Temporal Changes in Gene Expression of Mouse Posterior Frontal Suture

Objectives: Mice are a commonly studied model of cranial suture closure because the posterior frontal (PF) suture fuses early in development. The objective of this study was to identify genes that are responsible for the development of the PF suture. Methods: Under approval of the Georgia Tech IACUC, nine C57Bl/6J mice/day were euthanized on days 6, 9, 12, 20, 25, and 50, based on our previous analysis of the complete time course of PF suture fusion. RNA was extracted from the PF suture and gene expression was screened using osteogenesis PCR arrays. Genes showing greater than threefold change were confirmed by real-time qPCR. Results: The PCR array showed 28 out of the 96 genes had significant changes in expression. After qPCR confirmation, mRNAs for genes related to osteoblast differentiation (OCN, Runx2) increased on days 25 and 50, corresponding to suture mineralization. TGFB2 and TGFB3 mRNAs increased immediately preceding suture fusion (day 9). Genes associated with cartilage development (ColX, ColII, COMP) had increased expression during the onset of fusion (day 12). BMP2 expression was relatively constant over the entire time course whereas BMP4 was reduced on day 16. Expression of BMP inhibitors increased immediately preceding suture fusion (BMP3), at the beginning of fusion (sclerostin), and later during mineralization (gremlin1), or remained relatively constant (chordin, noggin). Conclusions:  The presence of cartilage associated genes early in suture fusion supports the hypothesis that suture fusion occurs by endochondral ossification. Increased expression of osteoblast differentiation markers occurred during the increase in suture mass by µCT. The lack of large changes in the BMP2 and noggin, suggest that these genes may not play as significant a role as previously reported. Most interestingly, other BMP inhibitors had very distinct expression profiles, indicating multiple inhibitors are involved in regulating PF suture fusion. (Supported by Children's Healthcare of Atlanta.)