Figure 8

Model of salivary gland cellular maturation and duct formation. (A) Lateral lobe maturation. SG secretory cells in newly eclosed adults are nearly cuboidal in shape (A1,B1). Within the first 36 hours post eclosion, a pre-apical compartment (PAC) positive for WGA and secreted proteins forms; vesicles (v) positive for WGA and saliva proteins are also observed (2). Buds of secreted material are observed between the PAC and the growing apical surface/SC (3). PAC fusion to the apical plasma membrane is observed, releasing remaining secretory proteins (3). PAC fusion expands the apical surface of the cell and the SC (4). Continued secretion ultimately leads to massive SC expansion and basal compression of the remaining cellular material (5). By day four, a small periductal space separates the walls of the cup shaped cells from the central duct in the PL but not DL (6). Secretion-positive vesicles are rarely observed intact in the SC and SD, perhaps due to denaturation and/or dilution in the presumptive acidic lumenal compartment. (B) Medial lobe maturation. In the earliest adult SG medial lobes, a fibrous matrix can be observed within part of the lumenal space, and sites of interaction are observed at the apical surface of cells (1). The matrix is continually shrinking in size and loses cell contact, until the matrix is no longer visible and PACs begin to form and fuse to the apical surface (2). At day four post eclosion and beyond, SCs have formed and expanded throughout the SG (3). In cross-section (4), cup shaped cells surround secretory cavities open to the lumen. Lumenal saliva is marked in light purple. Abbreviations: N–nucleus; SC–secretory cavity; PAC–pre-apical compartment; SD–salivary duct; L–lumen.