Abstract
IntroductionThe function of Glycogen Synthase Kinases 3β (GSK-3β) has previously been shown to be necessary for normal secondary palate development. Using GSK-3ß null mouse embryos, we examine the potential coordinate roles of Wnt and Hedgehog signaling on palatal ossification.MethodsPalates were harvested from GSK-3β, embryonic days 15.0–18.5 (e15.0–e18.5), and e15.5 Indian Hedgehog (Ihh) null embryos, and their wild-type littermates. The phenotype of GSK-3β null embryos was analyzed with skeletal whole mount and pentachrome stains. Spatiotemporal regulation of osteogenic gene expression, in addition to Wnt and Hedgehog signaling activity, were examined in vivo on GSK-3β and Ihh +/+ and −/− e15.5 embryos using in situ hybridization and immunohistochemistry. To corroborate these results, expression of the same molecular targets were assessed by qRT-PCR of e15.5 palates, or e13.5 palate cultures treated with both Wnt and Hedgehog agonists and anatagonists.Results GSK-3β null embryos displayed a 48 percent decrease (*p<0.05) in palatine bone formation compared to wild-type littermates. GSK-3β null embryos also exhibited decreased osteogenic gene expression that was associated with increased Wnt and decreased Hedgehog signaling. e13.5 palate culture studies demonstrated that Wnt signaling negatively regulates both osteogenic gene expression and Hedgehog signaling activity, while inhibition of Wnt signaling augments both osteogenic gene expression and Hedgehog signaling activity. In addition, no differences in Wnt signaling activity were noted in Ihh null embryos, suggesting that canonical Wnt may be upstream of Hedgehog in secondary palate development. Lastly, we found that GSK-3β −/− palate cultures were “rescued” with the Wnt inhibitor, Dkk-1.ConclusionsHere, we identify a critical role for GSK-3β in palatogenesis through its direct regulation of canonical Wnt signaling. These findings shed light on critical developmental pathways involved in palatogenesis and may lead to novel molecular targets to prevent cleft palate formation.
Highlights
The function of Glycogen Synthase Kinases 3b (GSK-3b) has previously been shown to be necessary for normal secondary palate development
We have previously shown that GSK-3b null embryos display complete clefting of the secondary palate
In order to more thoroughly analyze the GSK-3b null embryo palatal phenotype, we performed a whole mount skeletal stain looking at the palatine bones (Figure 1), as the palatine processes of the maxilla and the horizontal lamina of the palatine bones form the secondary palate, which is clefted in the GSK-3b null embryo
Summary
The function of Glycogen Synthase Kinases 3b (GSK-3b) has previously been shown to be necessary for normal secondary palate development. Using GSK-3ß null mouse embryos, we examine the potential coordinate roles of Wnt and Hedgehog signaling on palatal ossification. Craniofacial birth defects, such as cleft lip and/or palate, can cause extensive physical and psychosocial complications, representing a significant socioeconomic burden. GSK-3ß is an important regulator of a number of molecular pathways, such as Wnt, Hedgehog, NFAT, and insulin signaling [1] Of these pathways, the precise regulation of both Wnt and Hedgehog signaling may be necessary for normal craniofacial development, as disruptions in either of these pathways can lead to craniofacial abnormalities, including palatal clefting [3,4,5]
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