Functional role of phenylacetic acid from metapleural gland secretions in controlling fungal pathogens in evolutionarily derived leaf-cutting ants

Fungus-farming ant colonies vary four to five orders of magnitude in size. They employ compounds from actinomycete bacteria and exocrine glands as antimicrobial agents. Atta colonies have millions of ants and are particularly relevant for understanding hygienic strategies as they have abandoned their ancestors'' prime dependence on antibiotic-based biological control in favour of using metapleural gland (MG) chemical secretions. Atta MGs are unique in synthesizing large quantities of phenylacetic acid (PAA), a known but little investigated antimicrobial agent. We show that particularly the smallest workers greatly reduce germination rates of Escovopsis and Metarhizium spores after actively applying PAA to experimental infection targets in garden fragments and transferring the spores to the ants'' infrabuccal cavities. In vitro assays further indicated that Escovopsis strains isolated from evolutionarily derived leaf-cutting ants are less sensitive to PAA than strains from phylogenetically more basal fungus-farming ants, consistent with the dynamics of an evolutionary arms race between virulence and control for Escovopsis, but not Metarhizium. Atta ants form larger colonies with more extreme caste differentiation relative to other attines, in societies characterized by an almost complete absence of reproductive conflicts. We hypothesize that these changes are associated with unique evolutionary innovations in chemical pest management that appear robust against selection pressure for resistance by specialized mycopathogens.     

Epididymal maturation and the acrosome reaction in mouse sperm: response to zona pellucida develops coincident with modification of M42 antigen

Development of the sperm's capacity to interact with the zona pellucida was investigated at the stage when the acrosome reaction (AR) is induced. The response of epididymal sperm to agents that affect the occurrence of the AR was used to monitor maturational changes. Despite the finding that sperm from the three main epididymal regions were competent to undergo ARs induced by the divalent cation ionophore A23187 (56% AR, 74% AR, and 83% AR in caput, corpus, and cauda, respectively), the cells' responses to solubilized zonae pellucidae were different. When challenged with 5 zonae equivalents/microliter, both corpus and cauda sperm shed their acrosomes in high numbers (75% AR and 86% AR, respectively), whereas caput sperm did not (23% AR). Previous work has shown that the presence of M42 monoclonal antibody (mAb) during in vitro and in vivo fertilization inhibits sperm penetration through the zona pellucida by specific interference with zonae pellucidae-induced ARs. In this study, presence of the M42 mAb did not affect the incidence of A23187-induced ARs, whereas the zona-induced ARs that occurred in both corpus and cauda sperm were inhibited fully with M42 immunoglobulin (Ig) G. In addition, the antigen recognized by M42 mAb on sperm, termed M42 Ag, was examined during epididymal maturation. Although antigen localization appeared indistinguishable by immunofluorescence on sperm taken from the caput, corpus, and cauda regions of the epididymis, modification of this antigen during epididymal transit was detected. Equilibrium-binding studies using 125I-M42 IgG demonstrated a progressive increase during epididymal transit in the amount of M42 mAb that bound to fixed cells. Corpus and cauda sperm bound 185% and 240%, respectively, of the 125I-M42 IgG detected on caput sperm. These changes in expression of M42 Ag paralleled a structural change: the Mr of the antigen decreased from a 195,000/210,000 doublet in caput sperm to a 185,000/200,000 doublet in corpus and cauda sperm, as determined by immunoblot analysis of sodium dodecyl sulfate (SDS)-extracted sperm. Results presented here demonstrate that mouse sperm develop the capacity to undergo a zona-induced AR during epididymal maturation. The M42 antigen, which is involved in the zona-induced AR, is modified during epididymal transit coincident with development of the sperm's responsiveness to zonae. Our working hypothesis, based on these results, is that development of the sperm's capacity to undergo a physiological AR is related to modification of M42 Ag.     

Phospholipase D activity in nontransformed and transformed fibroblasts.

Rat embryo fibroblasts (REF52 cells) and the simian virus 40 transformed derivative (WT6 Ag6) were employed to characterize phospholipase D (PLD) activity in normal and transformed cells. In cells prelabeled with [3H]myristic acid or [3H]glycerol and treated with 12-O-tetradecanoylphorbol-13-acetate (TPA, 50 ng/ml medium) or vasopressin (VP, 100 ng/ml medium) in the presence of ethanol, the formation of labeled phosphatidylethanol (PEt) was 3- to 5-fold higher in REF52 cells than in the transformed cells. The transphosphatidylation of phosphatidylcholine (PC) to PEt was further examined in cell-free assay systems. Results demonstrated that the formation of PEt in the cell-free assays was dependent on the mode of substrate presentation and the source of the PC. With endogenous membrane-bound substrate, the formation of [3H]myristoyl-PEt was 5-fold higher in homogenates derived from normal cells as compared to transformed cell homogenates. In experiments using exogenous labeled PC isolated from either REF52 or transformed cells as substrate, cell-free PLD activity differed greatly with regard to the source of the PC. The formation of PEt from REF52-derived PC was approx. 4-fold higher as compared to PEt formed with PC derived from the transformed cells, irrespective of enzyme source. The results demonstrate that PLD in intact nontransformed fibroblasts is activatable by TPA and VP to a greater extent than in the transformed counterpart. The results from cell-free assays suggest that PLD activity is more dependent on the type of PC substrate than on the source of the enzyme.     

Population Genetics of Tandem Repeats in Centromeric Heterochromatin: Unequal Crossing over and Chromosomal Divergence at the Responder Locus of Drosophila Melanogaster

The Responder (Rsp) locus in Drosophila melanogaster is the target locus of segregation distortion and is known to be comprised of a tandem array of 120-bp repetitive sequences. In this study, we first determined the large scale molecular structure of the Rsp locus, which extends over a region of 600 kb on the standard sensitive (cn bw) chromosome. Within the region, small Rsp repeat arrays are interspersed with non-Rsp sequences and account for 10-20% of the total sequences. We isolated and sequenced 32 Rsp clones from three different chromosomes. The main results are: (1) Rsp repeats isolated from the same chromosome are not more similar than those from different chromosomes. This implies either that there are more homologous exchanges at the Rsp locus than expected or, alternatively, that the second chromosomes of D. melanogaster have diverged from one another more recently at the centromeric heterochromatin than at the nearby euchromatin. (2) The repeats usually have a dimeric structure with an average difference of 16% between the left and right halves. The differences allow us to easily identify the products of unequal exchanges. Despite the large differences between the two halves, exchanges have occurred frequently and the majority of them fall within a 29-bp interval of identity between the two halves. Our data thus support the suggestion that recombination depends on short stretches of complete identity rather than long stretches of general homology. (3) Frequent unequal crossover events obscure the phylogenetic relationships between repeats; therefore, different parts of any single repeat could often have different phylogenetic histories. The high rate of unequal crossing over may also help explain the evolutionary dynamics of the Rsp locus.     

Gross (mesoscopic) and applied anatomy of the anterior inferior cerebellar artery in man with special reference to its course through the cerebellopontine angle region.

In the present paper, we describe anatomical variants of the anterior inferior cerebellar artery in man for applicative purposes. Our goal was to provide the surgeon with a detailed anatomical view of the region. This is similar to what he may observe through the surgical microscope using modern microsurgical techniques. We have focused our attention on the segments of the artery comprising its origin, its course until it reaches the cerebellum and its main collateral branches. Our results confirm the great variability of the elements under study, but enable the establishment of a few basic variational patterns. These patterns together with their relative frequency may be helpful in microsurgery.     

Vertebrate class distribution of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine acetylhydrolase in serum

Serum from numerous mammals and lower vertebrates contains an enzyme activity that is specific for the hydrolysis of the acetate moiety of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF, platelet activating factor). Acetylhydrolase (EC 3.1.1.47, 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine acetylhydrolase) was found in all mammalian sera with activity ranging from 11 (fetal calf) to 178 (rabbit) pmol acetate liberated/microliter serum/min. The enzyme is not present in avian serum but is a constituent of reptiles and bony fishes.     

Nature of the rabbit acrosome reaction-inducing activity of follicular fluid.

Follicular fluid samples from rabbits, cats, pigs, women and cows had acrosome reaction-inducing activity (ARIA) on rabbit spermatozoa as determined by differential staining after incubation with these fluids. Activity was retained after dialysis and at least 50% was found to be labile when heated to 56 degrees C for as little as 20 min. The induction of the acrosome reaction by bovine follicular fluid showed a dependence on the concentration of follicular fluid and spermatozoa and on calcium ions, and had a pH optimum of approximately 8. Enzyme treatments showed that proteases destroyed the ARIA and this activity was completely blocked by treatment of bovine follicular fluid with goat anti-bovine antiserum. Electron microscope observations indicated the similarity of the reactions observed to that occurring in vivo. It is concluded that the rabbit acrosome reaction inducing-activity of bovine follicular fluid is a serum component(s), probably a protein(s) of high molecular weight.     

Ferralterin: An iron-sulfur protein functional in enzyme regulation in photosynthesis

The chloroplast new protein factor that was recently shown to link light to the activation of fructose 1,6-bisphosphatase was identified as a previously unrecognized iron-sulfur protein. This protein, given the name “ferralterin,” was purified to homogeneity from spinach leaves and from the blue-green alga (cyanobacterium) Nostoc muscorum. Ferralterin from both sources showed a visible absorption peak at 410nm, a molecular weight of about 30,000 and (provisionally) 4 g-atoms per mole each of nonheme iron and acid labile sulfide. The homogeneous ferralterin preparations catalyzed a light-dependent activation of chloroplast fructose 1,6-bisphosphatase that was dependent only on chlorophyll-containing membranes.