Morphometric analysis of the nucleolus during the life cycle of human odontoblasts

Abstract

Developing first premolars were used as a model system to obtain information on the nucleolar structure of human odontoblasts at several stages of their life cycle. Four stages were defined by their location within the tooth: a) preodontoblasts were located at the growing tip of the root; b) secretory odontoblasts in the apical region; c) transitional odontoblasts in the middle region; and d) aged odontoblasts in the coronal region. Preodontoblasts have a small nucleolus (0.55 micron 2) with few strands of dense fibrillar material radiating from the fibrillar center. Secretory odontoblasts are characterized by a large (1.24 micron 2), irregular, and reticulated nucleolus. The fibrillogranular material, the largest component in all nucleoli, reaches maximal size at this stage (0.88 micron 2). Fibrillar centers occupy about the same area (0.1 micron 2) throughout the odontoblast's life cycle. As the formation of primary dentin is completed, the nucleolus of transitional odontoblasts is reduced in size (0.54 micron 2). Finally, the aged odontoblasts have a small, compact nucleolus (0.39 micron 2), with segregated components. Morphologic analysis and quantification of size and component areas of nucleoli obtained with an image analyzer indicated that secretory odontoblasts had the most active, and aged odontoblasts the least active, nucleolus.

Expression of Dynamin II in Odontoblast During Mouse Tooth Development

“…Secretory odontoblasts have active potential for protein synthesis due to the presence of distinct organelles, such as well-developed rER, Golgi complex, secretory vesicles and mitochondria. 20 Dentin formation begins at the advanced bell stage, between PN1 and PN5 in this study. 2 At this stage, the morphology of the odontoblasts shows polarity due to reorganization of the cytoskeleton and organelles, and the length of the cells is elongated.…”

Autophagic Activity and Aging in Human Odontoblasts

“…Once primary dentinogenesis is completed, the odontoblast reduces its secretory machinery by autophagic activity and limits its secretory functionality (Couve, 1986, 1987). This last cellular stage has been characterized as a resting odontoblast condition (Couve, 1985, 1986; Linde and Goldberg, 1993; Ten Cate, 1994). After the active period of primary dentinogenesis, resting odontoblasts maintain their physiological secretory activity, forming secondary dentin, and are capable of responding to moderate injury by the formation of reactionary dentin ( e.g ., caries lesions of slow progression) (Smith et al ., 1995; Murray et al ., 2000, 2003; Bjorndal and Mjör, 2001).…”