium tuberculosis is causing concern due to its global distribution and its involvement in severe outbreaks. Studies focused on this lineage are mainly restricted to geographical settings where its prevalence is high, whereas those in other areas are scarce. In this study, we analyze Beijing isolates in the Mediterranean area, where this lineage is not prevalent and is mainly associated with immigrant cases.