Colonies ofReticulitermes flavipes andR. santonensis were collected from the southeastern United States (Georgia) and the southwest of France (Charente-maritime). Defensive compounds and cuticular hydrocarbons were identified by gas chromatography-mass spectrometry and quantified by gas chromatography using an internal standard for each caste and all colonies. These analyses show that although the cuticular hydrocarbons ofR. santonensis in Europe andR. flavipes in Georgia are identical, their relative proportions are different. However, the defensive compounds synthesized by their soldiers are different. A strong chemical polymorphism between sympatric colonies ofR. flavipes in the SW United States was detected in terms of both the hydrocarbons of the workers and soldiers and in the defensive secretions of the soldiers. The six defensive secretion phenotypes are based on the presence or absence of terpenes whereas the cuticular hydrocarbon phenotypes are based on significant differences in the proportions of the various components. A multivariate analysis (analysis of principal components) clearly permitted discrimination of four phenotypes (three inR. flavipes and one inR. santonensis) without intermediates. The hydrocarbons responsible for these variations were identified, and it was shown that the variations are neither seasonal nor geographic. The phenotypes of the cuticular hydrocarbons (workers and soldiers) and defensive compounds are linked in each colony, forming in three groups inR. flavipes Georgia, one subdivided into four subgroups according to the defensive secretion phenotypes. The role of these polymorphisms is discussed and ethological tests indicate that the chemical polymorphism do not determine aggressive behavior. The taxonomic significance of these results is considered and two hypothesis are formulated: (1) We only detected a strong genetic polymorphism in one unique species, and we believe thatR. santonensis was introduced into Europe in the last century from oneR. flavipes colony. (2) Chemical variability characterizes the sibling species that can be grouped into the same subspeciesR. flavipes. Unknown mechanisms of reproductive isolation separate them.
N-arginine (R) dibasic (NRD) convertase (nardilysin; EC 3.4.24.61), a metalloendopeptidase of the M16 family, specifically cleaves peptide substrates at the N-terminus of arginines in dibasic motifs in vitro. In rat testis, the enzyme localizes within the cytoplasm of spermatids and associates with microtubules of the manchette and axoneme. NRD1 and NRD2 convertases, two NRD convertase isoforms, differ by the absence (isoform 1) or presence (isoform 2) of a 68-amino acid insertion close to the active site. In this study, we overexpressed both isoforms, either by vaccinia virus infection of BSC40 cells or transfection of COS-7 cells. The partially purified enzymes exhibit very similar biochemical and enzymic properties. Microsequencing revealed that NRD convertase is N-terminally processed. Results of immunocytofluorescence, immunoelectron microscopy and subcellular fractionation studies argue in favour of a primary cytosolic localization of both peptidases. Although the putative signal peptide did not direct NRD convertase into microsomes in an in vitro translation assay, biotinylation experiments clearly showed the presence of both isoforms at the cell surface. In conclusion, although most known processing events at pairs of basic residues are achieved by proprotein convertases within the secretory pathway, NRD convertase may fulfil a similar function in the cytoplasm and/or at the cell surface.
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