Immunohistochemical assessment of cranial suture development in rats

The present study investigated, by immunohistochemistry, the postnatal occurrence and anatomical localisation of some bone and cartilage proteins and proteoglycans in the rat coronal sutural region. Thirty two Sprague-Dawley rats, four in each group, were killed at ages 3, 5, 8, 10, 15, 30, 50 and 100 days and the sutural region subsequently subjected to histological examination. The biochemical constituents investigated were: 36 kDa, 58 kDa, 59 kDa, 62 kDa, 148 kDa, 400 kDa proteins, chondrocalcin, bone sialoproteins I and II (BSP I and II), osteopontin (ost I), small cartilage 1 and 2 as well as large cartilage proteoglycans (PG-S1, PG-S2, PG-LA). Standard haematoxylin-eosin and laminin staining was also carried out. In general, detectable constituents were visualized until Day 50. Labelling of the proteins 59 kDa protein, BSP I and II, and ost I was distinct along the sutural bone margins and, initially, cells and fibrillar structures within the sutural ligament were also labelled. The 58 kDa protein was localised unspecifically to the suture tissue proper at Days 50 and 100. PG-S1 labelling was concentrated primarily at the sutural edge. Remaining substances were indistinguishable throughout the entire observation period. The dual response of proteoglycans in bone mineralisation and the potential importance of cartilaginous tissue in sutural closure is discussed.