Fig. 4

Development of the organisation of basal microfilaments (bMF) in the FCE during S8–12. Tangential optical sections (see Fig. 3) of typical follicles stained with fluorescent phalloidin are shown. Stage-specific features of the bMF-pattern are represented as sketches in the right column. The dotted lines in the middle column (magnifications of boxed areas in the left column) correspond to the lateral FC-membranes seen at a deeper focal plane. Due to cell protrusions close to the basement membrane, the cell borders appear to be shifted. In the cuboidal FC of S8, the preferential bMF-bundle orientation within individual FC as well as relative to neighbouring FC is perpendicular to the follicle’s antero-posterior (a-p) axis. During S9–11, rearrangements of the bMF-organisation occur. In S9, the bMF in the flattening cFC condense (red asterisks), whereas in S10a, the bMF-bundles in cFC are again aligned in parallel perpendicular to the a-p axis, i. e. along the dorso-ventral (d-v) axis. In S10b, condensation followed by disintegration of bMF become obvious in dorsal cFC as well as neighbouring FC, and this pattern spreads out toward the pFC in S11 (crescent-shaped condensations). During S12, a new pattern of dense parallel bMF perpendicular to the a-p axis emerges. In contrast to earlier stages, FC borders are discernible in this focal plane due to chorion ridges. For abbreviations, see legend to Fig. 1. Scale bars refer to all pictures in the same column