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Postnatal expansion of the intramembranous bones of the craniofacial skeleton occurs as bone growth at sutures. Loss of the bone growth site occurs when the suture fails to form, or when the newly formed sutures become ossified, resulting in premature obliteration. Previous experiments demonstrated that removal of dura mater from fetal rat coronal sutures, or neutralizing transforming growth factor-beta 2 (Tgf-␤2) activity using antibodies resulted in premature obliteration of the suture in vitro. Conversely, addition of Tgf-␤3 to coronal sutures in vitro rescued them from osseous obliteration. To examine whether Tgf-␤3 rescues sutures from obliteration in vivo, a collagen gel was used as a vehicle to deliver Tgf-␤3 to the normally fusing rat posterior interfrontal (IF) suture. Surgery was done on postnatal day 9 (P9) rats, in which collagen gels containing 0, 3, or 30 ng Tgf-␤3 were placed above the IF suture, underneath the periosteum for 2 weeks. By P24, 75-100% of animals in control unoperated, sham-operated, and collagen gel-only groups had fused IF sutures. In contrast, 40% of sutures exposed to 3 ng Tgf-␤3 remained open, while sutures exposed to 30 ng Tgf-␤ were similar to controls. By immunohistochemistry, sutures rescued from obliteration by Tgf-␤3 had the same Tgf-␤ receptor type II (T␤r-II) distribution as controls. However, Tgf-␤3-treated sutures had altered Tgf-␤2 and T␤r-I distribution compared to controls. Anat Rec 267: 120 -130, 2002.

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