Systems-Based Analysis of the Sarcocystis neurona Genome Identifies Pathways That Contribute to a Heteroxenous Life Cycle

Blazejewski, Tomasz; Nursimulu, Nirvana; Pszenny, Viviana; Dangoudoubiyam, Sriveny; Namasivayam, Sivaranjani; Chiasson, Melissa A.; Chessman, Kyle; Tonkin, Michelle; Swapna, Lakshmipuram S.; Hung, Stacy S.; Bridgers, Joshua; Ricklefs, Stacy M.; Boulanger, Martin J.; Dubey, Jitender P.; Porcella, Stephen F.; Kissinger, Jessica C.; Howe, Daniel K.; Grigg, Michael E.; Parkinson, John

The genome analyses identified nine previously reported S. neurona orthologs of T. gondii MICs (MIC7, MIC8, MIC10, MIC12, MIC13, MIC14, MIC15, MIC16, and M2AP) (30) . We also identified potential homologs of MIC2, MIC4, and MIC9 that had not been annotated through the gene model prediction pipeline. MIC4 has previously been shown to form part of a heterocomplex with MIC1 and MIC6 (31) . The absence of the latter two homologs from S. neurona suggests that MIC4 likely mediates the more important functional role. MIC7, MIC8, MIC9, and MIC12 are relatively unique in T. gondii with the possession of epidermal growth factor-like domains, suggesting a potential role in ligand binding. MIC10, together with MIC11 (absent from S. neurona) is thought to be involved in the organization of organellar contents. Also secreted by the microneme is apical membrane antigen 1 (AMA1), which functions to link the inner membrane complex (IMC) to the host cell via interactions with RON proteins that together make up the moving junction (6, 32) . Our searches revealed two loci, separated by approximately 80 kb on the S. neurona assembly's largest scaffold, homologous to T. gondii AMA1 protein TGME49_315730. Interestingly, the reading frames of the two S. neurona paralogs (SnAMA1a and SnAMA1b) occur in opposite directions, suggesting an inverted duplication. Supporting this, two inverted repeats Ͼ100 bp in length and with Ͼ70% identity were identified~20,000 bp apart, separating the two paralogs. While the region upstream of the paralogs appears repeat rich, containing simple repeats, as well as LINEs and DNA elements, the region downstream of the second paralog is uncharacteristically repeat poor, with no repetitive sequences in~14,000 bp of sequence. T. gondii possesses additional paralogs of the AMA1 protein, including TGME49_300130. Again, S. neurona appears to possess these two additional AMA1 paralogs (SnAMA1c and SnAMA1d), but in this case, they are present on two different scaffolds. AMA1 has been shown to interact remarkably strongly with RON2, RON4, and RON5 (32) .