Telomere stability plays an important role in the preservation of genomic stability and is maintained through the coordinated actions of telomere-specific proteins and DNA repair and replication proteins [1, 2]. Flap endonuclease 1 (FEN1) is a protein that plays a role in lagging-strand DNA replication, base excision repair, homologous recombination, and reinitiation of stalled replication forks [3, 4]. Here, we demonstrate that FEN1 depletion leads to telomere dysfunction characterized by the presence of gammaH2AX and sister telomere loss. Expression of catalytically active telomerase, the reverse transcriptase that adds telomeric repeats to chromosome ends, was sufficient to rescue telomere dysfunction upon FEN1 depletion. Strikingly, FEN1 depletion exclusively abrogates telomeres replicated by lagging-strand DNA replication. Genetic rescue experiments utilizing FEN1 mutant proteins that retained the ability to localize to telomeric repeats revealed that FEN1's nuclease activity and ability to interact with the Werner protein (WRN) and telomere-binding protein (TRF2) were required for FEN1 activity at the telomere. Given FEN1's role in lagging-strand DNA replication and reinitiation of stalled replication forks, we propose that FEN1 contributes to telomere stability by ensuring efficient telomere replication.

Recently, Pacific Biosciences released a new highly accurate long-read sequencer called the Revio System that is projected to generate 30× HiFi whole-genome sequencing for the human genome within one sequencing SMRT Cell. Mouse and human genomes are similar in size. In this study, we sought to test this new sequencer by characterizing the genome and epigenome of the mouse neuronal cell line Neuro-2a. We generated long-read HiFi whole-genome sequencing on three Revio SMRT Cells, achieving a total coverage of 98×, with 30×, 32×, and 36× coverage respectively for each of the three Revio SMRT Cells. We performed several tests on these data including single-nucleotide variant and small insertion detection using GPU-accelerated DeepVariant, structural variant detection with pbsv, methylation detection with pb-CpG-tools, and generatingde novoassemblies with the HiCanu and hifiasm assemblers. Overall, we find consistency across SMRT Cells in coverage, detection of variation, methylation, andde novoassemblies for each of the three SMRT Cells.