Eyes-absent as marker for the switch from regular mitosis to endocycle. (A-G) Wildtype ovariole stained for f-actin with Phalloidin (red), DNA with Hoechst (blue), and for a cross reacting antibody against Eyes-absent (Eya) (yellow). Panels B-E are close ups of the ovariole shown in A. (E) The Eya pattern is shown in green. In (F) only the Eya channel and in (G) only the Hoechst channel is shown. Panels (G1-G2) are close ups of the ovariole shown in (F,G); nuclei stained for Hoechst and Eya. (A) Eya is expressed in germline derived cells of the tropharium and in a subset of somatic cells. (B-E) In the vitellarium, Eya expression first can be observed upon pro-oocyte encapsulation. Pre-follicular cells, which successively encapsulate the oocytes to form an egg-chamber, start expressing Eya at high levels (B-D; arrowhead, arrow). Note that pro-oocytes are also Eya positive (asterisk in B-D). Subsequently, all follicle cells express Eya. Interestingly, Eya is absent from somatic plug cells (SP) (D,E). (F-G) During mitotic stages, Eya is continuously expressed at high levels (F, G1). At the time follicle cell cease mitosis and enter the endocycle, follicle cell nuclei increase in size and are no longer columnar, but rather round (compare G1 to G2). At that time Eya signals get significantly weaker(F, compare G1 to G2). Hence, only mitotically active follicle cells express Eya at high levels.