ARTICLE |
Correspondence to: Minoru Onozuka, Dept. of Anatomy (2nd Division), Gifu University School of Medicine, 40 Tsukasa-machi, Gifu 500-8705, Japan. E-mail: onozuka@cc.gifu-u.ac.jp
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Summary |
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We studied the involvement of the apoptotic mechanism(s) in cell differentiation in the developing male rat submandibular gland using the TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphatebiotin nick-labeling) assay in combination with light and electron microscopy. Whereas the proacinar cells were completely transformed into acinar cells within 2 weeks after birth, starting on postnatal Day 21, the terminal tubule cells formed vacuoles that disappeared by postnatal Day 35. During this period, positive TUNEL reactivity was seen in the terminal tubule cells, and electron microscopic analysis showed that certain morphological features of apoptosis, including fragmentation of nuclei and the presence of apoptotic bodies in the cytoplasm, were present in and restricted to the terminal tubule cells. These results indicate that, in addition to an autophagocytosis-mediated mechanism, apoptosis may also be involved in reducing the number of terminal tubule cells during postnatal development in the submandibular gland. (J Histochem Cytochem 48:695698, 2000)
Key Words: apoptosis, development, cell differentiation, terminal tubule cells, submandibular gland, TUNEL staining
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Introduction |
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The submandibular gland, an important secretory organ in vertebrates, consists of a terminal portion and a ductal system. In the terminal tubular region of the submandibular gland in the neonatal rat, three different types of cells, terminal tubule cells, proacinar cells, and acinar cells, can be identified on the basis of their histological and ultrastructural features. However, the adult gland contains only acinar cells (
In recent years, apoptosis (programmed cell death) has been implicated as the mechanism responsible for reducing cell numbers during the regression of parenchymal hyperplasia that occurs in many organs during development or cell differentiation (
Male Wistar rats were used at various stages between 7 and 35 days after birth. Morphological aspects of the postnatal development of the submandibular gland were studied by light and electron microscopy, whereas potential apoptotic cells were identified by the TUNEL assay by a conventional immunohistochemical method using an ApopTag Plus in situ apoptosis detection kit (ONCOR; Gaithersburg, MD) according to the manufacturer's instructions.
In agreement with a previous study (
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TUNEL analysis revealed that, during Days 2130 of postnatal development, TUNEL-positive cells were found only in the terminal tubular region (Fig 1Bb-1Be). They were most abundant (about 14% of the total terminal tubule cells) on Day 23 ( Fig 1Bc and 1C), after which their numbers decreased progressively (Fig 1Bd, 1Be and 1C), with no TUNEL-positive cells being detected by postnatal Day 35 ( Fig 1Bf and 1C). Similar experiments, carried out using a very recently published modified in situ TUNEL technique for the improved detection of apoptotic cells (
Several studies have suggested that the original in situ TUNEL assay for apoptosis does not discriminate among apoptosis, necrosis, and autolytic cell death (
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Acknowledgments |
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Supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (08835009 ; 07906320).
Received for publication June 18, 1999; accepted December 10, 1999.
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