Gene expansion and contraction are important evolution events. Some tdrd genes, especially multi-Tudor members, participate in Piwi-interacting RNA pathway and spermatogenesis. However, tdrd evolution and their functions in teleost fish are poorly understood. Here, we identified 14 tdrds in the teleost fish, swamp eel, which were clustered into 12 tdrd branches. Comparative synteny showed biased duplications and loss of members in the tdrd family. Both tdrd6 and tdrd7 were duplicated in the teleost fish, whereas tdrd8 was lost from the original locus. Expression analysis at both RNA and protein levels showed that tdrd6l, a duplicated multi-Tudor member, was gonad enriched. Expression pattern of tdrd6l in follicular epithelium and seminiferous epithelium during sex reversal supports its potential role in genome defense in germline.
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