Figure 7.

A Schematic Model for EE Specification Driven by the Positive Feedback Regulatory Circuit Composed of Sina/Phyl, Ttk69, and Sc

In EE progenitor cells derived from ISCs, Phyl is upregulated, which links EE-repressor Ttk69 to the E3 ubiquitin ligase Sina for degradation. Ttk69 degradation results in the derepression of AS-C genes, which subsequently induces the expression of EE-determination factor Pros to promote EE specification. The expression of Sc also induces Phyl expression, thereby forming a positive feedback regulatory circuit that continuously drives Phyl expression, Ttk69 degradation, and Pros accumulation, ultimately leading to EE commitment.