The evolutionary transformation of phyllopodous to stenopodous limbs in the Branchiopoda (Crustacea)--is there a common mechanism for early limb development in arthropods?

Arthropods and in particular crustaceans show a great diversity concerning their limb morphology. This makes the homologization of limbs and their parts and our understanding of evolutionary transformations of these limb types problematical. To address these problems we undertook a comparative study of the limb development of two representatives of branchiopod crustaceans, one with phyllopodous the other with stenopodous trunk limbs. The trunk limb ontogeny of a 'larger branchiopod', Cyclestheria hislopi ('Conchostraca') and the raptorial cladoceran Leptodora kindtii (Haplopoda) has been examined by various methods such as SEM, Hoechst fluorescent stain and expression of the Distal-less gene. The early ontogeny of the trunk limbs in C. hislopi and L. kindtii is similar. In both species the limbs are formed as ventrally placed, elongate, subdivided limb buds. However, in C. hislopi, the portions of the early limb bud end up constituting the endites and the endopod of the phyllopodous filtratory limb in the adult, whereas in L. kindtii, similar limb bud portions end up constituting the actual segments in the segmented, stenopodous, and raptorial trunk limbs of the adults. Hence, the portions of the limbs corresponding to the endites of the phyllopodous trunk limbs in C. hislopi (and other 'larger branchiopods') are homologous to the segments of the stenopodous trunk limbs in L. kindtii. It is most parsimonious to assume that the segmented trunk limbs in L. kindtii have developed from phyllopodous limbs with endites and not vice versa. This study has demonstrated at least one way in which segmented limbs have been derived from phyllopodous, multi-lobate limbs during evolution. Similar pathways can be assumed for the evolution of stenopodous, segmented and uniramous limbs in other crustaceans. Irrespective of the differences in the adult limb morphology, the early patterning of arthropod limbs seems to follow a similar principle.     

Algesia and local responses induced by neurokinin A and substance P in human skin and temporal muscle

Neurokinin A (NKA), substance P (SP) and the two peptides combined (SP + NKA) were injected intracutaneously on the forearm and into the temporal muscle of healthy volunteers. Pain intensity, cutaneous wheal and flare responses and tenderness of the temporal muscle were quantitated. SP but not NKA induced cutaneous pain. This relates the algesic effect of SP to the specific N-terminal amino acid sequence of the peptide, not shared by NKA. NKA, however, potentiated the algesic effect of SP as SP + NKA induced a significantly prolonged cutaneous pain sensation. Both peptides induced wheals, but only SP induced flare. These results confirm previous studies relating wheal formation to the identical C-terminal amino acid sequence of the two peptides and flare reaction to the N-terminal part of SP. Injections into the temporal muscle did not cause pain or tenderness.     

Comparison of transfer RNA and ribosomal RNA intron splicing in the extreme thermophile and archaebacterium Desulfurococcus mobilis

The structure of the exon-intron boundary was compared for an intron within 23S ribosomal RNA of Desulfurococcus mobilis and a newly discovered intron in tRNA(Met) from the same organism. The occurrence of a putative common structural feature suggests that intron excision occurs by the same mechanism. The possible recognition of this structural feature by the cleavage enzyme was investigated for the ribosomal RNA intron using RNA substrates exhibiting various exon and intron deletions. The results support the involvement of the structural features in the cleavage process. The evolutionary implications of these results are considered.     

Distamycin inhibition of topoisomerase I-DNA interaction: a mechanistic analysis.

Inhibition of eukaryotic DNA topoisomerase I by the minor groove binding ligand, distamycin A, was investigated. Low concentrations of the ligand selectively prevented catalytic action at a high affinity topoisomerase I binding sequence. A restriction enzyme protection assay indicated that the catalytic cycle was blocked at the binding step. Distamycin binding sites on DNA were localized by hydroxyl radical footprinting. A strongly preferred site mapped to a homopolymeric (dA).(dT)-tract partially included in the essential topoisomerase I binding region. Mutational elimination of the stable helix curvature associated with this ligand binding site demonstrated that (i) the intrinsic bend was unessential for efficient binding of topoisomerase I, and (ii) distamycin inhibition did not occur by deformation of a stable band. Alternative modes of inhibition are discussed.     

Suppressible P-element alleles of the vestigial locus in Drosophila melanogaster

Summary A series of P-element insertion mutations at one site in the vestigial (vg) locus was tested for cytotype dependent effects on vg expression. The mutant phenotypes for four P-element vg alleles were suppressed when the alleles were stabilized in the P-cytotype. The suppression was observed whenever repressor-producing P-elements were present in the genome. Genetic and molecular analysis indicated that the suppression is not due to excision or other irreversible alterations of the inserts. The results are consistent with a model in which somatic P-element repressor binding to the ends of P-element inserts can modify the effects of these inserts on target gene expression.     

Calcitonin gene-related peptide, neurokinin A and substance P: effects on nociception and neurogenic inflammation in human skin and temporal muscle.

Calcitonin gene-related peptide (CGRP) was injected alone and in combination with substance P (SP) or neurokinin A (NKA) into the forearm skin and temporal muscle of human volunteers. In the skin, 50 pmol of CGRP induced a wheal response and a delayed erythema. No pain was recorded. No interaction between CGRP and SP or NKA was observed. In the temporal muscle, 200 pmol of CGRP alone did not induce pain or tenderness but, in combination with SP or NKA, CGRP elicited a significant pain sensation. It is concluded that CGRP may be involved in neurogenic inflammation and that only SP, of the three peptides present in nociceptive C fibers, seems to be of major importance in relation to cutaneous nociception. Simultaneous neurogenic release of CGRP and other neuropeptides in skeletal muscle may induce myofascial pain.     

Predation and potential transfer of pollen in a population of Saxifraga hirculus

Body surface pollen load and gut pollen (pollen diet load) of flower visitors in a Danish population of Saxifraga hirculus were analyzed. The four most frequent visitors, Eurimyia lineata (Syrphidae), Neoascia tenur (Syrphidae), Asindulum nigrum (Mycetophilidae), and Zygaena trifolii (Zygaenidae) had total surface loads (and S. hirculus loads) of 1031 (771), 137 (106), 108 (78), and 318 (27) pollen grains, respectively. Other syrphid visitors had on average a load of 407 (192) pollen grains. Males of E. lineata, N. tenur , and A. nigrum carried more surface pollen than the females; females of E. lineata had a lot of pollen from Ranunculus acris and S. hirculus and males had a lot from S. hirculus . Females of N. tenur carried pollen mostly from S. hirculus, Lotus uliginosus and Galium uliginosum ; males carried pollen mostly from S. hirculus . The surface pollen load of A. nigrum was dominated by S. hirculus pollen, whereas that of Z. trifolii was dominated by Cirsium palustre and Lychnis flos-cuculi pollen. The amount and kind of pollen varied enormously both intraspecifically and interspecifically. Eurimyia lineata, N. tenur and other syrphids had total pollen diet loads (and S. hirculus pollen diet loads) of approximately 14900 (657), 3739 (2327) and 17784 (13040). The average syrphid contained pollen from five plant species, only one to two, however, were quantitatively important. The average diet load in females was nine times that in males in both E. lineata and N. tenur. Eurimyia lineata ate a lot of R. acris; N. tenur ate a lot of S. hirculus and G. uliginosum . Generally, no correlation was observed between size or season and the composition of surface load and diet load. Eurimyia lineata made most of the pollen visits. Thus, the seed set from this Danish population of S. hirculus was dependent on a single syrphid species.     

Pretreatment of wheat straw using combined wet oxidation and alkaline hydrolysis resulting in convertible cellulose and hemicellulose

The wet oxidation process of wheat straw has been studied as a pretreatment method to attain our main goal: To break down cellulose to glucose enzymatic, and secondly, to dissolve hemicellulose (e.g., for fermentation) without producing microbial inhibitors. Wet oxidation combined with base addition readily oxidizes lignin from wheat straw facilitating the polysaccharides for enzymatic hydrolysis. By using a specially constructed autoclave system, the wet oxidation process was optimized with respect to both reaction time and temperature. The best conditions (20 g/L straw, 170 degrees C, 5 to 10 min) gave about 85% w/w yield of converting cellulose to glucose. The process water, containing dissolved hemicellulose and carboxylic acids, has proven to be a direct nutrient source for the fungus Aspergillus niger producing exo-beta-xylosidase. Furfural and hydroxymethyl-furfural, known inhibitors of microbial growth when other pretreatment systems have been applied, were not observed following the wet oxidation treatment. (c) 1996 John Wiley & Sons, Inc.