Putative telomere proteins encoded in the Stylophora pistillata genome
To characterize the structure of coral telomeres, we searched in theS. pistillata host genome (Voolstra et al. 2017) for genes encoding putative shelterin subunits as well as the telomerase catalytic subunit TERT. We identified orthologs of four human shelterin subunits (Rap1, Trf1/2, Pot1, Tpp1 ) and of Tert (Figure 1A-B-C-D-E). The coral genome contains two human Pot1 paralogs, similarly to mouse and Caenorhabditis elegans elegans (Raiceset al. 2008), and only one Trf , in agreement with the duplication of the Trf ancestor in Trf1 and Trf2that occurred at the base of the chordate lineage (Poulet et al.2012) (Figure 1B). The coral Pot1 protein shares a similar structure with the human Pot1, containing two Oligonucleotide/Oligosaccharide-Binding (OB) fold domains located in the N-terminal region and a characteristic split OB fold in the C-terminus (Figure1-G, Supplementary Figure 1). The second ortholog of Pot, named Pot2, contains two OB folds skewed to the C-terminal part of the protein. Therefore, the protein composition of coral telomeres is likely to share many similarities to those of other animals (Figure 1F).