Fig. 4

Differentiation of hypopharyngeal gland during the first half of pupal life. Glands were isolated, fixed, labeled with phalloidin (green) and DAPI (blue), and imaged by confocal serial sectioning. In the case of phalloidin images, gamma correction was set to 0.5 to visualize areas of faint staining. a-d Sagittal sections through the gland epithelium or acini at the developmental stages as indicated. Lumen of the gland primordium or the collecting duct is indicated by asterisks. e-l Horizontal optical sections through the epithelial layer or acini. Dashed lines in a-d indicate relative positions of section planes. At P1 (a,e,i), the hypopharyngeal gland primoridium is composed of a pseudostratified columnar epithelium with mitotic cells (arrowheads) in the apical region. Flask-like cells have their nucleus in the basal half and a narrow process (white arrows) extending toward the gland lumen. The area outlined by a dashed line is presented at higher magnification in the inset (green, no gamma correction). Intense phalloidin staining at the apicolateral side (orange arrows) indicates junctional complexes; the fainter staining between and above the apicolateral sides suggests the presence of microvilli. From P2-P4 on, F-actin-rich tubulous structures (red arrowheads) extend in bundles from the gland lumen basally and are wrapped by two to three concentric rings of cell processes (yellow arrowheads). Future secretory cells (circles) have a large nucleus in the basal region and are as yet devoid of canaliculus-like structures. At P5, the gland is organized into acini that are connected by bundles of ductules (broad arrows) to the collecting duct (asterisk). Future secretory cells (circles) contain an F-actin-rich tubulous structure, the future canaliculus (yellow arrowheads in l). Bars, 20 μm