WA telomere is a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos (τέλος) "end" and merοs "part". For vertebrates, the sequence of nucleotides in telomeres is 5′-TTAGGG-3′, with the complementary DNA strand being 3′-AATCCC-5′, with a single-stranded TTAGGG overhang. This sequence of TTAGGG is repeated approximately 2,500 times in humans. In humans, average telomere length declines from about 11 kilobases at birth to fewer than 4 kilobases in old age, with the average rate of decline being greater in men than in women.
WAstragalus propinquus (syn. Astragalus membranaceus, commonly known as Mongolian milkvetch in English and as huáng qí, běi qí or huáng huā huáng qí, in Chinese, is a flowering plant in the family Fabaceae. It is one of the 50 fundamental herbs used in traditional Chinese medicine. It is a perennial plant and it is not listed as being threatened.
WCajal bodies (CBs) also coiled bodies, are spherical nuclear bodies of 0.3–1.0 µm in diameter found in the nucleus of proliferative cells like embryonic cells and tumor cells, or metabolically active cells like neurons. CBs are membrane-less organelles and largely consist of proteins and RNA. They were first reported by Santiago Ramón y Cajal in 1903, who called them nucleolar accessory bodies due to their association with the nucleoli in neuronal cells. They were rediscovered with the use of the electron microscope (EM) and named coiled bodies, according to their appearance as coiled threads on EM images, and later renamed after their discoverer. Research on CBs was accelerated after discovery and cloning of the marker protein p80/Coilin. CBs have been implicated in RNA-related metabolic processes such as the biogenesis, maturation and recycling of snRNPs, histone mRNA processing and telomere maintenance. CBs assemble RNA which is used by telomerase to add nucleotides to the ends of telomeres.
WCell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division; a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis), and a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis). In cell biology, mitosis (/maɪˈtoʊsɪs/) is a part of the cell cycle, in which, replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained. In general, mitosis is preceded by the S stage of interphase and is often followed by telophase and cytokinesis; which divides the cytoplasm, organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. The different stages of Mitosis all together define the mitotic (M) phase of an animal cell cycle—the division of the mother cell into two daughter cells genetically identical to each other. Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, and sister chromatids are separated in the second division. Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor.
WCerebroretinal microangiopathy with calcifications and cysts (CRMCC) is a rare genetic disorder, which affects multiple organs. Its hallmarks are widespread progressive calcifications, cysts and abnormalities of the white matter of the brain, usually occurring together with abnormalities of the blood vessels of the retina. Additional features include poor prenatal growth, preterm birth, anemia, osteopenia and bone fractures, and gastrointestinal bleeding. It is caused by compound heterozygous mutations in the conserved telomere maintenance component 1 (CTC1) gene, but its exact pathophysiology is still not well understood.
WA chromatid is one half of a duplicated chromosome.
WChromatin bridge is a mitotic occurrence that forms when telomeres of sister chromatids fuse together and fail to completely segregate into their respective daughter cells. Because this event is most prevalent during anaphase, the term anaphase bridge is often used as a substitute. After the formation of individual daughter cells, the DNA bridge connecting homologous chromosomes remains fixed. As the daughter cells exit mitosis and re-enter interphase, the chromatin bridge becomes known as an interphase bridge. These phenomena are usually visualized using the laboratory techniques of staining and fluorescence microscopy.
WConstitutive heterochromatin domains are regions of DNA found throughout the chromosomes of eukaryotes. The majority of constitutive heterochromatin is found at the pericentromeric regions of chromosomes, but is also found at the telomeres and throughout the chromosomes. In humans there is significantly more constitutive heterochromatin found on chromosomes 1, 9, 16, 19 and Y. Constitutive heterochromatin is composed mainly of high copy number tandem repeats known as satellite repeats, minisatellite and microsatellite repeats, and transposon repeats. In humans these regions account for about 200Mb or 6.5% of the total human genome, but their repeat composition makes them difficult to sequence, so only small regions have been sequenced.
WDyskeratosis congenita (DKC),also known as Zinsser-Engman-Cole syndrome, is a rare progressive congenital disorder with a highly variable phenotype. The entity was classically defined by the triad of abnormal skin pigmentation, nail dystrophy, and leukoplakia of the oral mucosa, but these components do not always occur. DKC is characterized by short telomeres. Some of the manifestations resemble premature ageing. The disease initially mainly affects the skin, but a major consequence is progressive bone marrow failure which occurs in over 80%, causing early mortality.
WHomeobox containing 1, also known as homeobox telomere-binding protein 1 (HOT1), is a protein that in humans is encoded by the HMBOX1 gene. HMBOX1 directly binds to the double-stranded repeat sequence of telomeres.
WHomologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids. It is widely used by cells to accurately repair harmful breaks that occur on both strands of DNA, known as double-strand breaks (DSB), in a process called homologous recombinational repair (HRR). Homologous recombination also produces new combinations of DNA sequences during meiosis, the process by which eukaryotes make gamete cells, like sperm and egg cells in animals. These new combinations of DNA represent genetic variation in offspring, which in turn enables populations to adapt during the course of evolution. Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses.
WIn molecular biology, the kinase binding protein CGI-121 family of proteins includes the kinase binding protein CGI-121 and its homologues. CGI-121 has been shown to bind to the p53-related protein kinase (PRPK). CGI-121 is part of a conserved protein complex, KEOPS. The KEOPS complex is involved in telomere uncapping and telomere elongation. This family of proteins also include archaeal homologues.
WA mega-telomere, is an extremely long telomere sequence that sits on the end of chromosomes and prevents the loss of genetic information during cell replication. Like regular telomeres, mega-telomeres are made of a repetitive sequence of DNA and associated proteins, and are located on the ends of chromosomes. However, mega-telomeres are substantially longer than regular telomeres, ranging in size from 50 kilobases to several megabases.
WNon-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as "non-homologous" because the break ends are directly ligated without the need for a homologous template, in contrast to homology directed repair, which requires a homologous sequence to guide repair. The term "non-homologous end joining" was coined in 1996 by Moore and Haber.
WA reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by certain viruses such as HIV and the hepatitis B virus to replicate their genomes, by retrotransposon mobile genetic elements to proliferate within the host genome, and by eukaryotic cells to extend the telomeres at the ends of their linear chromosomes. Contrary to a widely held belief, the process does not violate the flows of genetic information as described by the classical central dogma, as transfers of information from RNA to DNA are explicitly held possible.
WPlasmodium falciparum is a unicellular protozoan parasite of humans, and the deadliest species of Plasmodium that causes malaria in humans. The parasite is transmitted through the bite of a female Anopheles mosquito and causes the disease's most dangerous form, falciparum malaria. It is responsible for around 50% of all malaria cases. P. falciparum is therefore regarded as the deadliest parasite in humans, causing 405,000 deaths in 2018. It is also associated with the development of blood cancer and is classified as Group 2A carcinogen.
WTelomestatin is a macrocyclic chemical compound that acts by inhibiting the telomerase activity of in vitro cancer cells. It was first isolated from the bacteria Streptomyces anulatus. Telomestatin induces the formation of basket-type G-quadruplex (G4) structures from hybrid-type G-quadruplexes in the telomeric region. Upon formation of G4 structure there will be a decrease in the activity of the telomerase, which is involved in the replication of the telomeres and as a result the cell dies due to Hayflick type senescence.
WZinc finger and BTB domain containing 48 (ZBTB48), also known as telomeric zinc-finger associated protein (TZAP), is a protein that directly binds to the double-stranded repeat sequence of telomeres. In humans it is encoded by the ZBTB48 gene.