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Chromosome Y does not recombine with any other at meiosis except that on pseudoautosomal region. Polymorphic markers on the chromosome Y are paternal inheritance and are haploidly inherited. Variance of the sequences comes from accumulated mutation. These properties make them unique and important not only to anthroponomy and genetics but also to forensic science and medicine.
Pancreatic ductal carcinoma remains the 4th leading cause of cancer death in both men and women in the United States, with an overall 5-year survival of less than 3%. Over the last decade, significant advances have been made in our understanding of the molecular biology of pancreatic ductal carcinoma, with pancreatic cancer now considered one of the better characterized neoplasms at the genetic level. The advances in the understanding of the molecular genetics of pancreatic cancer initially focused on events that occur in the development and early genetic progression of the disease. This progression has been associated with the accumulation of multiple genetic alterations in various cancer-causing genes, leading to the development of a histological and genetic progression model. In the model, pancreatic cancer develops from non-invasive intraepithelial precursor lesions termed pancreatic intraepithelial neoplasias, with each progressive stage associated with accumulated mutations in oncogenes, tumor-suppressor genes, and mismatch repair genes. Other aspects of the development of pancreatic ductal carcinoma, such as tumor invasion, tumor-stromal interaction, metastasis, and chemotherapeutic resistance are more poorly understood. Recent studies utilizing global gene expression methodologies have provided insight into some of these processes and have allowed for the development of potential tumor markers which could be used for early detection and diagnosis of this difficult disease. In order to improve the survival of patients with pancreatic carcinoma, we need to better understand the fundamental changes that occur in pancreatic ductal carcinoma. The following article reviews the genetic mutations and syndromes known to be associated with pancreatic ductal carcinoma as well as recent advances in the study of global gene expression.
In this mini review, we present assumptions and some results of Monte Carlo simulations based on the Penna model, which support the mutation accumulation theory of aging. This microscopic model has been exploited for the quantitative description of many biological phenomena connected with the population evolution. We show how the results of simulations could describe the changes of mortality trajectories of the human populations during the last 150 years, and how the method could be used for predicting the human age distribution in the future. The main assumption of the model is that genes are expressed chronologically one after another in the same order in all individuals during their life span. Different forces of selection pressure exerted on genes expressed at different periods of life generate characteristic gradient of defective genes accumulated in the germline cells. The genes expressed after the minimum reproduction age are under weaker selection pressure, and the fraction of defects among them is higher than among the genes expressed before the minimum reproduction age. This gradient of defects generates a gradient of mortality for the part of the population in the reproduction age following the exponential Gompertz law. The limitations of the model and some biological interpretations of its parameters are also discussed.
The blood-related cancer leukemia was the first disease where human cancer stem cells (CSCs), or leukemic stem cells (LSCs), were isolated. The hematopoietic system is one of the best tissues for investigating cancer stem cells, since the developmental hierarchy of normal blood formation is well defined. Leukemia can now be viewed as aberrant hematopoietic processes initiated by rare leukemic stem cells (LSC) that have maintained or reacquired the capacity for indefinite proliferation through accumulated mutations and/or epigenetic changes. Yet, despite their critical importance, much remains to be learned about the developmental origin of LSC and the mechanisms responsible for their emergence in the course of the disease. This report will review our current knowledge on leukemic stem cell development and finally demonstrate how these discoveries provide a paradigm for identification of Cancer Stem Cell (CSC) from solid tumors.
mtDNA has been widely used as a molecular marker to investigate the phylogenesis of many species. D-Loop has important value for investigating intraspecific genetic differentiation because of its high mutation accumulation. Fish is the most primitive vertebrate, but by far is the most dominant in number. The distribution of fish is broad and its origin is very complicated, has always been a very interesting subject for investigation. D-Loop has many important implications for investigating the intraspecific genetic differentiation of fish. Recently, much insight has been gained by the increasing use of D-Loop as a molecular marker for investigating the intraspecific genetic differentiation of fish. Lake Qinghai is the biggest inland saline lake in China. The main fish in the lake is scaleless carp (Gymnocypris przewalskii). Initial analysis of its D-Loop showed no intraspecific genetic differentiation among the populations in the lake and the rivers around.
Mildly deleterious mutations are thought to play a major role in the extinction of natural populations, especially those that are small, isolated, or inbred. Self-fertilization should reduce the effective size of populations and simultaneously reduce migration between populations. A history of self-fertilization should therefore cause a population to harbor a substantial "local drift load" caused by the fixation of mildly deleterious mutations. This hypothesis was tested in Leavenworthia alabamica, which contains large, self-incompatible populations and smaller self-compatible populations with adaptations for self-fertilization. The fitness of offspring from within- and between-population crosses was compared to quantify heterosis caused by the masking of deleterious alleles in the heterozygous state. Little heterosis was observed in crosses between five large, self-incompatible populations and two of the three small, self-fertilizing populations of L. alabamica. However, the most geographically isolated and genetically divergent self-fertilizing population (Tuscumbia) exhibited a 110.2% increase in germination and a 73.6% increase in fitness, which is consistent with a sizeable local drift load. The finding of substantial heterosis for fitness supports the idea that small effective size, reproductive isolation, and self-fertilization can make populations particularly vulnerable to mutation accumulation.
With respect to the recent discoveries related to activation and effects of oncogenes, it should be postulated that malignant transformation is due to their inappropriate activation. The postulate must be taken into account when analyzing any other question concerning malignant tumors, e.g. the role of genetic and environmental factors, defence mechanisms, strategy of prevention and treatment, etc. It is argued in this paper that a) in principle, tumors are caused by the events occurring within the body (oxidative radicals that damage DNA), whereas the environmental factors influence the incidence of certain tumors only superficially, eliciting no effect upon the overall tumor incidence; b) malignant transformation (tumors) is one of the consequences of biological deterioration of the body which, like aging, is caused by mutation accumulation; the death due to a malignant tumor is "one of the mechanisms of dying due to the aging process", c) congenital resistance to tumors mostly concerns the quality of DNA, less the influence of classical defence mechanisms, like immune system; d) malignant tumors are relatively more frequent today, which should not be ascribed to (increased) environmental pollution but is due to the increased longevity of contemporary man, and possibly to negative selection materialized through extremely effective modern medicine. Future research will bring about detailed understanding of the mechanisms of action and interaction of oncogenes in the process of cell malignant transformation for numerous types of tumors, elucidation of the role of oncogenic viruses and, much later, use of drugs providing protection against oncogenic viruses and selectively killing the transformed cells, at least in some (early) phases of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)
There are two different views on the evolution of life forms in Cormophyta: from woody plants to herbaceous ones or in opposite direction - from herbs to trees. In accordance with these views it is supposed that life span in plants changed in the course of evolution from many years (perennials) to few years (annuals, biennials), or went in reverse - from few years to many years. The author discusses the problems of senescence and longevity in Cormophyta in the context of various hypotheses of ageing (programmed death theory, mutation accumulation, antagonistic pleiotropy, disposable soma, genes of ageing, genes of longevity). Special attention is given to bio-morphological aspects of longevity and cases of non-ageing plants ("negative senescence", "potential immortality"). It is proposed to distinguish seven models of simple ontogenesis in Cormophyta that can exemplify the diversity of mechanisms of ageing and longevity. The evolution of life span in plants is considered as an indirect result of natural selection of other characteristics of organisms or as a consequence of fixation of modifications (episelectional evolution). It seems that short life span could emerge several times during evolution of one group of plants, thus favoring its adaptive radiation.
Asexual reproduction is thought to doom organisms to extinction due to mutation accumulation and parasite exploitation. Theoretical models suggest that parthenogens may escape the negative effects of conspecifics and biological enemies through escape in space. Through intensive sequencing of a mitochondrial DNA (mtDNA) and a nuclear intron locus in sexual and parthenogenetic freshwater snails (Campeloma), I examine three questions: (1) Are sexual mtDNA lineages more restricted geographically than parthenogenetic mtDNA lineages? (2) Are independent parthenogenetic lineages shorter lived than sexual lineages? and (3) Do parthenogens have higher intraindividual nuclear sequence diversity and form well-differentiated monophyletic groups as expected under the Meselson effect? Geographic ranges of parthenogenetic lineages are significantly larger than geographic ranges of sexual lineages. Based on coalescence times under different demographic assumptions, asexual lineages are short lived, but there is variation in clonal ages. Although alternative explanations exist, these results suggest that asexual lineages may persist in the short term through dispersal, and that various constraints may cause geographic restriction of sexual lineages. Both allotriploid and diploid Campeloma parthenogens have significantly higher allelic divergence within individuals, but show limited nuclear sequence divergence from sexual ancestors. In contrast to previous allozyme evidence for nonhybrid origins of diploid Campeloma parthenogens, cryptic hybridization may account for elevated heterozygosity.
Retroviruses-derived elements in the human genome constitute 90% of non-coding mobile sequences. Reverse transcriptase (RT) plays an essential role in their transposition as do long terminal repeats (LTRs), which contain promotors, enhancers, and regulatory sequences. Some retroelements (pseudogens and retrogenes, e.g. SINE) are non-autonomic and do not possess their own RT. These elements are dependent on autonomic elements (retroposons, e.g. LINE, retrotransposons, exo- and endogenous retroviruses). The genome of retroviruses is composed of gag, pol, and env genes flanked by long terminal repeats. Endogenous retroviruses are probably the remnants of ancient germ cell infection by exogenous retroviruses and are transmissible to the next generation in a Mendelian way. Most of them are defective (because of mutation accumulation), but some are still active and their expression is regulated by different factors (UV radiation, inflammatory cytokines, steroid hormones, and exogenous virus products). Retroelements as well as their gene products exert influence on the organism's functions. They influence the plasticity and evolution of genomes, are a source of promotors and regulatory sequences, but they also supply additional signals of transcription initiation, mRNA splicing, and STOP codons. One of the positive aspects of human endogenous retroviruses (HERVs) is the participation of their products in normal syncytiotrophoblast formation. They also block exogenous retrovirus replication by receptor interference or antisense mRNA. Their presence is considered to be connected with a number of autoimmunological diseases (multiple sclerosis, insulin-dependent diabetes mellitus, systemic lupus erythematosus), cancer, or even psychiatric disorders (schizophrenia). There are also other problems connected with the potential role of ERVs in genomic therapy (with retroviruses vectors) and transplantology (xenotransplantation).
Evidence has accumulated that quiescent stem cells or cells developmentally closely related to them distributed in various organs may be a cellular origin of cancer development. In support of this notion, stem cells (SC) are long-lived cells with distinctive properties of self-renewal and has the potential to proliferate extensively. Given these features, it's possible that they may become the subject of consecutive accumulated mutations that are crucial for initiation of cancer. Therefore, mutations that occur in normal stem cells might lead to their malignant transformation and tumor initiation. Furthermore, many biological features of normal and cancer SC such as the physiological trafficking of normal and metastasis of cancer stem cells involve similar molecular mechanisms, and we discuss these similarities here.
A 1468 b.p. DNA BamHI-fragment homologous to the Bsp-repeat was isolated from the fox genome and sequenced. This fragment is an hierarchically arranged dimer. Its 734 b.p.-monomers consist of three subrepeats (SR), each 245 b.p. long, abundant with overlapping imperfect tandem repeats which in turn are rich in short direct related repeats (each 4-7 b.p. in size). The latters are mainly composed of AG, TG dinucleotides and their complements CT, CA. All subrepeats in the BamHI-dimer are flanked by motifs homologous to Jeffreys' sites. At certain points the sites are doubled. The above data allow to assume that the Bsp-repeat complex structure is likely to have developed throughout long multi-step evolution of relatively simple DNA sequences which had emerged de novo. Single substitutions, small inserts and deletions, multiple duplication and recombination events seem to have most contributed to the evolution of the Bsp-repeats. Single substitutions in SRs with respect to the consensus are not equally distributed along their length. A wave-like pattern of this distribution is the evidence for non-random character of mutations accumulation. A correspondence was noted between conservative regions in SR and the presence therein of functional motifs homologous to the binding sites of already known regulatory proteins.
We demonstrated that nucleotide and amino acid sequences in the carboxyl-terminal regions of rat, mouse, and human prepropancreatic polypeptide exhibit a high degree of divergence, whereas the amino-terminal domains are highly conserved. To understand the molecular basis of this divergence and conservation, we determined the nucleotide sequence of the rat pancreatic polypeptide gene from an islet genomic library and compared it with that of the human gene. Exon 2 of the rat gene encodes the signal peptide and pancreatic polypeptide, exon 3 encodes the carboxyl-terminal region, and exons 1 and 4 encode the 5'- and 3'- untranslated regions of the mRNA, respectively. Exons 1 and 2 of rat and human genes are well conserved. The rat and human genes, however, have exons 3 and 4 of different lengths and heterologous nucleotide sequences. Mutational accumulation in exons 3 and 4 and intron 3 of the rat gene appears to have caused splice junction sliding and translational frameshift, resulting in a structural divergence in the carboxyl-terminal region. Available evidence indicates that the mosaicism of structural conservation and divergence in pancreatic polypeptide genes may have been caused by a difference in the evolutionary rates of the genomic regions.
Many areas of research are contributing to our understanding of WT and the role of WT1 in development of the renal and genitourinary systems. Characterization of putative target genes and the control of their expression continues. The importance of isoform ratios and imprinting effects are also under active investigation, often using animal models. The accumulating mutation data, together with evolutionary studies, illuminate WT1 structure-function relationships, highlighting the regions critical in normal development and tumorigenesis. And last, but by no means least, the hunt for the WT2 and WT3 genes continues.
It has been suggested that mutations accumulated in mitochondrial DNA during the aging process may be causally related to the decreased physiological response of the senescent organisms. We have quantified and evaluated the integrity of the mitochondrial genome during the life span of Drosophila melanogaster. Its amount remains fairly constant representing roughly 1% of the total DNA at all ages. Southern experiments have also revealed a high stability and integrity of the mitochondrial DNA (mtDNA). However, we have detected an important decrease in the steady-state levels of all mitochondrial transcripts investigated: 16 S ribosomal RNA (16SrRNA), cytochrome c oxidase, cytochrome b, and beta H(+)-ATP synthase subunit. These changes correlate with the shape of the life span curve, preceding the decrease in survival of the male flies used in the study, and at least in the case of 16SrRNA, is tissue-specific. Although mitochondrial DNA remains unchanged in heads, thoraces, and abdomens, 16SrRNA levels decrease more severely in heads and thoraces and much less conspicuously in abdomens. On the other hand, control non-mitochondrial transcripts investigated remain essentially unaffected. These results suggest that in Drosophila the main effect of aging on the mitochondrial genetic system is downstream from mtDNA itself. The decline in the levels of beta H(+)-ATPase transcript, nuclear-encoded, suggests that not only the mitochondrial machinery, but also the nuclear one involved in mitochondrial biogenesis, is affected during aging.
Nucleotide excision repair is a versatile process and is one of the best known systems that prevents the deleterious consequences of DNA damage induced by environmental agents and cellular metabolites. Without repair, persisting lesions can interfere with proper functioning of DNA-metabolizing processes, notably transcription and replication, and give rise to mutations. The effect of inefficient or deficient repair is illustrated by genetic repair diseases that predispose individuals to cancer due to the fact that mutations accumulate at a high rate. Here we describe the progress that has been made from the initial cloning and characterization of nucleotide excision repair genes to the current understanding of their function in the complex nucleotide excision repair process.
We previously showed that expression of the bovine papillomavirus (BPV) E2 gene results in a dramatic inhibition of the proliferation of several human cervical carcinoma cell lines, including HeLa cells which contain human papillomavirus (HPV) type 18 DNA. We have assessed the status of endogenous G1 cell cycle regulatory proteins, including the tumor suppressor proteins, p53 and p105Rb, in order to investigate growth regulatory pathways in HeLa cells following E2 expression. The p53 tumor suppressor protein is stabilized following the introduction of the E2 gene into HeLa cells. This results in the induction of the p53-responsive gene encoding the cyclin dependent kinase (cdk) inhibitor, p21/WAF1, complex formation between p21/WAF1 and cdk2 and reduction of in vitro cdk2/cyclin E kinase activity. The reduced cdk kinase activity is accompanied by the accumulation of the growth inhibitory hypophosphorylated form of the tumor suppressor protein, p105Rb. The level of the p105Rb-regulated transcription factor, E2F1, is reduced, as is transcription of a variety of E2F1-regulated genes, including B-myb. Thus, the p53 growth inhibitory pathway has evidently not accumulated mutations in HeLa cells but rather appears intact. However, this pathway remains dormant, until it is mobilized by appropriate manipulations, such as the expression of the BPV E2 protein.
It is proposed that genomic integrity is preserved after DNA damage in a variety of ways. X irradiation induces a p53-dependent G1-phase cell cycle checkpoint which putatively allows time for repair of DNA damage. The p53 protein is also involved in the initiation of apoptosis after radiation-induced DNA damage, presumably leading to the elimination of lethally damaged cells from the irradiated population. To test the hypothesis that repair occurs in the additional time provided by the activation of the G1-phase checkpoint, we investigated whether the presence of a G1-phase arrest modified the frequency and type of chromosomal rearrangements at the first mitosis after irradiation. Isogenic cell lines derived from the same human glioma cell line, but differing in p53 status, were used. Purified G1-phase cells, isolated by centrifugal elutriation and X-irradiated, were studied. The wild-type p53 cell line demonstrated a dose-dependent arrest during G1 phase, as determined by flow cytometry. These cells remained in G1-phase as long as 48 h after irradiation. Cells expressing a dominant-negative p53 mutation accumulated to a much lesser extent in G1 phase after irradiation. Cells lacking the G1-phase checkpoint showed increased survival at all radiation doses. There were no significant differences in the type or frequency of total chromosomal aberrations in mitotic cells from either cell line after 1,2,4 or 6 Gy X rays, as measured by conventional cytogenetic analysis. There was an increase, however, in the number of reciprocal translocations in mitotic cells with mutant p53 (lacking a G1-phase checkpoint), as measured by fluorescence in situ hybridization with a chromosome 4-specific DNA library, but only after 6 Gy. The results suggest that the presence of a well-defined p53-dependent G1-phase arrest does not reduce chromosomal aberrations caused by low doses of ionizing radiation markedly, but may reduce the overall degree of survival by triggering other G1-phase events.