Ruffled border of osteoclast: its three dimensional ultrastructure

Area of Science:

• Cell Biology
• Histology
• Biomineralization

Background:

• Osteoclasts are multinucleated cells crucial for bone resorption.
• The ruffled border is a specialized cell membrane structure involved in bone remodeling.
• Understanding the ultrastructure of the ruffled border is key to comprehending bone resorption mechanisms.

Purpose of the Study:

• To three-dimensionally examine the ultrastructure of osteoclast ruffled borders in immature rat bone.
• To characterize the configurations and associated structures of the ruffled border.

Main Methods:

• Scanning and transmission electron microscopy of mandibular bone from newborn Wistar-strain rats.
• Maceration and cytoplasmic matrix extraction using osmium tetroxide for SEM observation.

Main Results:

• Identified three distinct configurations of the ruffled border's membranous invaginations: low/narrow ridges, high/wide ridges, and high/large bulges.
• Observed cytoplasmic projections and coated pits at the summits of high ridges and bulges, suggesting their role in coated vesicle formation.
• Found numerous mitochondria and endocytotic vacuoles within osteoclasts.

Conclusions:

• The ruffled border exhibits complex three-dimensional configurations critical for osteoclast function.
• Coated vesicles likely originate from specific regions of the ruffled border, implicating them in endocytosis during bone resorption.