Identification of POT-3 and its role in telomere length maintenance in Caenorhabditis elegans

Abstract

Telomeres, consisting of repetitive DNA sequences, cap linear chromosomes, to prevent replicative erosion and inappropriate DNA damage responses. Human Protection of Telomeres 1 (POT1) directly interacts with single-stranded telomeric DNA, safeguarding chromosomal ends and contributing to telomere length regulation. In Caenorhabditis elegans, four human POT1 homologs, namely POT-1, POT-2, POT-3, and MRT-1, are present. MRT-1 is essential for telomerase-dependent telomere maintenance and acts as a 3’ to 5’ exonuclease. POT-1 and POT-2 repress telomerase activity and influence telomeric overhang length. However, POT-3 was less well understood. Here, we show that the loss of POT-3 function leads to elongated telomere length and an increased level of circular extrachromosomal telomeric DNA (C-circles). This is consistent with POT-3 behaving as a paralog of POT-2. Interestingly, POT proteins display intricate phenotypic relationships between each other. When quantifying brood size, pot-3 acts epistatically with pot-2 in a POT-1 dependent manner. The extremely long telomeres of pot mutants provided an opportunity to study the inheritance of telomere length in C. elegans. Telomere length inheritance in C. elegans was observed to be a stochastic process, instead of being exclusively parental, with telomeres inherited from both male and hermaphrodite parents, regardless of their length. When worms inherit telomeres of different lengths, long telomeres remain stable while short ones elongate rapidly. Moreover, mrt-1 and trt-1 strains, previously thought to act in the same telomere regulation pathway, display differential responses in fertility span and telomere length shortening to the loss of POT-2 or/and POT-3. These results highlight the complexity of the interplay between these telomeric proteins. This study unveils the role of POT-2 and POT-3 in telomere length and fertility regulation, opening new avenues for future cancer research. Telomere inheritance identification in C. elegans also contributes to the study of telomere inheritance in other organisms.