Understanding the Relationship between Gender, Estrogen and Telomere Biology in Fish: Towards Developing an Alternative Vertebrate Model for Aging Studies

Telomeres, found at the ends of chromosomes, progressively shorten with age due to inefficiency in DNA replication. Telomeres can be elongated by the telomerase catalytic subunit TERT (TElomerase Reverse Transcriptase).In vitrostudies showed that estrogen activates telomerase activity (TA) through a direct up-regulation of humanTERTtranscription via the estrogen responsive element (ERE). Despite estrogen having been proposed as a key factor contributing to the observed sex difference in telomere lengths (TL) (female > male) and aging in humans, this hypothesis has not been thoroughly tested in mammalian models (i.e. rodents). Telomeres of inbred rodents are extraordinarily long, making it difficult to study the effects of telomere erosion on aging in either short term experiments or within a single generation. Studies using alternative animal models with TL and estrogen biology similar to that of humans are therefore highly desirable to unravel the mechanisms related to sex-dependent regulation of telomere attrition and aging. The small laboratory fish, Japanese medakaOryzia latipes, exhibits gradual senescence, telomere attrition, telomere length,olTERT(gene and protein) sequences homology and estrogen biology which are very similar to that in humans. TheDMYgene identified inO.latipes is the only sex determining gene that has been found in non–mammalian vertebrates thus far, enabling the exact determination of gender in individual fish. Furthermore, the researchers' preliminary studies show gender differences in the TL and TA in the gill ofO. latipes(female > male). The researchers also identified six putative EREs in the promoter region of olTERT gene, and there are six estrogen receptor (olER) isoforms inO. latipes, making it likely that estrogen regulation of TERT transcription is tissue specific.Here it is proposed to useO. latipesas an alternative vertebrate model to study the effects of gender on tissue- and age-dependent changes in TL and associated change in TERT expression and TA. The levels of estrogen will be altered in females (lower) and males (higher) to define the mechanisms of estrogen-mediated regulation of TL through the TERT and TA pathwayin vivo. The involvement of olERs and functional EREs onolTERTgene transcription, and tissue expression of specific olER(s) will be determined to explain tissuespecific telomere regulation inO. latipes. It is hypothesized that estrogen binds to olERs resulting in increased TA through direct upregulation ofolTERTtranscription via ERE(s), leading to longer TLs in femaleO. latipes. Correspondingly, a lower level of estrogen/ERs in male fish may lead to a lower TA and hence shorter TLs.This entirely novel project will (a) unravel the specific role of gender and mechanisms of estrogen in regulating TL in fish; and (b) provide an alternative model for aging research which may overcome the limitations in using the mammalian models. Since the telomere biology and regulation of sex hormones are highly conserved in vertebrates, the results of this study may also unlock the secret of gender (estrogen) on telomere regulation and aging in humans.