Abstract
Cleft palate is one of the most common congenital birth defects worldwide. The homeobox (Hox) family of genes are key regulators of embryogenesis, with Hoxa2 having a direct role in secondary palate development. Hoxa2−/− mice exhibit cleft palate; however, the cellular and molecular mechanisms leading to cleft palate in Hoxa2−/− mice is largely unknown. Addressing this issue, we found that Hoxa2 regulates spatial and temporal programs of osteogenic differentiation in the developing palate by inhibiting bone morphogenetic protein (BMP) signaling dependent osteoblast markers. Expression of osteoblast markers, including Runx2, Sp7, and AlpI were increased in Hoxa2−/− palatal shelves at embryonic day (E) 13.5 and E15.5. Hoxa2−/− mouse embryonic palatal mesenchyme (MEPM) cells exhibited increased bone matrix deposition and mineralization in vitro. Moreover, loss of Hoxa2 resulted in increased osteoprogenitor cell proliferation and osteogenic commitment during early stages of palate development at E13.5. Consistent with upregulation of osteoblast markers, Hoxa2−/− palatal shelves displayed higher expression of canonical BMP signaling in vivo. Blocking BMP signaling in Hoxa2−/− primary MEPM cells using dorsomorphin restored cell proliferation and osteogenic differentiation to wild-type levels. Collectively, these data demonstrate for the first time that Hoxa2 may regulate palate development by inhibiting osteogenic differentiation of palatal mesenchyme via modulating BMP signaling.
Highlights
Cleft palate is one of the most common structural birth defects in humans with an incidence of 1 in 700–1,000 live births (Dixon et al, 2011)
In the posterior region of the hard palate, Alkaline Phosphatase I (ALPI) staining was present in the ossifying centers of the palatal process of the palatine bone in wild-type embryos (Figures 1C,G), whereas there was an expansion in the expression domain of ALPI positive preosteoblasts toward the oral side in Hoxa2−/− embryos (Figures 1D,H)
The expression of SP7, a downstream target of RUNX2 and a marker of mature osteoblasts, was not increased in the Hoxa2−/− palate (Figure 1P) compared to wild-type (Figure 1O). This suggests that cells toward the oral side of the palatal process of the palatine bone are at immature osteoblast stage and may not have developed bone matrix by E16.5
Summary
Cleft palate is one of the most common structural birth defects in humans with an incidence of 1 in 700–1,000 live births (Dixon et al, 2011). Studies using mouse model which has a high similarity to human palate development helped to identify several key stages and cellular processes during palate formation (Yu et al, 2017). The Abbreviations: AlpI, alkaline phosphatase I; ARS, Alizarin red S; BMP, bone morphogenetic protein; CNCC, cranial neural crest cells; d, day; E, embryonic day; MEPM, mouse embryonic palatal mesenchyme; pSMAD 1/5/8, phosphorylated SMAD 1/5/8; qRT-PCR, quantitative real-time PCR; Runx, runt-related transcription factor 2. The palatal shelves on either side contact each other forming midline epithelial seam at E14.5, which eventually disintegrates leading to palatal fusion by E15.5 (Kaufman, 1992). While the structural changes during palate development are well defined, there is a scarcity of knowledge on the molecular mechanisms governing the patterning of the palate
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
