Transcription-dependent polyadenylation signal activity contributes to transcriptomic regulation during Forskolin-induced BeWo cell syncytialization.

Polyadenylation, a core transcriptional step governed by polyadenylation signals (PAS), functionally interacts with transcription. Nevertheless, how PAS sequences respond to variable transcriptional output remains poorly characterized. Here, we precisely modulated cellular transcription levels by integrating SV40 promoter truncation with a Tet-On dual-luciferase reporter system. Diminished polyadenylation efficiency accompanies lowered promoter activity, and graded transcription assays revealed a tiered PAS processing model: canonical and suboptimal PASs maintain stable 3'-end processing at high transcription levels, whereas non-canonical PASs display compromised processing efficiency with rising transcription. During forskolin(FSK)-induced BeWo cell syncytialization, endogenous trophoblast fusion genes carrying potent canonical PASs were selectively mobilized upon transcriptional activation to enrich differentiation transcripts and sustain orderly syncytiotrophoblast maturation. Together, these findings reveal a hierarchical transcription-polyadenylation axis that associate with placental trophoblast syncytialization. They fill key gaps in mRNA processing and provide a foundation for studying the transcriptional regulatory mechanisms underlying trophoblast differentiation.