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At least 649 records · Page 36Linked to original sources
PubMed1994

[Genetics of autoimmune diseases].

Strategies for studying the genetics of autoimmune diseases have undergone a considerable evolution during the last years, especially due to molecular biology techniques and to systematic genome studies. Genetic factors account for 20 to 40% of the risk, and environmental elements play a major role. The major histocompatibility complex comprising HLA genes remains the immunogenetic system most studied and most closely associated with various autoimmune diseases. These associations are mainly observed with HLA class II genes polymorphisms; the precise knowledge of their structure has allowed to define HLA sequence polymorphisms which are themselves risk markers: specific combinations of HLA-DQA and DQB alleles in insulin-dependent diabetes mellitus or a given DR, DQ haplotype for multiple sclerosis. No strong association with HLA-DP has been demonstrated. In all cases the genes involved have a normal structure and the disease is secondary to the combination of a given set of genes with environmental factors. The present knowledge of insulin-dependent diabetes mellitus and multiple sclerosis genetics is rather advanced. Other genes of the HLA region might also be involved in the genetic susceptibility. Results about other immunogenetic systems (T cell receptor genes or heavy chain immunoglobulin genes) are still contradictory but no major gene for autoimmune susceptibility seems to exist in these regions; however autoimmune diseases are under polygenic control; susceptibility genes shared between different diseases often occurring within the same families (Graves' disease and insulin-dependent diabetes mellitus) and genes specific for a given disease (insulin gene region in diabetes) both exist. The present rapid progress in this area is due to the use of highly polymorphic markers randomly distributed across the genome (microsatellites being most informative) and that of animal models: the list of "candidate genes or regions" potentially involved in the genetics of autoimmune diseases is enlarging; the development of coordinated epidemiological studies of molecular genetics along with the sharing of biological resources between different teams allow to build up powerful informative studies which will confirm or refute those "candidates". However, once the list of genes involved is established their mechanism of action will still take time to elucidate.

Autoimmune Diseases↗
PubMed1993

[Genetics and molecular biology of neurinoma and meningioma].

Tumorigenesis is caused by abnormal proliferation of cells that escape regulatory mechanisms. Most of the molecular events leading to the formation of tumors are still largely unknown. In this paper, experimental data supporting a causative role for cellular genes, termed oncogenes, in the formation of tumors of the nervous system are reviewed. Two types of oncogenes are described: dominant oncogenes, characterized by the fact that one abnormal copy of the gene is sufficient to induce tumorigenesis, and recessive oncogenes which require the inactivation of both copies of the gene to lead to tumor formation. The role of recessive oncogenes in tumorigenesis of the nervous system is illustrated by molecular studies of meningiomas and neurinomas. The mutation of one, and perhaps two loci on chromosome 22, has indeed been shown to be most probably the causative molecular event in the growth of these two tumors when they occur either in their sporadic form, or in neurofibromatosis type 2. All the available data support the proposition of systematically analyzing a large number of tumors to eventually correlate clinical phenotype and evolution, to the genetic abnormalities observed. Furthermore, the understanding of the normal and pathological function of oncogenes should lead to future therapeutical improvements.

Adult↗
PubMed2006

Evolutionary conservation of protein backbone flexibility.

Internal protein dynamics is essential for biological function. During evolution, protein divergence is functionally constrained: properties more relevant for function vary more slowly than less important properties. Thus, if protein dynamics is relevant for function, it should be evolutionary conserved. In contrast with the well-studied evolution of protein structure, the evolutionary divergence of protein dynamics has not been addressed systematically before, apart from a few case studies. X-Ray diffraction analysis gives information not only on protein structure but also on B-factors, which characterize the flexibility that results from protein dynamics. Here we study the evolutionary divergence of protein backbone dynamics by comparing the C(alpha) flexibility (B-factor) profiles for a large dataset of homologous proteins classified into families and superfamilies. We show that C(alpha) flexibility profiles diverge slowly, so that they are conserved at family and superfamily levels, even for pairs of proteins with nonsignificant sequence similarity. We also analyze and discuss the correlations among the divergences of flexibility, sequence, and structure.

Amino Acid Sequence↗
PubMed1981

Allometry of primate hair density and the evolution of human hairlessness.

Allometric analyses of hair densities in 23 anthropoid primate taxa reveal that increasingly massive primates have systematically fewer hairs per equal unit of body surface. Considering the absence of effective sweating in monkeys and apes, the negative allometry of relative hair density may represent an architectural adaptation to thermal constraints imposed by the decreasing ratios of surface area to volume in progressively massive primates. Judging by estimates of body volume, denudation of the earliest hominids should have progressed to a considerable extent prior to their shift from a forest to a grassland habitat during the Pliocene. We propose that, lacking a reflective coat of hair, the exploitation of eccrine sweating emerged as the primary mechanism for adaptation to the increased heat leads of man's new environment and permitted further reduction of the remnant coat to its present vestigial condition.

Animals↗
PubMed1989

Some aspects of the organization and evolution of the genetic code.

In this paper, I define a measure of the relative position of each amino acid in the genetic code by means of a 21-dimensional vector describing its potential for mutation, in a single step, to each of the other amino acids, or to a chain termination codon. This measure allows us to make a systematic investigation of the type and number of the physicochemical properties of the amino acids that were involved in evolution. The polar character and size of amino acids are identified in this analysis as properties that played a leading role in the evolutionary history of the genetic code. The application of cluster analysis and discriminant analysis reveals the characteristics of the structural organization of the genetic code. Finally, I suggest the existence of a relationship between the molecular weight of the amino acids and the number of synonymous codons.

Amino Acids↗
PubMed1997

[Status epilepticus: indications for emergency EEG].

EEG is a major tool in convulsive status epilepticus. Several techniques may be used, including conventional or digitized EEG using 4, 8, 10 or 16 channels, continuous monitoring with or without simultaneous video recording, and cerebral function monitor. During the first phase, in the emergency ward, EEG may be useful in severe convulsive status epilepticus to assess further evolution and/or prognosis. However, rapid control of seizure at this phase is the primary goal, and optimization of EEG availabilities may lead to more systematic indications. After adequate control of seizures, EEG is mandatory in the following situations: i) a difficult-to-control convulsive status epilepticus, with a high risk of subsequent evolution towards subtle status epilepticus; ii) a resistant status epilepticus which needed high dose of sedatives drugs and/or curarization, to evaluate the level of anaesthesia and to watch for recurrence of epileptiform abnormalities; iii) a permanent, unexplained impairment of consciousness which followed an apparently successful treatment, to detect non convulsive status epilepticus; 4. a doubtful clinical diagnosis, to confirm pseudo-status epilepticus.

Electroencephalography↗
PubMed1997

Intron open reading frames as mobile elements and evolution of a group I intron.

Group I introns are proposed to have become mobile following the acquisition of open reading frames (ORFs) that encode highly specific DNA endonucleases. This proposal implies that intron ORFs could behave as autonomously mobile entities. This was supported by abundant circumstantial evidence but no experiment of ORF transfer from an ORF-containing intron to its ORF-less counterpart has been described. In this paper we present such experiments, which demonstrate the efficient mobility of the mitochondrial nad1-i4-orf1 between two Podospora strains. The homing of this mobile ORF was accompanied by a bidirectional co-conversion that did not systematically involve the whole intron sequence. Orf1 acquisition would be the most recent step in the evolution of the nad1-i4 intron, which has resulted in many strains of Podospora having an intron with two ORFs (biorfic) and four splicing pathways. We show that two of the splicing events that operate in this biorfic intron, as evidenced by PCR experiments, are generated by a 5'-alternative splice site, which is most probably a remnant of the monoorfic ancestral form of the intron. We propose a sequential evolution model that is consistent with the four organizations of the corresponding nad1 locus that we found among various species of the Pyrenomycete family; these organizations consist of no intron, an intron alone, a monoorfic intron, and a biorfic intron.

Alternative Splicing↗
PubMed2005

Evolution of surface morphologies in multivariant assemblies of surface-tethered diblock copolymers after selective solvent treatment.

We study systematically the topography behavior of PHEMA-b-PMMA block as a function of the PHEMA and PMMA block lengths after selectively collapsing the top (PMMA) block by using surface-anchored assemblies of poly(2-hydroxyethyl methacrylate-b-methyl methacrylate), PHEMA-b-PMMA, block copolymer with orthogonally varying lengths of each block. Our experimental results are in excellent qualitative agreement with topology diagrams predicted by self-consistent field calculations of Zhulina and co-workers.

Polyhydroxyethyl Methacrylate↗
PubMed2001

Virtual anthropology: the digital evolution in anthropological sciences.

The discovery and explanation of differences among organisms is a major concern for evolutionary and systematic biologists. In physical anthropology, the discrimination of taxa and the qualitative and quantitative description of ontogenetic or evolutionary change require, of course, the analysis of morphological features. Since the 1960s, a remarkable amount of fossil material was excavated, some of it still awaiting a detailed first analysis, some of it requiring re-examination by more developed methods. While the fossil record grew continuously, a revolution in anthropological research took place with advances in computer technology in the 1980s: a handful of innovative researchers working in specialized anthropology laboratories or medical departments developed the methodological inventory needed to extract critical information from subjects in vivo and from fossilized remains. A considerable part of this information is preserved in the physically heretofore inaccessible interior of anatomical structures. Virtual Anthropology (VA) is a means of making them visible and measurable. Thus, VA also allows access to 'hidden' landmarks; in addition, the large number of semilandmarks accessible on the form enhances the power of Geometric Morphometrics analysis. Furthermore, the density information in volume data allows manipulations such as segmentation, impossible with the real, physical object. Moreover, metric body measurements generally, and cranial measurements specifically, are also an important source of information for the analysis of the ontogenetic development of the skeletal system, and--last but not least--for clinical use (e.g., operation planning, operation simulation, prosthetics). Thus, there developed a fruitful interdisciplinary cooperation between statistics, medicine, and physical anthropology.

Anthropology, Physical↗
PubMed1990

[Should systematic bone scintigraphy be carried out on breast cancer patients with small tumors?].

Bone metastases are frequent in the evolution of breast cancer. Bone scan is the best method for early detection. At initial presentation the frequency of bone metastases is low, and it is usefulness to recommend this exam except for old people or patients with risks factors. During the follow-up, the utility of repeated bone scan is discussed. For the majority of authors, it may be reserved for symptomatic patients or when biological modifications appeared. The follow-up of these patients must be essentially clinical. This strategy delay the diagnosis of bone metastases of only a few weeks; and it don't seem to affect the prognosis of these patients.

Age Factors↗
PubMedDate not supplied

[Bipolarity correlated factors in major depression: about 155 Tunisian inpatients].

The distinction between the depressive troubles according to their inclusion in bipolar disorders or in recurrent depressive disorders offers an evident practical interest. In fact, the curative and mainly the preventive treatment of these troubles are different. So it is necessary to identify the predictive factors of bipolar development in case of inaugural depressive episode. In 1983, Akiskal was the first who identified those factors: pharmacological hypomania, puerperal depression, onset at early age (<25 years), presence of psychotic characteristics, hypersomnia and psychomotor inhibition. Through this study, the authors try to compare the epidemiological, clinical and evolution characteristics of major depression in bipolar disorders to recurrent depressive disorders in order to indicate the correlated factors with bipolarity. It is a retrospective and comparative study based on about 155 inpatients for major depressive episode during the period between January 1994 and December 1998. These patients were divided into two groups according the DSM IV criteria: bipolar group (96 patients) and recurrent depressive group (59 patients). Both groups were compared according to socio-demographic data, life events in childhood, personal and family history, clinical and evolution characteristics of the index depressive episode. The predictive factors proposed by Akiskal were systematically examined. It was found out that the following factors were correlated with bipolarity: high rate of separation and divorce (17.7% versus 5.1%; p=0.02), family history of psychiatric disorders (56.3% versus 35.6%; p=0.012) especially bipolar ones (29.2% versus 3.4%; p=0,00008), onset at early age (mean age of onset: 24.8 8.2 years versus 34.1 12.6 years; p=0.000004), number of affective episode significantly more frequent (mean 3.6 versus 2.5; p=0.03), sudden onset of depressive episode (44.8% versus 15.9%; p=0.0003) and presence of psychotic characteristics (69.8% versus 16.7%; p=0.0001) catatonic characteristics (37.3% versus 20.3%; p=0.03), hypersomnia (51% versus 20.3%; p=0.03) and psychomotor inhibition (83.3% versus 42.4%; p=0.00007). Negatively correlated factors of bipolar depression were: somatic comorbidity such as diabetes, hypertension and rhumatismal diseases (12.5% versus 28.8%; p=0.012) and association with dysthymic disorders (2.2% versus 12.1%; p=0.029). No correlation was found between bipolarity and life events in childhood, seasonal character, alcoholic dependence and suicide attempt. Concerning the validity of predictive factors of bipolarity proposed by Akiskal, we found: history of bipolar disorders (Sensibility: 29.2%, specificity: 96.6%, Positive Predictive Value (PPV): 93%), hypersomnia (Sensibility: 51%, specificity: 80%, PPV: 80%), onset before the age of 25 years (Sensibility: 62.5%, specificity: 70%, PPV: 77%), psychomotor inhibition (Sensibility: 83.3%, specificity 58%, PPV: 76%), and psychotic characteristics (Sensibility: 69.8%, specificity: 62.7%, PPV: 75%). In spite of methodological differences, our results tallied with the other studies. We focus on the importance of the bipolar family history criterion, which has the highest PPV, and the limits of psychotic characteristics criterion which has the lowest PPV. This may be explained by the frequency of these characteristics of affective disorders in our cultural context. The association of the hypersomnia and psychomotor inhibition in one criterion in order to increase their diagnostic power. Our study helps us to identify the factors that would predict the bipolar evolution of a depressive episode allowing the use of specific treatment and ensuring the improvement of prognostic.

Adult↗
PubMed1993

On the origin of mitosing cells. 1967

A theory of the origin of eukaryotic cells ("higher" cells which divide by classical mitosis) is presented. By hypothesis, three fundamental organelles: the mitochondria, the photosynthetic plastids and the (9+2) [9(2)+2] basal bodies [kinetosomes] of flagella [undulipodia] were themselves once free-living (prokaryotic) cells. The evolution of photosynthesis under the anaerobic [anoxic] conditions of the early atmosphere to form anaerobic bacteria, photosynthetic bacteria and eventually blue-green algae (and protoplastids) is described. The subsequent evolution of aerobic metabolism in prokayotes to form aerobic bacteria (protoflagella [undulipodia] and protomitochondria) presumably occurred during the transition to the oxidizing atmosphere. Classical mitosis evolved in protozoan-type cells millions of years after the evolution of photosynthesis. A plausible scheme for the origin of classical mitosis in primitive amoeboflagellates [amoebomastigotes] is presented. During the course of the evolution of mitosis, photosynthetic plastids (themselves derived from prokaryotes) were symbolically acquired by some of these protozoans to form the ["eukaryotic" deleted] algae and the green plants. The cytological, biochemical and paleontological evidence for this theory is presented, along with suggestions for further possible experimental verification. The implications of this scheme for the systematics of the lower [smaller] organisms is discussed.

Animals↗