The functional identification of novel genes regulating telomere length in human cells

Telomere length is a highly heritable trait associated with atherosclerotic cardiovascular disease and cancer, therefore identifying and understanding the mechanisms by which genes affect telomere length can have therapeutic benefits. A recent 1000 genomes-based imputation genome wide association study analysis of 46,898 European individuals across 22 cohorts identified genetic variants in 31 loci that associate with human leukocyte telomere length (LTL). Many contain genes known to regulate telomere length, e.g. components of the telomere capping shelterin complex or of the telomerase enzyme required for telomere length maintenance. However, 13 loci cannot be linked to any known telomere regulator, suggesting they may contain genes with previously unidentified roles in telomere biology. The aim of this thesis was to identify these novel genes, investigate how they may regulate telomere biology and uncover the precise pathway through which this is achieved.

Bioinformatics analyses investigated the effects of LTL associated SNPs on gene expression and the amino acid sequence, linking 7 loci with potential candidate genes. A screen was developed which enabled the regulation of telomere maintenance or telomere protection by candidates to be detected. This was achieved through the utilisation of siRNA-induced gene knockdowns and measurement of acute effects on telomerase activity and activation of the DNA damage response, indicative of telomere deprotection. The genes with the strongest evidence linking them to telomere biology – MPHOSPH6, PAPD4, SENP7 and DCAF4 – were selected for screening.

MPHOSPH6 was identified as a promoter of telomerase activity through its involvement in the complex maturation of TERC, the RNA component of telomerase, however the precise mechanism is still to be fully elucidated. Preliminary evidence indicative of the regulation of DNA repair and telomere protection by DCAF4 was also produced, however evidence supporting a link between telomere biology and the activity of PAPD4 and SENP7 was not generated.