Fig. 6. Changes of F-actin organization in the end apparatus and the nuclear morphology of secretory cells.

Hypopharyngeal glands of bumblebee workers from different pupal stages ((A) P5 stage, dark eyes, light cuticle; (B) P6/P7, dark eyes and cuticle), and from young adults ((C) <2 hours post eclosion; (D) ∼8 hours post eclosion) were dissected, treated with Hoechst stain (blue) and fluorescently labeled phalloidin (green). (A) The F-actin tubes of the end apparatus begin to arise (red arrows), nuclei are largely round-shaped. (B) More advanced stage of actin tubes formation, septum membrane not delivered, nuclei still round. (C) Septum membrane delivered by directed exocytosis, freshly secreted septal cuticle solidifies, microvilli of the septum held in shape by cortical F-actin (yellow arrows), nuclei become deformed. (D) Septal cuticle solidified, underlying cortical F-actin depolymerizes, shapes of nuclei remain deformed. All figures are at the same magnification. Scale bar: 20 µm.