Surface structures and osteoclasts of mouse parietal bones: a light and scanning electron microscopic study

Area of Science:

• Bone Biology
• Cell Biology
• Skeletal Development

Background:

• Osteoclast-mediated bone resorption is crucial for skeletal remodeling and growth.
• Howship's lacunae are microscopic depressions on bone surfaces, traditionally associated with osteoclast activity.
• The precise relationship between osteoclast function and the detailed morphology of resorption surfaces, beyond Howship's lacunae, remains unclear.

Purpose of the Study:

• To investigate the relationship between osteoclast function and the morphological characteristics of bone resorption surfaces.
• To clarify the nature of resorption surfaces observed via scanning electron microscopy (SEM) in relation to Howship's lacunae.

Main Methods:

• Scanning electron microscopy (SEM) was employed to examine the surface structures of parietal bones in mice from newborn to adult stages.
• Morphological analysis focused on identifying and characterizing resorption surfaces and their relationship with osteoclasts.

Main Results:

• The inner surface of the parietal bone exhibited both smooth and rough areas, with rough areas being significantly larger than typical Howship's lacunae.
• Rough areas consisted of numerous small, shallow concavities with ridged borders.
• The extent of rough areas and the number of osteoclasts on the inner skull surface correlated with skull growth rate, peaking around 1 week of age.

Conclusions:

• Osteoclasts resorb bone by migrating across the surface, creating small concavities that form larger rough areas, not solely defined by Howship's lacunae.
• The size, distribution, and morphology of these rough areas and their concavities are dynamic and reflect the functional activity of osteoclasts.