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Fig. 4. Actin isoform incorporation into ring canals and actin cages. Using the nanosVP16-Gal4 driver all six actins were expressed in the germline during oogenesis. (A-F') Confocal sections through germaria of GFPactin-expressing ovarioles showing actin incorporation into ring canals. In the colour panels, GFPactins are green, labelling with phalloidin is red (A-F) and the individual GFPactin channels are shown as black and white images (A'-F'). Arrows in A'-F' indicate individual ring canals. (G,H) High levels of actin overexpression can disrupt cyst formation during oogenesis. Overexpression of either actin5C or actin57B in the germline resulted in a fraction of ovarioles failing to form cysts containing 16 cells. The actins localized to cell cortices and ring canals, but these ring canals appeared to contain excess actin and cystocytes were multinucleate (G; GFPactin is shown in green, phalloidin in red and DNA labelled with TOTO-3 is blue; the arrow indicates a ring canal). Despite the reduced cell number, several stage 10-11 egg chambers showed a morphologically distinct oocyte (H; GFPactin is in green, phalloidin in red; the numbers indicate the three nurse cells of this egg chamber, the asterisk denotes the oocyte). (I-O') Confocal sections through the nurse cell part of a stage 10B egg chamber. Egg chambers at this stage, prior to dumping of their cytoplasmic contents into the oocyte, develop a specialized array of actin filaments, `cages', around each nurse cell nucleus. GFPactins are incorporated to varying degrees into these actin cages, e.g. actin87E being incorporated very strongly (N,N') and actin79B only being incorporated at a very low level (M,M'). In the colour panels, GFPactins are green, labelling with phalloidin is red (I-O) and the individual GFPactin channels are shown as black and white images (I'-O').
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