Method of Studying Palatal Fusion using Static Organ Culture

In Vitro Analysis of Palatal Shelf Elevation During Secondary Palate Formation

Palatal shelf elevation is an essential morphogenetic process during secondary palate formation. It has been proposed that shelf elevation results from an intrinsic elevating force and is regulated by extrinsic factors that are associated with development of other orofacial structures. Although dynamic palate culture is a common in vitro approach for studying shelf elevation, it requires the tongue or the tongue and mandible to be removed before culture, which prevents any determination of the role of the extrinsic factors in regulating shelf elevation. We showed that ex vivo removal of the tongue and mandible from unfixed embryonic heads led to spontaneous shelf movements that were more pronounced at late E13.5 and early E14.5 than those of E12.5 and early E13.5, suggesting that the strength of the elevating force increases over time during palate development. We further used a suspension culture technique to analyze palatal shelf movement in an intact oral cavity by culturing the orofacial portion of embryonic heads that include the maxilla, palatal shelves, mandible, and tongue (MPMT). MPMT explants were cultured in the serum-free medium with slow rotation for 24-48 hr. The palatal shelves successfully elevated during culture and displayed intermediate morphologies that closely resemble those of in vivo shelf elevation. We demonstrate that the tongue and mandible facilitate shelf medial movement/growth during shelf elevation and further suggest that the interaction of the palatal shelves and tongue could be one of the extrinsic factors that regulate the elevation process. Anat Rec, 302:1594-1604, 2019. © 2019 American Association for Anatomy.

Wnt signaling in orofacial clefts: crosstalk, pathogenesis and models

Diverse signaling cues and attendant proteins work together during organogenesis, including craniofacial development. Lip and palate formation starts as early as the fourth week of gestation in humans or embryonic day 9.5 in mice. Disruptions in these early events may cause serious consequences, such as orofacial clefts, mainly cleft lip and/or cleft palate. Morphogenetic Wnt signaling, along with other signaling pathways and transcription regulation mechanisms, plays crucial roles during embryonic development, yet the signaling mechanisms and interactions in lip and palate formation and fusion remain poorly understood. Various Wnt signaling and related genes have been associated with orofacial clefts. This Review discusses the role of Wnt signaling and its crosstalk with cell adhesion molecules, transcription factors, epigenetic regulators and other morphogenetic signaling pathways, including the Bmp, Fgf, Tgfβ, Shh and retinoic acid pathways, in orofacial clefts in humans and animal models, which may provide a better understanding of these disorders and could be applied towards prevention and treatments.

Biglycan and Decorin Expression and Distribution in Palatal Adhesion

Previous studies demonstrated that chondroitin sulfate proteoglycans (CSPGs) on apical surfaces of palatal medial edge epithelial (MEE) cells were necessary for palatal adhesion. In this study, we identified 2 proteoglycans, biglycan and decorin, that were expressed in the palatal shelves prior to adhesion. In addition, we established that these proteoglycans were dependent on transforming growth factor β (TGFβ) signaling. Laser capture microdissection was used to collect selected palatal epithelial cells from embryonic mouse embryos at various palate development stages. The expression of specific messenger RNA (mRNA) for biglycan and decorin was determined with quantitative real-time polymerase chain reaction. The TGFβrI kinase inhibitor (SB431542) was used in palatal organ cultures to determine if blocking TFGβ signaling changed biglycan and decorin distribution. Immunohistochemistry of both biglycan and decorin revealed expression on the apical and lateral surfaces of MEE cells. Biglycan protein and mRNA levels peaked as the palatal shelves adhered. Decorin was less abundant on the apical epithelial surface and also had reduced mRNA levels compared to biglycan. Their proteins were not expressed on MEE cells of palates treated with SB431542, an inhibitor of TGFβ signaling. The temporal expression of biglycan and decorin on the apical surface of MEE, combined with the evidence that these proteins were regulated through the TGFβ pathway, indicated that they may be important for adhesion.