Telomere regulation and function during meiosis Biology Diagrams Telomeres are the physical ends of eukaryotic chromosomes. They protect chromosome ends from DNA degradation, recombination, and DNA end fusions, and they are important for nuclear architecture. Telomeres provide a mechanism for their replication by semiconservative DNA replication and length maintenance by telomerase. 1. Telomere structure and maintenance 1) Telomeric DNA and G-quadruplex. Telomeres are comprised of repeat sequences and bound by multiple telomeric interacting proteins. In mammalian cells, telomere DNA contains double-stranded tandem repeats of TTAGGG followed by terminal 3โฒ G-rich single-stranded overhangs.
Given that nuclear DNA cannot be fully replicated during mitosis (i.e. end replication problem), telomeres shorten with each round of cell division, unless acted upon by different telomere The maintenance of telomere length is a prerequisite for the continuous division of cells, so telomerase is more active in cells that need to sustain division, such as tumor cells, stem cells, etc. And telomerase is specifically designed as a reverse transcriptase to resist telomere shortening. Together these data indicate that aged C19orf43-depleted cells exhibit cohered telomeres in mitosis that are held together by RNA-DNA hybrids and are protected from DNA damage and senescence. RNaseH1 regulates TERRA-telomeric DNA hybrids and telomere maintenance in ALT tumour cells. Nat. Commun 5, 5220. 10.1038/ncomms6220. [PMC free article
loops connect and protect sister telomeres in mitosis Biology Diagrams
Dyskerin is a highly conserved, nucleolar RNA-binding protein with established roles in small nuclear ribonucleoprotein biogenesis, telomerase and telomere maintenance and precursor rRNA processing. Telomerase is functional during S phase and the bulk of rRNA maturation occurs during G 1 and S phases; both processes are inactivated during mitosis. MUS81 operates in distinct phases of the cell cycle, during S phase, MUS81 forms a complex with EME2, crucial for fork cleavage and telomere maintenance in cells dependent on the alternative Mammalian telomeres are composed of TTAGGG repeats bound by a six-protein complex called shelterin. The G-rich 3โฒ terminating strand forms a ssDNA overhang that is also necessary for telomere maintenance because it can invade into the double-stranded telomeric DNA to form a protective structure called the t-loop [64,65].