The dual role of Spn-E in supporting heterotypic ping-pong piRNA amplification in silkworms

The PIWI-interacting RNA (piRNA) pathway plays a crucial role in silencing transposons in the germline. piRNA-guided target cleavage by PIWI proteins triggers biogenesis of new piRNAs from the cleaved RNA fragments. This process, known as the ping-pong cycle, occurs between two PIWI proteins, Siwi and BmAgo3, in silkworms. Spindle-E (Spn-E), a putative ATP-dependent RNA helicase, is essential for piRNA production in flies and silkworms. However, the specific role of Spn-E in piRNA biogenesis remains unclear. Here, we show that Spn-E is necessary for BmAgo3-dependent production of Siwi-bound piRNAs in the ping-pong cycle and that this function of Spn-E requires its ATPase activity. At the same time, Spn-E acts to suppress homotypic Siwi-Siwi ping-pong, but this function of Spn-E is independent of its ATPase activity. These results highlight the dual role of Spn-E in facilitating proper heterotypic ping-pong in silkworms.