Fig. 7. Summary and models of phyl in es organ development. (A) The process of es organ development. (B) In phyl mutants, SOP fails to form although the expression of proneural genes is not affected. Also, phyl is required for cell fate specification of IIb cells; IIb cells are transformed to IIa cells in phyl mutants (C). (D,E) Our data suggests that Phyl is expressed in SOP and IIb cells, and functions together with Sina to degrade Ttk. In non-SOP cells (which ultimately become epidermal cells) and IIa cells, the levels of phyl mRNA are down-regulated by N signaling.