Silkworm Piwi proteins repressed transcription in an HP1-dependent manner.

(A–F) Transcriptional repression of luciferase 2P (luc2P) reporter gene under the control of the hsp promoter by silkworm Piwi and HP1 proteins in BmN4-SID1 cells with dsRNA against Ago3, Siwi, HP1a or HP1b. The hsp promoter-based luc2P reporter contains five synthetic GAL4-UAS sites and was used in all transfections. BmN4-SID1 cells were transfected with a Luc2P reporter under the control of the hsp promoter, upstream of which five UAS were located for the hsp promoter. Cells were co-transfected with an expression vector for GAL4 DNA-binding domain (DBD)-fused Ago3, Siwi, HP1a or HP1b proteins at 72 h after dsRNA introduction. Luciferase activities were measured at 72 h post-transfection. Luciferase activities are represented as relative values based on DBD (empty plasmid introduced cells) as a standard. Error bars = SD. The SDs and P-values (determined by the t-test, *P<0.1, **P<0.05, ***P<0.01, which was checked by a comparison with the luciferase activities in the DBD-introduced controls with DBD-HP1a, DBD-HP1b, DBD-Ago3 or DBD-Siwi-introduced cells) are based on n = 3.