Circadian Mitotic Rhythms in the Cervical Tissues of the Rat Maxillary Incisor

Kiely, Michael L.; Wilde, J

doi:10.1177/00220345740530062401

J Dent Res

1974

DOI: 10.1177/00220345740530062401

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Circadian Mitotic Rhythms in the Cervical Tissues of the Rat Maxillary Incisor

Michael L. Kiely

J Wilde

Abstract: A pronounced 24-hour fluctuation occurs in the mitotically active tissues of the rat maxillary incisor. High and low periods of activity were seen during the daytime as well as at night. A consistent increase in the number of mitotic figures occurred approximately four hours subsequent to a change in the light-dark regimen.

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Cited by 9 publications

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“…At the base of the forming tooth, cells of the inner enamel epithelium arise from the cervical loop, a reservoir of stem cells that develops into ameloblast precursors (Thesleff et al, 2007). Daily mitotic rhythms have been observed in epithelial cells at the apical loop of rat incisors (Kiely and Wilde, 1974; Gasser et al, 1972). …”

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confidence: 99%

The Circadian Clock Modulates Enamel Development

et al. 2012

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Fully mature enamel is about 98% mineral by weight. While mineral crystals appear very early during its formative phase, the newly secreted enamel is a soft gel-like matrix containing several enamel matrix proteins of which the most abundant is amelogenin (Amelx). Histological analysis of mineralized dental enamel reveals markings called cross-striations associated with daily increments of enamel formation, as evidenced by injections of labeling dyes at known time intervals. The daily incremental growth of enamel has led to the hypothesis that the circadian clock might be involved in the regulation of enamel development. To identify daily rhythms of clock genes and Amelx, we subjected murine ameloblast cells to serum synchronization to analyze the expression of the circadian transcription factors Per2 and Bmal1 by real-time PCR. Results indicate that these key genetic regulators of the circadian clock are expressed in synchronized murine ameloblast cell cultures and that their expression profile follows a circadian pattern with acrophase and bathyphase for both gene transcripts in antiphase. Immunohistological analysis confirms the protein expression of Bmal and Cry in enamel cells. Amelx expression in 2-day postnatal mouse molars dissected every 4 hours for a duration of 48 hours oscillated with an approximately 24-hour period, with a significant approximately 2-fold decrease in expression during the dark period compared to the light period. The expression of genes involved in bicarbonate production (Car2) and transport (Slc4a4), as well as in enamel matrix endocytosis (Lamp1), was greater during the dark period, indicating that ameloblasts express these proteins when Amelx expression is at the nadir. The human and mouse Amelx genes each contain a single nonconserved E-box element within 10 kb upstream of their respective transcription start sites. We also found that within 2 kb of the transcription start site of the human NFYA gene, which encodes a positive regulator of amelogenin, there is an E-box element that is conserved in rodents and other mammals. Moreover, we found that Nfya expression in serum-synchronized murine ameloblasts oscillated with a strong 24-hour rhythm. Taken together, our data support the hypothesis that the circadian clock temporally regulates enamel development.

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The Circadian Clock Modulates Enamel Development

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Quantitative analysis of cell turnover in the enamel organ of the rat incisor. Evidence for ameloblast death immediately after enamel matrix secretion

1977

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During renewal of the enamel organ in the rat incisor cohorts of epithelial cells are transported sequentially through presecretory, secretory and maturation zones to the gingival margin where the life cycles of these cells terminate. This process was examined kinetically by determining the absolute flux of cells within each of these zones of amelogenesis. It was found that the efflux of ameloblasts, stratum intermedium and papillary layer cells from the presecretory zone was about equal to the efflux plus expected growth within the secretory zone. However, between the secretory and maturation zones about 50% more ameloblasts entered the maturation zone than were required to account for the egress at the gingival margin and the expected growth. Since there was no similar imbalance between these zones for papillary layer cells, it was concluded that this discrepancy must represent a 50% reduction in the size of the ameloblast population during the maturation stage of amelogenesis. It was calculated that a little over 25% of the loss occurred immediately at the start of maturation within the region of postsecretory transition and the remaining 25% of the loss occurred throughout the subsequent regions of the maturation zone. In addition to the kinetic analysis graphic reconstructions, or surface maps, of ameloblast nuclei were prepared. These maps illustrated the characteristics of ameloblast nuclear packing within the three zones of amelogenesis and they provided quantitative confirmation that as ameloblasts progress through the maturation zone, there is a loss of cells in an amount predicted by the kinetic analysis.

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Acceleration and circadian rhythm of eruption rates in the rat incisor

Chiba¹,

Tashiro²,

Tsuruta

et al. 1976

Archives of Oral Biology

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Circadian Mitotic Rhythms in the Cervical Tissues of the Rat Maxillary Incisor

Cited by 9 publications

References 25 publications

The Circadian Clock Modulates Enamel Development

The Circadian Clock Modulates Enamel Development

Quantitative analysis of cell turnover in the enamel organ of the rat incisor. Evidence for ameloblast death immediately after enamel matrix secretion

Acceleration and circadian rhythm of eruption rates in the rat incisor

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