DCLRE1B/hSNM1B (Apollo) is not acutely required for human pluripotent stem cell survival

Abstract Telomeric DNA ends in a 3’ single stranded overhang that is implicated in the protective function of telomeres ensuring genomic stability in mammals. Telomere overhang formation relies on the coordinated interplay between DNA synthesis and exonuclease activity. DCLRE1B/hSNM1B/Apollo generates an initial resection at the newly synthesized, blunt-ended leading strand telomere. This resection is thought to be required for further nucleolytic processing at the leading strand telomere. Here, we investigated the functional relevance of Apollo in human pluripotent stem cells (hPSCs) by generating Apollo deficient cells. Leveraging CRISPR/Cas9 technology, we generated locally haploid hPSCs (loHAPs) that lack one allele of Apollo. Subsequently, we mutated the remaining Apollo allele and monitored the resultant allele spectrum over 3 weeks. Surprisingly, cells survived regardless of Apollo status. These results suggest that, in hPSCs, Apollo is not acutely essential for cellular survival.