Evolution of steroid receptor coactivator Taiman in arthropods.

Insect steroid receptor coactivator TAIMAN (TAI) belongs to the p160/SRC/NCoA family proteins together with the mammalian Steroid/Nuclear Receptor Coactivators 1-3. In the past two decades, TAI has been established as an indispensable key component of both the juvenile hormone (JH) and ecdysone signaling pathways. Although association with the JH and ecdysone pathways has dominated TAI research, several publications have linked insect TAI to additional processes, including Hippo and Hedgehog signaling. To explore TAI diversity, we systematically searched for conserved sequence motifs in TAI proteins across representatives of nearly all insect orders and many non-insect arthropods. Our dataset enabled us to identify new conserved motifs and regions, and to interpret them in the context of insect and arthropod evolution. We demonstrated that the tai gene structure is conserved, with conserved alternative splicing patterns at both the 5' and 3' regions of the gene, and a tendency toward exon fusion in holometabolous species. However, species- and order-specific variations were identified; for example, the C-terminal LxxLL motif was gradually lost in Diptera, resulting in an atypical TAI structure in Drosophila and mosquitoes. Overall, we demonstrated that TAI conservation extends beyond the canonical bHLH and PAS domains. We anticipate that our analyses and the extensive TAI sequence dataset will serve as a comprehensive reference for future TAI research.