The pivotal role of CCN2 in mammalian palatogenesis

Abstract

Mammalian palatogenesis is a complex process involving a temporally and spatially regulated myriad of factors. Together these factors control the 3 vital processes of proliferation, elevation and fusion of the developing palate. In this study, we show for the first time the unequivocally vital role of CCN2 in development of the mammalian palate. We utilized CCN2 knockout (KO) mice and cranial neural crest derived mesenchymal cells from these CCN2 KO mice to investigate the 3 processes crucial to normal palatogenesis. Similar to previously published reports, the absence of CCN2 inhibits proliferation of cells in the palate specifically at the G1/S transition. Absence of CCN2 also inhibited palatal shelf elevation from the vertical to horizontal position. CCN2 KO mesenchymal cells demonstrated deficiencies in adhesion and spreading owing to an inability to activate Rac1 and RhoA. On the contrary, CCN2 KO mesenchymal cells exhibited increased rates of migration compared to WT cells. The addition of exogenous CCN2 to KO mesenchymal cells restored their ability to spread normally on fibronectin. Finally, utilizing an organ culture model we show that the palatal shelves of the CCN2 KO mice demonstrate an inability to fuse when apposed. Together, these data signify that CCN2 plays an indispensible role in normal development of the mammalian palate and warrants additional studies to determine the precise mechanism(s) responsible for these effects.

Development of Normal and Cleft Palate: A Central Role for Connective Tissue Growth Factor (CTGF)/CCN2

“…CCN2 was first documented to play a role in palate development while characterizing its role in bone development [ 5 ]. Further studies showed more extensive involvement in craniofacial bone formation and altered underlying signaling [ 6 , 7 ]. We also discuss a number of other important factors that have been previously shown to regulate palate development as well as their interactions with CCN2.…”

“…Extensive phenotypic analysis reveals that despite these differences, the two models are remarkably similar [ 5 , 60 ]. Although CCN2 KO animals appear to die of hypoxia within minutes after birth, they do complete the embryonic developmental process [ 5 , 7 ]. Other characteristic defects observed in both models include lung hypoplasia, various craniofacial morphological changes, reduced chondrocyte proliferation in long bone growth plates, and distinct kinking of the ribs, radii, ulnae, and tibias [ 5 , 6 , 60 ].…”

“…Although these studies of CCN2 KO mice alluded to a cleft palate phenotype, the mechanisms were unknown [ 5 , 6 ]. A more recent study utilizing CCN2 KO mice and cranial neural crest-derived mesenchymal cells from these mice provided unequivocal evidence for the vital role of CCN2 in palate development [ 7 ]. The three processes that are essential for normal palate development, namely growth (proliferation), elevation and fusion of the palatal shelves, are all negatively affected in CCN2 KO mice [ 7 ].…”

“…A more recent study utilizing CCN2 KO mice and cranial neural crest-derived mesenchymal cells from these mice provided unequivocal evidence for the vital role of CCN2 in palate development [ 7 ]. The three processes that are essential for normal palate development, namely growth (proliferation), elevation and fusion of the palatal shelves, are all negatively affected in CCN2 KO mice [ 7 ]. The absence of CCN2 inhibits the proliferation of palate mesenchymal cells specifically at the G1/S transition [ 7 ].…”

“…The three processes that are essential for normal palate development, namely growth (proliferation), elevation and fusion of the palatal shelves, are all negatively affected in CCN2 KO mice [ 7 ]. The absence of CCN2 inhibits the proliferation of palate mesenchymal cells specifically at the G1/S transition [ 7 ]. Absence of CCN2 also inhibits elevation of the palatal shelves from the vertical to horizontal position [ 7 ].…”