Cell death during development of intercalated ducts in the rat submandibular gland

Programmed cell death, or apoptosis, occurs during the development of many tissues and organs in almost all multicellular organisms. Although apoptosi s of salivary gland cells has been demonstrated in several pathological con ditions, the role of apoptosis in the postnatal development of the salivary glands is unknown. We have studied the development of the rat submandibula r gland (SMG) during its transition from the perinatal stage to the mature adult stage. Terminal tubule or Type I cells, which synthesize the secretor y protein SMG-C, are prominent in the perinatal acini and are believed to f orm the intercalated ducts of the adult gland. Between 25 days and 30 days after birth, the number of Type I cells and their SMG-C immunoreactivity ma rkedly decreased. Apoptotic cells in association with the developing interc alated ducts were labeled with the Terminal Deoxyribonucleotidyl. Transfera se-Mediated dUTP Nick End Labeling (TUNEL) method. Between 25 and 40 days o f age, from 50 to 80% of the apoptotic cells in cryostat sections of the SM G were closely associated with the intercalated ducts. Electron microscopy showed that the Type I cells became vacuolated, their secretory granules we re reduced in size and number, and the amount of rough endoplasmic reticulu m was decreased. Cellular debris resembling apoptotic bodies was phagocytos ed by macrophages and adjacent intercalated duct cells. These observations suggest that the loss of Type I cells and reduction of SMG-C immunoreactivi ty during development of the intercalated ducts of the adult rat SMG is due , at least in part, to apoptosis. Anat Rec 258:349-358, 2000. (C) 2000 Wile y-Liss, Inc.