Role of the osteoclast in cranial suture waveform patterning

This study investigates the role of bone resorption in defining interdigitations characteristic of cranial suture waveform. Male mice from the CD-1 (ICR) background were analyzed at six age groups (n = 5 mice per group) in order to study the ontogenetic changes of osteoclast counts using tartrate-resistant acid phosphatase-stained histological sections of sagittal sutures. Additionally, the complexity of suture lines were measured ectocranially from the same age groups (n = 5 per group) using image capture and fractal geometry (ruler dimension method). The results suggest that osteoclast resorption is a contributor to suture patterning. Specifically, osteoclasts show the greatest activity along concave suture regions at 42 and 84 days (Kruskal-Wallis test statistic = 14.9; P <= 0.01). This coincides with significant increases incrementally in suture complexity as measured with fractal dimension at 42 and 84 days of age (ANOVA F-statistic = 19.84; P <= 0.001). In congruence with these data, mice given osteoclast-depleting injections of alendronate show a decrease in sagittal suture complexity. Data from this experiment indicate a positive relationship between suture complexity and osteoclast count (P < 0.01; r = 76%). Increases in suture complexity and osteoclast activity occur after peak rates of cranial width growth and coincide with weaning and the transition to a hard chow diet. These data demonstrate osteoclasts along the bone margin of the cranial suture and also indicate that sutures attain their complex shape at the same age when osteoclast number is highest along concave suture margins, underscoring the role of osteoclasts in generating the suture waveform pattern.