Flaxseed (Linum usitatissimum L.) extract as well as (+)-secoisolariciresinol diglucoside and its mammalian derivatives are potent inhibitors of α-amylase activity

Type 2 diabetes mellitus (T2DM) is one of the common global diseases. Flaxseed is by far the richest source of the dietary lignans (i.e., secoisolariciresinol diglucoside) which have been shown to delay the development of T2DM in animal models. Herein, we propose the first evidences for a mechanism of action involving the inhibition of the pancreatic α-amylase (EC 3.2.1.1) by flaxseed-derived lignans that could therefore constitute a promising nutraceutical for the prevention and the treatment of T2DM.     

A micromethod for serotyping Bacillus thuringiensis

P. LAURENT, H. RIPOUTEAU, V. COSMAO DUMANOIR, E. FRACHON AND M.-M. LECADET. 1996. Serotyping of Bacillus thuringiensis is possible using 96-well microplates instead of tubes. The advantages are a reduction on the incubation time from 120 to 75 min and the amounts of antisera and bacterial suspensions needed 10-fold.     

Nectar robbing improves male reproductive success of the endangered Aconitum napellus ssp. lusitanicum

Nectar robbery is usually thought to impact negatively on the reproductive success of plants, but also neutral or even positive effects have been reported. Very few studies have investigated the effects of nectar robbing on the behaviour of legitimate pollinators so far. Such behavioural changes may lead to the reduction of geitonogamy or to increased pollen movement. We simulated nectar robbing in experimental sites as well as in natural populations of Aconitum napellus ssp. lusitanicum, a rare plant pollinated by long-tongued bumblebees. In an experimental setup, we removed the nectaries of 40 % of the flowers, which is similar to rates of robbing observed in wild populations. Patches of plants with experimentally robbed flowers were compared with control patches containing plants with untreated flowers. We observed pollinator behaviour, mimicked male reproductive success (pollen dispersal) using fluorescent dye, and measured female reproductive success (seed set). The main legitimate visitors were bumblebees while honeybees were often observed robbing nectar. They did so by “base working”, i.e. sliding between tepals. Bumblebees tended to visit fewer flowers per plant and spent less time per single flower when these had been experimentally robbed. This change in behaviour consequently increased the proportion of flowers visited by bumblebees in patches with robbed flowers. Fluorescent dye mimicking pollen flow was dispersed larger distances after pollinators had visited patches with robbed flowers compared to control patches. Average seed set per plant was not affected by nectar robbing. Our results demonstrated that A. napellus does not suffer from nectar robbery but may rather benefit via improved pollen dispersal and thus, male reproductive success. Knowledge on such combined effects of behavioural changes of pollinators due to nectar robbery is important to understand the evolutionary significance of exploiters of such mutualistic relationships between plants and their pollinators.     

Independent specialisation of myosin II paralogues in muscle vs. non-muscle functions during early animal evolution: a ctenophore perspective

ABSTRACT: BACKGROUND: Myosin II (or Myosin Heavy Chain II, MHCII) is a family of molecular motors involved in the contractile activity of animal muscle cells but also in various other cellular processes in non-muscle cells. Previous phylogenetic analyses of bilaterian MHCII genes identified two main clades associated respectively with smooth/non-muscle cells (MHCIIa) and striated muscle cells (MHCIIb). Muscle cells are generally thought to have originated only once in ancient animal history, and decisive insights about their early evolution are expected to come from expression studies of Myosin II genes in the two non-bilaterian phyla that possess muscles, the Cnidaria and Ctenophora. RESULTS: We have uncovered three MHCII paralogues in the ctenophore species Pleurobrachia pileus. Phylogenetic analyses indicate that the MHCIIa / MHCIIb duplication is more ancient than the divergence between extant metazoan lineages. The ctenophore MHCIIa gene (PpiMHCIIa) has an expression pattern akin to that of "stem cell markers" (Piwi, Vasa...) and is expressed in proliferating cells. We identified two MHCIIb genes that originated from a ctenophore-specific duplication. PpiMHCIIb1 represents the exclusively muscular form of myosin II in ctenophore, while PpiMHCIIb2 is expressed in non-muscle cells of various types. In parallel, our phalloidin staining and TEM observations highlight the structural complexity of ctenophore musculature and emphasize the experimental interest of the ctenophore tentacle root, in which myogenesis is spatially ordered and strikingly similar to striated muscle formation in vertebrates. CONCLUSION: MHCIIa expression in putative stem cells/proliferating cells probably represents an ancestral trait, while specific involvement of some MHCIIa genes in smooth muscle fibres is a uniquely derived feature of the vertebrates. That one ctenophore MHCIIb paralogue (PpiMHCIIb2) has retained MHCIIa-like expression features furthermore suggests that muscular expression of the other paralogue, PpiMHCIIb1, was the result of neofunctionalisation within the ctenophore lineage, making independent origin of ctenophore muscle cells a likely option.     

RNAi-mediated pinoresinol lariciresinol reductase gene silencing in flax (Linum usitatissimum L.) seed coat: Consequences on lignans and neolignans accumulation

RNAi technology was applied to down regulate LuPLR1 gene expression in flax (Linum usitatissimum L.) seeds. This gene encodes a pinoresinol lariciresinol reductase responsible for the synthesis of (+)-secoisolariciresinol diglucoside (SDG), the major lignan accumulated in the seed coat. If flax lignans biological properties and health benefits are well documented their roles in planta remain unclear. This loss of function strategy was developed to better understand the implication of the PLR1 enzyme in the lignan biosynthetic pathway and to provide new insights on the functions of these compounds. RNAi plants generated exhibited LuPLR1 gene silencing as demonstrated by quantitative RT-PCR experiments and the failed to accumulate SDG. The accumulation of pinoresinol the substrate of the PLR1 enzyme under its diglucosylated form (PDG) was increased in transgenic seeds but did not compensate the overall loss of SDG. The monolignol flux was also deviated through the synthesis of 8-5′ linked neolignans dehydrodiconiferyl alcohol glucoside (DCG) and dihydro-dehydrodiconiferyl alcohol glucoside (DDCG) which were observed for the first time in flax seeds.     

New insights on ctenophore neural anatomy: immunofluorescence study in Pleurobrachia pileus (Müller, 1776)

Ctenophores are non-bilaterian animals sharing with cnidarians and bilaterians the presence of sensory receptors, nerve cells, and synapses, absent in placozoans and sponges. Although recent immunofluorescence studies have renewed our knowledge of cnidarian neuro-anatomy, ctenophores have been much less investigated despite their importance to understanding the origin and early evolution of the nervous system. In this study, the neuro-anatomy of the ctenophore Pleurobrachia pileus (Müller, 1776) was explored by whole-mount fluorescent antibody staining using antibodies against tyrosylated -tubulin, FMRFamide, and vasopressin. We describe the morphology of nerve nets and their local specializations, and the organization of the aboral neuro-sensory complex comprising the apical organ and polar fields. Two distinct nerve nets are distinguished: a mesogleal nerve net, loosely organized throughout body mesoglea, and a much more compact “nerve net” with polygonal meshes in the ectodermal epithelium. The latter is organized as a plexus of short nerve cords. This epithelial nervous system contains distinct sub-populations of dispersed FMRFamide and vasopressin immunoreactive nerve cells. In the aboral neuro-sensory complex, our most significant observations include specialized nerve nets underlying the apical organ and polar fields, a tangential bundle of actin-rich fibers (interpreted as a muscle) within the polar fields, and distinct groups of neurons labeled by anti-FMRFamide and anti-vasopressin antibodies, within the apical organ floor. These results are discussed in a comparative perspective.     

A transposon-like structure related to the delta-endotoxin gene of Bacillus thuringiensis.

A DNA segment (Th-sequence) has been found in several strains of Bacillus thuringiensis. This Th-sequence [3 megadaltons (Md)] induces adjacent deletions when it is located in the pAM beta 1 plasmid derived from Streptococcus faecalis. Electron microscopic examination of reannealed single strands of one plasmid (pMT9) carrying such a deletion revealed that the Th-sequence corresponds to a single-stranded loop (2.8 Md) bounded by a short double-stranded stem (less than 0.2 Md). Southern blotting experiments established that in B. thuringiensis the Th-sequence was generally located on the large plasmid which also harbours the gene coding for the delta-endotoxin (crystal protein). Hybridization and heteroduplex analysis of the extrachromosomal DNA from the berliner 1715 strain demonstrated that the crystal gene and the Th-sequence are located in close vicinity on a 42-Md plasmid and that they are separated by a 1.3-Md DNA segment. This DNA segment is repeated in inverted orientation, once immediately adjacent to the Th-sequence and once 1.8 Md beyond the crystal gene. A model for the organization of these DNA sequences inside a transposon-like structure is proposed.