Cleft lip and palate are common birth defects and represent a large biomedical burden. Through the use of animal models, the molecular underpinnings of cleft palate are becoming increasingly clear. Indian Hedgheg (Ihh) has been shown to be associated craniofacial development and active in the palatine bone. We hypothesize that Ihh activity plays a role in osteogenesis within the secondary palate and that defects in this pathway may inhibit the osteogenesis of the secondary palate.
Palates were isolated from wild type mice during the period of palate development (e9.5-e17.5). qRT-PCR was used for detecting gene expression during osteogenic differentiation and cellular differentiation (Shh, Ihh, Ptc1, Gli1, Gli2, Gli3, Runx2, Alp, Col1a1). Next, palates were analyzed by H&E, Aniline Blue, Pentachrome, and In situ Hybridization to assess osteogenesis of the palatal shelf and expression of hedgehog pathway genes. Finally, the palate of Indian Hedgehog null mice was analyzed to determine the effect of genetic deficiency on palatal development osteogenesis.
Increased Indian Hedgehog and osteogenic signaling coincided with ossification and fusion of the palate in wild-type mice. This included a 5-150 fold peak in expression of Hedgehog elements, including Ihh, at e15.5 as compared to e9.5. Contrarily, loss of Indian Hedgehog by genetic knockout (Ihh −/−) resulted in decreased secondary palate ossification.
Our results suggest a role for Hedgehog signaling during palatal ossification. The hedgehog pathway is activated during palatal fusion and deletion of Indian hedgehog leads to diminished ossification of the secondary hard palate.
Keywords: Palatal Development, Cleft palate, Indian Hedgehog, Osteogenesis