Fig. 1.

EcR signalling controls expression of the EcR gene during oogenesis. Schematic representation of a single ovariole containing a string of developing egg chambers of progressive age (a). The newly formed egg chamber emerges from the germarium, undergoes a continuous process of development and acquires morphological features that allow recognition of 14 different stages. In each egg chamber FCs form an epithelium that covers the nurse cells–oocyte complex. As oogenesis proceeds, complex differentiation events specify multiple subpopulation of FCs. Starting at stage 9 a group of anterior follicle cells, the border cells, delaminates from the epithelium and migrates through the nurse cells to reach the oocyte surface. As egg chamber grows, main body FCs change their shape from cuboidal to columnar and by stage 10 they cover the oocyte. The organisation of the stage 10B is illustrated in the schematic drawings of a sagittal plane through the centre of the egg chamber and of a surface view. At stage 10B few squamous FCs cover the nurse cells, the columnar main body FCs surround the oocyte and a group of anterior columnar FCs, namely the centripetally migrating FCs, starts to migrate at the interface between the oocyte and the nurse cells. The border cells after reaching the anterior region of the oocyte start to migrate dorsally. Anterior is to the left. The FC flp-out clones are marked by the expression of the GFP protein (green, dotted area in b–d). Confocal microscopy analysis of stage 10B egg chambers dissected from hs-flp/Act>>Gal4; UAS-nGFP/+; UAS-EcRB2-F645A/+ females (b–d) and stained with anti-EcRA (red in b), anti-EcRB1 (red in c) and anti-EcR common (red in d), antibodies. The stage 10B egg chambers are oriented with the anterior regions to the left. Scale bars b–d 50 μm