Table 1. Expressed placozoan homologs of mouse male germline markers.
| gene name | category | T. adhaerens (H1) accession numbers (JGI-ID) | Placozoa sp. H2 accession numbers | Placozoa sp. H4 accession numbers (EST per cluster) | e-value of best hit against Genbank | e-value of best hit against mouse RefSeq proteins | location in mouse | function in mouse | references |
| sperm associated antigen 8 (spag8) | I | XP_002110904 a | HM243486 | HM243490 (2) | 1e-27 | 2e-07 | sperm acrosome | sperm-oocyte recognition and cell division during spermatogenesis | [30]–[32] |
| Spermatogenesis apoptosis-related protein (dnajb13) | II | XP_002112903 | HM243487 | HM243491 (1) | 1e-113 | 5e-102 | in cytoplasm of spermatids and associated with the axoneme of sperm flagellum | assembly and stability of axoneme during sperm flagellum development and assembly of the annulus structure | [33]–[36] |
| meiosis-specific nuclear structural protein 1 (mns1) | III | XP_002111307 | HM243488 | HM243492 (1) | 8e-122 | 4e-84 | pachytene stage during spermato-genesis | determination and maintenance of the appropriate nuclear morphology during meiotic prophase | [37], [38] |
| meiosis expressed gene 1 (meig1) | III, IV | XP_002109786 | HM243489 | HM243493 (1) | 2e-18 | 7e-17 | spermatocytes when initiating meiosis; | chromatin organization; key in the regulation of spermiogenesis | [39]–[41] |
| non-metastatic cells 5 (nme5) | V | XP_002112439 | n.d. | HM243494 (1) | 2e-69 | 2e-61 | stage 12–16 spermatids | protection of developing male germ cells from beeing killed by oxidastive stress | [42] |
Five homologs of mouse sperm-associated proteins – indicated by high E-values in blast searches – are active in adult, non-degenerating placozoan animals. These proteins were detected after screening EST sequences from Placozoa sp. H4 and subsequently retrieved from the Trichoplax genome (JGI) by blast searches and amplified from a Placozoa sp. H2 cDNA library (see Materials and Methods for details). The putative sperm markers fall within five distinct functional categories: category I = sperm-oocyte recognition; category II = sperm flagellum-associated, category III = male gametocyte meiosis; category IV = control of spermatogenesis; category V = oxidative stress protection. a = EST supported (JGI); n.d. = not detected. For all blast searches the predicted Trichoplax adhaerens protein sequences were used.