Nuclear size as a cell‐kinetic marker for osteoblast differentiation

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Abstract
A nuclear morphometic assay for preosteoblasts is introduced as a cell‐kinetic technique, applicable to routine histological preparations of mineralized tissue. Because this method is a morphological marker for osteoblast precursor cell differentiation, it provides a new dimension for determining the mechanism of osteoblast histogenesis. Osteoblast precursors of the periodontal ligament are a mixed population of progenitors, kinetically separable into two distinct groups according to nuclear size. Preosteoblasts, the immediate proliferating precursors of osteoblasts, have large nuclei (>170 μm3) and are derived from relatively undifferentiated fibroblastlike cells, which have smaller nuclei (3). Increase in nuclear volume, during G 1 phase of the cell cycle, is apparently a morphological manifestation of change in genomic expression. This key event in preosteoblast differentiation is related to mechanical stress/strain and may be an important rate‐limiting step in osteoblast histogenesis.