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Results for “somatic evolution”

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At least 109 records · Page 6Linked to original sources
PubMed1990

Floral homeotic mutations produced by transposon-mutagenesis in Antirrhinum majus.

To isolate and study genes controlling floral development, we have carried out a large-scale transposon-mutagenesis experiment in Antirrhinum majus. Ten independent floral homeotic mutations were obtained that could be divided into three classes, depending on whether they affect (1) the identity of organs within the same whorl; (2) the identity and sometimes also the number of whorls; and (3) the fate of the axillary meristem that normally gives rise to the flower. The classes of floral phenotypes suggest a model for the genetic control of primordium fate in which class 2 genes are proposed to act in overlapping pairs of adjacent whorls so that their combinations at different positions along the radius of the flower can specify the fate and number of whorls. These could interact with class 1 genes, which vary in their action along the vertical axis of the flower to generate bilateral symmetry. Both of these classes may be ultimately regulated by class 3 genes required for flower initiation. The similarity between some of the homeotic phenotypes with those of other species suggests that the mechanisms controlling whorl identity and number have been highly conserved in plant evolution. Many of the mutations obtained show somatic and germinal instability characteristic of transposon insertions, allowing the cell-autonomy of floral homeotic genes to be tested for the first time. In addition, we show that the deficiens (def) gene (class 2) acts throughout organ development, but its action may be different at various developmental stages, accounting for the intermediate phenotypes conferred by certain def alleles. Expression of def early in development is not necessary for its later expression, indicating that other genes act throughout the development of specific organs to maintain def expression. Direct evidence that the mutations obtained were caused by transposons came from molecular analysis of leaf or flower pigmentation mutants, indicating that isolation of the homeotic genes should now be possible.

DNA Transposable Elements↗
PubMed1997

Neurophysiological evaluation of sexual dysfunction in familial amyloidotic polyneuropathy--Portuguese type.

Familial amyloidotic polyneuropathy (FAP)--Portuguese type, is an autosomal dominant polyneuropathy related with an abnormal transthyrretin (TTR Met 30). In males, the first complaint can be sexual dysfunction. Fifteen FAP patients, mean age 37 +/- 7.7 years, mean disease duration 5.2 +/- 2.2 years, all males, complaining of sexual dysfunction were studied with pudendal evoked potentials (PEP), bulbocavernous reflex (BCR) and sympathetic skin response (SSR). PEP and BCR reflect the central somatosensory pathways and sacral arch functioning; SSR relates with autonomic pathways. The aims of this study were: to correlate clinical and EMG scores with somatic and autonomic fibres involvement; to evaluate the timing of somatic and autonomic nerves lesion in disease evolution. Results showed: that PEP and BCR abnormalities have a statistically significant correlation with clinical and EMG scores; abnormal SSR in the plant precede other clinical or EMG abnormalities in the present study.

Adult↗
PubMed2026

Induced pluripotent stem cell reprogramming: methodological evolution and challenges in clinical translation.

Cell reprogramming can transform somatic cells into induced pluripotent stem cells providing a platform for patient-specific disease modeling, drug screening and regenerative medicine research. Since the advent of OKSM-mediated reprogramming, the system of technical approaches has evolved continuously - from integrated viral vectors to non-integrated episomal systems and, more recently, chemical reprogramming and CRISPR approaches. The simultaneous advances in single-cell multi-omics, biomaterials engineering, and artificial intelligence have further refined the controllability and precision of the reprogramming process. Despite these innovations, problems persist that hinder clinical translation: incomplete epigenetic resetting, ongoing clonal heterogeneity, genomic instability in long-term culture, and the lack of standardized Good Manufacturing Practice protocols for large-scale manufacturing. This review summarizes the trajectory of iPSC reprogramming technologies, with special emphasis on the translational applicability of each modality. We evaluated viral and nonviral delivery systems, chemical reprogramming, strategies that aid gene editing, and emerging engineering platforms, including microfluidics, smart biomaterials, and artificial-intelligence-driven process optimization. We further identify the core "translational triltrilas", namely, the inherent tradeoffs between security, homogeneity, and scalability, and propose a comprehensive strategy to overcome these bottlenecks. By linking basic mechanistic understandings with industrial and regulatory considerations, this review aims to provide a route for transitioning iPSC technology from a laboratory tool to a clinically viable manufacturing platform.

clinical translation↗
PubMedDate not supplied

[Refractory depression: therapeutic alternatives].

A group of 89 patients admitted to the Psychiatric Unit of a General Hospital, with diagnosis of depression according to ICD-9 criteria and randomly chosen were studied. 26 of them (29.2%) were resistant depressions and 63 (7.82%) responded to treatment. Both groups were composed retrospectively in order to analyse resistance or lack of response to a first treatment with tricyclic or tetracyclic antidepressants in effective dosages. We considered: the personality type; the associated somatic pathology; prolonged social stress; period of evolution of the disorder; previous treatments; type of disorder uni or bipolar; familial morbidity; diagnosis reconsideration; analysis of therapeutic compliance; side effects and intolerance. We observed a statistically significant difference with regard to prophylactic treatment (38.4% resistant versus 98.3% non-resistant, p less than 0.0001); a greater suspicion of psycho-organicity in the resistant group (p less than 0.05); a longer interval of time for the resistant group between the beginning of the disorder and the beginning of treatment in our service (F: 1.45, t: 2.58, p less than 0.01). The alternatives used with our patients are analysed and we propose schedules for tackling this kind of problem.

Antidepressive Agents↗
PubMed1996

Retention of unmethylated CpG island alleles in human diploid fibroblast x fibrosarcoma hybrids expressing high levels of DNA methyltransferase.

The mechanisms underlying ectopic methylation of CpG islands in neoplastic cells are poorly understood. One determinant may be the increased expression of DNA methyltransferase (DNA MTase) observed frequently in neoplastic cells. To evaluate the role of DNA MTase overexpression in aberrant CpG island methylation, we assessed methylation of fibroblast-derived CpG islands in human diploid fibroblast x fibrosarcoma hybrid cell lines. Each of six independently derived, immortalized hybrid cell lines exhibited a high level of DNA MTase expression, comparable to that of the fibrosarcoma parental line. The methylation status of five CpG island loci, each of which was methylated extensively in the fibrosarcoma parental cells but not in the fibroblasts, was then determined in the hybrid cell lines. The patterns of methylation were consistent and highly locus dependent among the hybrid lines. Unmethylated alleles were retained stably at three loci. The parental origin of alleles could be determined at two other loci in the hybrid cells. Whereas no methylation of parental fibroblast-derived alleles of the HIC-1 locus was noted in hybrid cell lines, a marked increase in methylation of fibroblast-derived alleles of the estrogen receptor was observed in all hybrid cell lines. Therefore, despite high-level DNA MTase expression, widespread loss of unmethylated CpG islands was not observed in the hybrid cell lines. The nonrandom pattern of increased CpG island methylation in the hybrid cell lines suggests that locus-specific features and/or clonal selection, and not just DNA MTase expression, affect the evolution of ectopic methylation in neoplastic cells. Somatic cell hybrids may provide useful models for studying aberrant epigenetic events in neoplastic cells.

Alleles↗
PubMed1995

Genetic conflict and evolution of mammalian X-chromosome inactivation.

The existence of parentally imprinted gene expression in the somatic tissues of mammals and plants can be explained by a theory of intragenomic genetic conflict, which is a logical extension of classical parent-offspring conflict theory. This theory unites conceptually the phenomena of autosomal imprinting and X-chromosome inactivation. We argue that recent experimental studies of X-chromosome inactivation and androgenetic development address previously published predictions of the conflict theory, and we discuss possible explanations for the occurrence of random X-inactivation in the somatic tissues of eutherians.

Animals↗
PubMed1997

Codon bias and plasticity in immunoglobulins.

Immunoglobulin genes experience Darwinian evolution twice. In addition to the germline evolution all genes experience, immunoglobulins are subjected, upon exposure to antigen, to somatic hypermutation. This is accompanied by selection for high affinity to the eliciting antigen and frequently results in a significant increase in the specificity of the responding population. The hypermutation mechanism displays a strong sequence specificity. Thus arises the opportunity to manipulate codon bias in a site-specific manner so as to direct hypermutation to those parts of the gene that encode the antigen-binding portions of the molecule and away from those that encode the structurally conserved regions. This segregation of mutability would clearly be advantageous; it would enhance the generation of potentially useful variants while keeping mutational loss to acceptably low levels. But it is not clear that the advantage gained would be large enough to produce a measurable effect within the background stochasticity of the evolutionary process. I have performed a pair of statistical tests to determine whether site-specific codon bias in human immunoglobulin genes is correlated with the sequence specificity of the somatic mutation mechanism. The sequence specificity of the mutator was determined by analysis of a database of published immunoglobulin intron sequences that had experienced somatic mutation but not selection. The site-specific codon bias was determined by analysis of published sequences of human germline immunoglobulin V genes. Both tests strongly suggest that evolution has acted to enhance the plasticity of immunoglobulin genes under somatic hypermutation.

Amino Acids↗
PubMed1997

Midline teratomas, mullerianosis, the multifariousness of gynaecological neoplasias, and the scrotum. Are they manifestations of a germ-soma barrier?

Empirical evidence and theoretical considerations suggest that there are mechanisms protecting the germ line from untoward somatic influences. In the intraorganismal competition between cell lineages, evolution will give priority for protection to the germ line, which carriers the heritable genes. In embryogenesis, germ cells migrate along the midline as this is an area where developmental influences are lower; exposure to somatic factors may cause inception of teratomas. In order not to hinder the germ line, the female genital tract has a reduced level of cell determination, which results in the multifariousness of gynaecological proliferations, including mullerianosis. The external location of testes reduces somatic constraints on spermatogenesis.

Adult↗
PubMed1994

Evidence that the clonogenic cell in multiple myeloma originates from a pre-switched but somatically mutated B cell.

There is still much controversy about the precursor cell type in multiple myeloma (MM). Some authors claim that it is a pre-B cell, others state that it is a memory B cell or plasmablast. We have recently shown that the VDJ region of the MM immunoglobulin heavy chain gene is somatically hypermutated and antigen selected, without intraclonal variation or evolution in time. By using a patient-specific PCR approach we have now obtained evidence that the premyeloma cell can be situated in the pre-switched B-cell compartment and that heavy chain switching can occur without further somatic mutation. Based on the MM immunoglobulin sequences derived from the bone marrow, patient-specific CDR2 and CDR3 oligonucleotides were designed. B lymphocytes were separated from plasma cells based on the expression of CD19 and HLA class II or surface bound IgM using immunomagnetic beads. The expressed Ig sequences were amplified by RT-PCR using patient specific CDR2 primers and isotype specific primers (C mu, C gamma, and C alpha). Myeloma-specific Ig sequences were detected by a myeloma-specific CDR3 probe and sequenced. In one out of five cases we found in the peripheral blood clonally related IgM and IgA sequences with the same somatic mutations as the MM-IgG sequence. In another case of an IgG MM we found in the bone marrow clonally related IgA sequences with the same somatic mutations. These findings, together with the fact that myeloma-Ig genes contain somatic mutations without intraclonal variation, suggest that the clonogenic cell in multiple myeloma can originate from a pre-switched but somatically mutated B cell.

Amino Acid Sequence↗
PubMedDate not supplied

Network theory of aging.

Evolution theory indicates that investment in mechanisms of somatic maintenance and repair is likely to be limited, suggesting that aging may result from the accumulation of unrepaired somatic defects. An important corollary of this hypothesis is that multiple mechanisms of aging operate in parallel. We describe a recently developed "network theory of aging" that integrates the contributions of defective mitochondria, aberrant proteins, and free radicals in the aging process and that includes the protective effects of antioxidant enzymes and proteolytic scavengers. Possibilities for further extension of the theory and its role in prediction and simulation of experimental results are discussed.

Aging↗
PubMed1998

Molecular evolution of a sex determination protein. FEM-2 (pp2c) in Caenorhabditis.

Somatic sex determination in Caenorhabditis elegans involves a signal transduction pathway linking a membrane receptor to a transcription factor. The fem-2 gene is central to this pathway, producing a protein phosphatase (FEM-2) of the type 2C (PP2C). FEM-2 contains a long amino terminus that is absent in canonical PP2C enzymes. The function of this domain is difficult to predict, since it shows no sequence similarity to any other known proteins or motifs. Here we report the cloning of the fem-2 homologue from Caenorhabditis briggsae (Cb-fem-2). The sequence identity is much higher than that observed for other C. briggsae homologues of C. elegans sex determination proteins. However, this level is not uniform across the entire lengths of the proteins; it is much lower in the amino termini. Thus, the two domains of the same protein are evolving at different rates, suggesting that they have different functional constraints. Consistent with this, Cb-FEM-2 is able to replace some, but not all, of the Ce-FEM-2 in vivo function. We show that removal of the amino terminus from Ce-FEM-2 has no effect on its in vitro phosphatase activity, or its ability to replace the in vivo function of a yeast PP2C enzyme, but that it is necessary for proper FEM-2 function in worms. This demonstrates that the amino terminus is not an extended catalytic domain or a direct negative regulator of phosphatase activity.

Amino Acid Sequence↗
PubMed1986

Population consequences of mutagenesis and antimutagenesis.

Although the progress in basic understanding of mutagenesis and in techniques for precise measurement of mutation rates in test systems has been enormous, there has been very little progress in applying this information to estimates of germline mutation in humans, and even less in translating such estimates into quantitative assessments of the impact on future generations. This doesn't mean that new information about the mutation process, and antimutagens in particular, is not useful. Lowering the human mutation rate would be good, even if we can't say how good. Some simple population kinetics of a change of mutation are discussed, and it is shown that future environmental changes can be ignored if we assume that the impact of a disease on human welfare is changed by the environment in the same proportion as its effect on fitness. Since the human mutation rate appears to be much higher in males than in females, it would be especially important to find ways of reducing the male rate. The role of transposable elements in determining human spontaneous mutation rates is unknown, but unless data from experimental organisms are grossly misleading, this role may be substantial. It is sometimes argued that such responses as error-prone repair systems may be an evolutionary strategy to allow the population to try a larger repertoire of mutations in times of environmental change. They may also be a survival strategy. I suggest that, although such an evolutionary strategy may possibly be adopted in asexual organisms with a very high reproductive rate, it is very unlikely in Mendelian species with limited reproduction such as most higher animals. The amount of existing variability in a large population is so great relative to that which arises in a few generations by mutation that segregation and recombination of existing alleles would appear to be a better way of coping with changing environment. As the human age of reproduction has increased in the recent evolutionary past, it is possible that the compensatory adjustment of mutation rates has not been fast enough to keep up. Perhaps evolution of mutation rates is more determined by selection to reduce somatic mutation than by selection to reduce germinal mutation. Regardless of the answer to the question of the optimum mutation rate for long-time evolution, in my view, the optimum mutation rate from the standpoint of human welfare for the foreseeable future is zero.

Animals↗
PubMed1984

[Genetic bases of antibody diversity].

Repertoire of immunoglobulin paratopes is estimated as at least 10(7)-10(8) per individual. This repertoire is created by the variability of paratope coding VH- and VL-genes. Three events contribute to the necessary diversity of VH- and VL-genes: 1. Sets of germline DNA segments: VH, DH, JH and VL, JL containing genetic information for different parts of V-domains amino acid sequence. 2. Ontogenic rearrangements of these segments resulting in generation and expression of complete VH- and VL-genes. These rearrangements create the third hypervariable region diversity. 3. Succeeding hypermutational process leading to numerous substitutions of single amino acids along the V-domain localized essentially in hypervariable (complementary determining) regions. This process possesses the greatest possibilities for generation of somatic diversity of V-genes. Final VH- and VL-genes diversity reaches the necessary paratope repertoire, due to epigenetic mechanism of heavy and light chains combination in immunoglobulin molecules. Mechanisms of somatic generation of V-genes diversity are interpreted to spring up and be maintained in the course of evolution because of the fact that micro-parasites (viruses and bacteria) have much higher changeability rate than their hosts--highest vertebrates. Since future evolution of micro-parasites cannot be foreseen with the past events as a basis, natural selection of many thousands of germline V-genes fails to bring adaptation of the immune system to changeability of infection agents. Optimal evolution strategy of immunoglobulin gene complex of host species is expected to ensure developing somatic mechanisms. These mechanisms would generate de novo broad and random V-gene variability which is able, through structure diversity of corresponding paratopes, to foresee not only arbitrary micro-parasite, but also any arbitrary antigen not known in phylogenesis.

Animals↗
PubMed1993

Developmental differences in methylation of human Alu repeats.

Alu repeats are especially rich in CpG dinucleotides, the principal target sites for DNA methylation in eukaryotes. The methylation state of Alus in different human tissues is investigated by simple, direct genomic blot analysis exploiting recent theoretical and practical advances concerning Alu sequence evolution. Whereas Alus are almost completely methylated in somatic tissues such as spleen, they are hypomethylated in the male germ line and tissues which depend on the differential expression of the paternal genome complement for development. In particular, we have identified a subset enriched in young Alus whose CpGs appear to be almost completely unmethylated in sperm DNA. The existence of this subset potentially explains the conservation of CpG dinucleotides in active Alu source genes. These profound, sequence-specific developmental changes in the methylation state of Alu repeats suggest a function for Alu sequences at the DNA level, such as a role in genomic imprinting.

5-Methylcytosine↗
PubMed1996

The immune system: a look from a distance.

The self-nonself discrimination is germline encoded for defense mechanisms, but it is somatically learned for the immune system and this is the fundamental difference between the two. When referring to the defense mechanisms of vertebrates, immunologists like to use the term "innate immune systems" to describe the germline encoded class of defense mechanism. It was the acquisition of a somatically learned S-NS discrimination during vertebrate evolution that permitted the immune system to develop large recognitive repertoires compared to those of defense mechanisms. This seemingly boundless immune repertoire has fascinated immunologists for almost a century. Today we have a better understanding of the size and function of the antibody repertoire. Humoral antibody effector functions depend upon secreted immunoglobulin and the concentration of antibody must reach a minimum effective threshold in a short enough time to stop a growing pathogen before it becomes lethal. This requires that initially an equivalent number of B-cells per ml respond to the pathogen. This number of B-cells must respond for each and every milliliter of animal. Consequently, the humoral immune system must be iterated. This straightforward conclusion has far reaching implications, some of which are explored in this review.

Animals↗