Telomere length and telomerase activity during folliculogenesis in mammals

Abstract

Telomeres are repetitive non-coding DNA sequences located at the ends of chromosomes in eukaryotic cells. Their most important function is to protect chromosome ends from being recognized as DNA damage. They are also implicated in meiosis and synapse formation. The length of telomeres inevitably shortens at the end of each round of DNA replication and, also, as a consequence of the exposure to oxidative stress and/or genotoxic agents. The enzyme telomerase contributes to telomere lengthening. It has been reported that telomerase is exclusively expressed in germ cells, granulosa cells, early embryos, stem cells, and various types of cancerous cells. Granulosa cells undergo many mitotic divisions and either granulosa cells or oocytes are exposed to a variety of genotoxic agents throughout folliculogenesis; thus, telomerase plays an important role in the maintenance of telomere length. In this review article, we have comprehensively evaluated the studies focusing on the regulation of telomerase expression and activity, as well as telomere length, during folliculogenesis from primordial to antral follicles, in several mammalian species including mice, bovines, and humans. Also, the possible relationships between female infertility caused by follicular development defects and alterations in the telomeres and/or telomerase activity are discussed.

Telomere length and telomerase activity in osteoporosis and osteoarthritis (Review)

“…Importantly, the enzyme telomerase can reverse telomere shortening, as it contributes to sustaining TL. However, it exhibits a high activity only in a subgroup of highly proliferating adult somatic cells, e.g., stem and progenitor cells, activated lymphocytes, as well as germline cells (31), while in the majority of adult human somatic cells, the expression and activity of telomerase is undetectable.…”

Telomere length in granulosa cells and leukocytes: a potential marker of female fertility? A systematic review of the literature

“…The development of ovarian follicles requires an acute increase of granulosa cell number from a few cells to tens of thousands before ovulation [38]. Moreover, an insufficient activation of telomerase in early follicular development stages could accelerate telomeric attrition and severely compromise cellular functions necessary for good follicular maturation [38,45,46]. For many years, granulosa has been considered as containing cells with multipotent stem cell characteristics [47], as the possibility of dividing without the need of anchorage [48] and differentiation into varied cell types [49].…”

“…The pattern of this telomerase activity has been studied through the different types of follicle in ovaries and with aging, especially in bovine [52]. It has been found heterogeneous: the highest levels of telomerase activity are found in the smaller rapidly growing preantral follicles [53], followed by a decrease in activity with the maturation of the follicle [45]. This suggests that the high proliferative activity of granulosa cells could be partially linked to telomerase activity [54] and supports the hypothesis that a decrease in this activity may participate in POF.…”

Cellular senescence: Silent operator and therapeutic target in cancer

“…However, telomerase is highly expressed and active in germ cells, stem cells and various types of cancerous tissue to maintain telomere lengths and ensure continuous cell division 11 . Consequently, the use of telomerase inhibitors has emerged as a potential anticancer strategy 12 . The second hypothesis posits that senescence can be induced by oncogenic stimuli and DNA damage.…”