Role of GPCR methuselah and methuselah-like genes in ageing and stemness in Drosophila

Dietary restriction extends lifespan in diverse species. Aside from that inhibition of reproduction is one of the most effective ways to extend animal lifespan. The genetic or surgical ablation of the reproductive system significantly extends lifespan in many animals. In most cases, targeted ablation of germline stem cells significantly extends, and overproliferation shortens the lifespan. However, in some cases ablation of the entire somatic gonad abrogated lifespan extension caused by other factors. Thus, the balance between longevity assurance signals from the somatic gonad and germline affects ageing. At the same time, many interventions with an impact on longevity also affect GSC cell cycle progression in nematodes and fruit flies. Mth is a GPCR associated with longevity. mth1 flies carrying a P-element insertion in the mth locus display lifespan expansion of up to 35%. These animals are resistant to different forms of stress including starvation, temperature and oxidative stress. Nutritional coupling of Mth and its ligand Stunted (Sun) is involved in development and experiments using small-molecule ligands revealed that Mth regulates longevity via the dTOR pathway. In addition, mth1 mutant flies show persistent germline stem cell function with age. However, the molecular relationship between ageing and stem cell maintenance has not been fully unravelled. In this study, I investigated the role of mth and mthl genes in aging and stem cell maintenance. At first, I asked whether ablation of germ cells affects the lifespan of long-lived mth1 mutant animals. These experiments revealed that the complete absence of the germline by mutation of germ cell less (gcl) reduced the lifespan of mth1 mutant animals, whereas killing of adult germ cells in ovaries of mth1 mutant animals by germ line-specific overexpression of Bam increased the lifespan. Overproliferation of GSC-like cells in bam86 ovaries caused lifespan reduction in the mth1 mutant, as did modulation of GSC-like cell overproliferation by UAS-Gal4-mediated bam knockdown in adult female flies. Together, these findings reveal that the effects of germline manipulation and mth-dependent signaling with respect to longevity are additive and thus independent of each other. Previously, studies to uncover stemness factors in GSCs using next-generation sequencing were conducted in our lab. It was found that several mthl genes were differentially expressed in bam86 ovaries, among them mthl7 and mthl8. I have analysed the role of mthl genes in ageing and stem cell maintenance in Drosophila. First, I looked at the expression pattern of mthl genes using modENCODE and other database resources. Interestingly, mthl7 and mthl8 genes were not expressed in ovaries. I tested by fluorescent in situ hybridization whether transcripts of mthl7 and mthl8 were upregulated in bam86 ovaries but that was not the case. Furthermore, germline-specific and somatic knockdown of mthl genes did not impair GSC maintenance, but reduced the lifespan of female flies. Rescue experiments revealed that knockdown of mthl7 and mthl8 in bam86 ovaries did not modify the bam mutant phenotype. Altogether our results indicate that mthl genes are neither involved in GSC maintenance nor in longevity signaling pathways