The sequencing of several genomes from each of the three domains of life (Archaea, Bacteria and Eukarya) has provided a huge amount of data that can be used to gain insight about early cellular evolution. Some features of the universal tree of life based on rRNA polygenies have been confirmed, such as the division of the cellular living world into three domains. The monophyly of each domain is supported by comparative genomics. However, the hyperthermophilic nature of the 'last universal common ancestor' (LUCA) is not confirmed. Comparative genomics has revealed that gene transfers have been (and still are) very frequent in genome evolution. Nevertheless, a core of informational genes appears more resistant to transfer, testifying for a close relationship between archaeal and eukaryal informational processes. This observation can be explained either by a common unique history between Archaea and Eukarya or by an atypical evolution of these systems in Bacteria. At the moment, comparative genomics still does not allow to choose between a simple LUCA, possibly with an RNA genome, or a complex LUCA, with a DNA genome and informational mechanisms similar to those of Archaea and Eukarya. Further comparative studies on informational mechanisms in the three domains should help to resolve this critical question. The role of viruses in the origin and evolution of DNA genomes also appears an area worth of active investigations. I suggest here that DNA and DNA replication mechanisms appeared first in the virus world before being transferred into cellular organisms.
Protein interactions within a multimolecular complex can result in information and energy transfer between proteins. This can lead in turn to the emergence of novel functions of some proteins of the complex. Various examples of this situation can be found in the scientific literature. This is probably the case for prion protein, chloroplast phosphoribulokinase bound to glyceraldehyde phosphate dehydrogenase, Ras system, and pancreatic lipase bound to biomembranes, to cite but a few. Any enzyme reaction, or enzyme reaction network, carries Shannon entropy and information. On contrary to genome entropy, the entropy of enzyme reactions and metabolic sequences is sensitive to 'external' signals, such as substrate, effector and proton concentrations. Complex structural organization of the cell is associated with a higher entropy content, and one can calculate the gain of entropy and information due to integration and complexity. One may conclude from this brief analysis that the informational content of a living cell is much larger than that of its genome.
Hepatitis C virus (HCV) is of major social, medical and economic importance. The prevalence of HCV is approximatively 1% in most developed countries, and much higher in developing countries. HCV infection is the second major cause, after hepatitis B virus infection, for the generation of chronic liver disease and hepatocellular carcinoma. To date, the only reliable model for the study of HCV infection is the chimpanzee. Indeed, there is no robust in vitro infection system, yet. There is thus an urgent need for such an in vitro infection system in order to evaluate therapeutic agents. Here, a process is provided for infecting hepatocyte cell lines with hepatitis C virus in vitro. It is strongly suggested that cell-bound lipoproteins are playing a crucial role during the infection process. In order to obtain a robust infection, the cell-bound lipoproteins have first to be removed from their cellular receptor prior to the addition of viral inocula originating from human sera, the latter being made originally of a virus-lipoprotein complex.
Effects of RU 486 (10 mg(.)kg(-1), per.os) were assessed at mid-pregnancy in the rat. One hour after RU 486 treatment, myometrial electrical activity stayed low. It increased from the 3rd hour after administration of RU 486 and a perfect synchronization of the bursts of the action potentials was observed from the 6th h to the 24th h. Tissular steroid hormones and PGF(2 alpha) evaluated at hour 6 after RU 486 administration, showed a decrease of progesterone concentrations in both myometrium and uterus. Estradiol levels decreased in uterus whereas, PGF(2 alpha) levels increased in both myometrium and uterus. These results show for the first time that RU 486 strongly increases the myometrial electrical activity in the rat at mid-pregnancy. This action was closely related to E-2, P-4 and PGF(2 alpha) concentrations. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
A human being or person cannot be reduced to a set of human genes, or human genome. Genetic essentialism is wrong, because as a person the entity should have self-conscious and social interaction capacity which is grown in an interpersonal relationship. Genetic determinism is wrong too, the relationship between a gene and a trait is not a linear model of causation, but rather a non-linear one. Human genome is a complexity system and functions in a complexity system of human body and a complexity of systems of natural/social environment. Genetic determinism also caused the issue of how much responsibility an agent should take for her/his action, and how much degrees of freedom will a human being have. Human genome research caused several conceptual issues. Can we call a gene 'good' or 'bad', 'superior' of 'inferior'? Is a boy who is detected to have the gene of Huntington's chorea or Alzheimer disease a patient? What should the term 'eugenics' mean? What do the terms such as 'gene therapy', 'treatment' and 'enhancement' and 'human cloning' mean etc.? The research of human genome and its application caused and will cause ethical issues. Can human genome research and its application be used for eugenics, or only for the treatment and prevention of diseases? Must the principle of informed consent/choice be insisted in human genome research and its application? How to protecting gene privacy and combating the discrimination on the basis of genes? How to promote the quality between persons, harmony between ethnic groups and peace between countries? How to establish a fair, just, equal and equitable relationship between developing and developed countries in regarding to human genome research and its application?
The vegetation and physical and chemical characteristics of the water and sediment in ten temporary pools submitted to various anthropogenic disturbance were studied in Morocco over two hydrological cycles (1997-1998 and 1998-1999). Results of multivariate and parametric analyses show that disturbance has a significant impact on water and sediment. Agriculture in the catchment resulted in higher levels of N and the use of detergent to higher levels of phosphorus in both water and sediment. Mineral extraction resulted in higher depth and longer duration of flooding. Vegetation characteristics were better correlated to hydrology (water depth, duration of flooding) than to nutrient variables. These results suggest that although agriculture in the catchment contribute in modifying the sediment characteristics, the impact on vegetation and its conservation value is limited. However, care should be taken of the long-term effects of agriculture through cumulative effects and of the possible consequences of changing the agricultural practices. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
Most prokaryotic genomes display strand compositional asymmetries, but the reasons for these biases remain unclear. When the distribution of gene orientation is biased, as it often is, this may induce a bias in composition, as codon frequencies are not identical. We show here that this effect can be estimated and removed, and that the residual base skews are the highest at third base codon positions and lower at first and second positions. This strongly suggests that compositional asymmetries result from 1) a replication-related mutational bias that is filtered through selective pressure and/or from 2) an uneven distribution of gene orientation. In most cases, the mutational bias alters the codon usage and amino acid frequencies of the leading and the lagging strand. However, these features are not ubiquitous amongst prokaryotes, and the biological reasons for them remain to be found.
The muscle fiber fascicles of the temporo-masseter complex of the cat were minutely dissected. Some heads were embedded in paraffin while others were put into methyl-methacrylate resin and sections were made. The results of this anatomical study demonstrate that this complex consists of the masseter muscle, the temporal muscle and two well individualized transitional fascicles: the maxillomandibularis and zygomato-comandibularis muscles. The masseter and temporal muscles are composed of individualized compartments in which the orientation and aponeuroses of the fibers of which they are composed differ with regard to the centric occlusion plane. The masseter muscle consists of a superficial fascicle made up of two layers, an intermediate fascicle, and a deep fascicle composed of two layers. The temporal muscle consists of one anterior orbital part and one posterior temporal part. This structure is in accordance with the mammalian archetype described by Gaspard and Saban. These findings should lead towards a homology-based nomenclature founded on comparative anatomy studies of mammalian species. Such a classification would permit the comparison of results obtained from physiological and histochemical studies of these complex muscle fibers when they are published by different researchers.
An ultrastructural study of Weddellomyces epicallopisma (ascomata wall, asci, ascospores and vegetative hyphae), the first done on the family Dacampiaceae, confirms most of the observations made in light microscopy. Moreover it shows that ascospores are provided with an endospore (not visible in light microscope) and that the structure of the ascospore septum is more complex. The similarity of the wall structure between the ascospore and the hyphoid appendages, developed on the upper part of the ascoma, is emphasized.
Pollination and fertilization are key steps leading to seed and fruit formation. To obtain genes involved in pollination and fertilization in rice, an RNA fingerprinting technique, cDNA-AFLP (amplified fragment length polymorphism), was used to generate transcript profiles related to pollination. Of 15 000 cDNA fragments inspected, 2 100 showed altered expression in the pollinated pistil, of which about 1/5 were up-regulated (URP) and the rest down-regulated (DRP), suggesting that gene repression is a predominant mode of gene regulation in the pollinated pistil. Over 200 URP genes were sequenced and databank searches revealed that 70% of them represented previously unnoticed rice genes. DNA blot analysis of 20 URP genes detected no restriction fragment length polymorphisms (RFLP) between two relatively distant rice varieties, suggesting that the URP genes are highly conserved and likely play important roles in pollination and fertilization. Furthermore, two genes, URP47 and URP63, probably encoding an ADP-ribosylation factor and a membrane transporter, respectively, in relation to pollination were discussed. (C) 2001 Academie des Sciences/Editions scientifiques et medicales Elsevier SAS.
Carbon isotope discrimination (delta) has been proposed as a good criterion for transpiration efficiency and grain yield improvement. Its measurement, however, remains very expensive. Ash content (ma) has been proposed as an alternative criterion for delta in bread wheat and barley. The aims of this study were (i) to analyse the relationships between delta and mineral composition in different durum wheat plant parts and (ii) to compare the variation of these traits between landraces and improved varieties from different geographic origins. For this purpose, delta, ma, and composition in four minerals (K, Mg, P and Si) were assessed in flag leaves and awns at anthesis, and in mature grains of ten durum wheat genotypes grown under rainfed Mediterranean conditions. The three plant parts differed significantly for the measured traits. Significant correlations were noted between delta and ma in the flag leaf and in the grain. Silicon content in flag leaves and potassium content in awns were also positively related to delta of the considered plant part. The coefficient of correlation between delta and ma was generally higher than that observed between individual mineral content and delta, suggesting that ma is the better alternative criterion for delta. In addition, grain yield was related to grain delta and both ma and potassium content in awns. Harvest index was correlated with delta and ma of grain and flag leaf. These results emphasised that ma values in flag leaf and grain represent the efficiency of carbon partitioning to the grain. Improved varieties showed higher delta and ma values than landraces. Differences between Middle-East and West Mediterranean genotypes for the measured traits were also presented and discussed.
Lipid metabolism of the endomycorrhizal fungus: Glomus intraradices. The use of monoxenic cultures of the obligately biotrophic vesicular arbuscular fungus Glomus intraradices now permits investigation of the lipid metabolism of this organism. In bicompartmental culture plates, sporulating extraradical hyphae can be obtained, totally free of roots, and then provided with C-14-acetate as lipid precursor. Three experimental stages were studied: i) stage A, symbiotic stage corresponding to the fungus still attached to the host plant roots, ii) stage B, consisting of the fungus detached from the host roots, iii) stage C, germinating spores. In each case, the fungus proved to be able to synthesise its own lipids: 1,2- and 1,3-diacylglycerols, triacylglycerols, phospholipids, sterols and free fatty acids, de novo. Lipid metabolism varied with the experimental conditions. Phospholipid synthesis was intensive in germinating spores. Thus the obligately biotrophic status of this fungus cannot be explained by a deficiency in synthesis of these various lipid classes. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
The aim of this study was to determine the dioecious or monoecious condition of Fitzroya cupressoides and Pilgerodendron uviferum. The study area lies west of the Nahuel Huapi National Park in northern Patagonia (Argentina), where these species form mixed stands. One hundred individuals of each species were studied over three successive years. The nature and position in the crown of their reproductive organs were recorded. Results showed that both species are dioecious. This feature has been confirmed on trees of these species growing in other sites within their natural distribution area in Argentina and Chile.
We used a simple quadrat analysis to globally categorise the spatial distribution of Drosophila melanogaster individuals. Individuals were spatially aggregated and this was not only due to sexual attraction. This aggregation seemed to be maintained during dispersal, hence explaining the great variability of this behaviour observed in our work and by other authors. Thus, individuals are expected to arrive as small groups into a new patch. This may induce costs through competition and benefits by ensuring the presence of reproductive mates and/or if there is a phenomenon of local resource enhancement by the presence of conspecifics, hence influencing the evolution of dispersal.
Two new diatom species, Haslea salstonica and Haslea pseudostrearia are described in light and electron microscopy and compared with two well-known members of Haslea. Scanning electron microscope observations confirm that the new species belong to the genus Haslea. This study extends previous observations on the genus, particularly with respect to the development of a pseudostauros. The characteristic features of the genus are discussed briefly.
Viroids are subviral plant pathogens at the frontier of life. They are solely composed by a single-stranded circular RNA of 246-401 nt with a compact secondary structure. Viroids replicate autonomously when inoculated into their host plants and incite, in most of them, economically important diseases. In contrast to viruses, viroids do not code for any protein and depend on host enzymes for their replication, which in some viroids occurs in the nucleus and in others in the chloroplast, through a rolling-circle mechanism with three catalytic steps. Quite remarkably, however, one of the steps, cleavage of the oligomeric head-to-tail replicative intermediates to unit-length strands, is mediated in certain viroids by hammerhead ribozymes that can be formed by their strands of both polarities. Viroids induce disease by direct interaction with host factors, the nature of which is presently unknown. Some properties of viroids, particularly the presence of ribozymes, suggest that they might have appeared very early in evolution and could represent 'living fossils' of the precellular RNA world that presumably preceded our current world based on DNA and proteins.
The present study points to morpho-anatomical features that allow vegetarian but mainly frugivorous turacos to fill at best their specific feeding requirements. Mechanisms are analysed which the bird can use to detach a fruit and avoid it rolls out of the bill. It also examined how vegetable items can be processed particularly when they have to be cut, and what can facilitate their ingestion particularly when they are fruits that to be swallowed entirely and are large or have dry or fibrous skin or flesh. The skeletal and muscular anatomy of the bill and hyoid apparatus is described in details and illustrated. The particularly short and stout bill coupled with a relatively simple system of aponevroses of the adductors reflects a trade-off between two important jaw functional requirements: huge efforts for clamping, and a wide opening for plucking, processing and swallowing relatively large fruit. The clearly oblique orientation of the modified outer adductor seems an adaptation to the detachment of fruits. The os uncinatum, particularly developed in this bird family, is interpreted as maintaining transversal stability, particularly when jaws act as a pair of scissors. Most food items being processed near the base of the bill, mechanism have been developed which contribute to overcome the risk of breakage at the level of the prokinetic hinge because of a vertically oriented force there.
The objective of this study was to analyse the development of the foetal pelvis in order to define normal anatomic reference values as a function of gender and gestational age. The study population included 500 stillborn foetuses between the gestational ages of 18 and 41 weeks. Those foetuses without known demographic histories were strictly excluded. For each case studied, an AP radiograph was performed with the following parameters measured by two independent observers: pelvic width, inter-iliac width, inter-sciatic nodes, inter-pubic width and bi-ischial width. The correlation between these radiographic measurements and the gestational age as well as the gender was analysed. The result indicated that the inter-ischiatic distance is significantly greater in the female foetus after the 26-27th week of gestation (P < 0.0062). Standard growth for the female and the male foetal pelvis is proposed with potential application in the study of normal and pathological development of the foetus. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
A comparative study of radial growth and biomass between multi-stemmed trees with variable number of stems and single-stemmed trees was carried out to better understand determinism and organisation of multicaulis structure of a juniper species (Juniperus thurifea L.) growing in high Mediterranean mountains (High Atlas, Morocco). It appears that all the stems of the same tree have similar ages and so simultaneous development. Their mean annual radial increments show significant differences because of probable competition for water and nutrient supply and obvious physical competition for space. The multistemmed trees characterized by low number of stems have the same mean annual radial growth as single-stemmed trees and more generally all multistemmed junipers have a higher biomass. The multicaulis structure of Juniperus thurifera thus could be considered as an adaptation to severe environment, characterized not only by hard topographical, edaphic and climatic conditions, but by strong human pressure too. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
