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Abstract
Introduction
A cleft palate is a common birth defect in humans with an incidence of 1/500 to 1/1,000 births. It appears to be caused by multiple genetic and environmental factors during palatogenesis. Many molecules are involved in palate formation but the biological mechanisms underlying the normal palate formation and cleft palate are unclear. Accumulating evidence suggests that transforming growth factor β /bone morphogenetic proteins (TGF-β /BMP) family members mediate the epithelial-mesenchymal interactions during palate formation. However, their roles in palatal morphogenesis are not completely understood.
Materials and Methods
To understand the roles of TGF-β /BMP signaling in vivo during palatogenesis, mice with a palatal mesenchyme- specific deletion of Smad4, a key intracellular mediator of TGF-β /BMP signaling, were generated and analyzed using the Osr2Ires-Cre mice.
Results
The mutant mice were alive at the time of birth with open eyelids and complete cleft palate but died within 24 hours after birth. In skeletal preparation, the horizontal processes of the palatine bones in mutants were not formed and resulted in a complete cleft palate. At E13.5, the palatal shelves of the mutants were growing as normally as those of theirwild type littermates. However, the palatal shelves of the mutants were not elevated at E14.5 in contrast to the elevated palatal shelves of the wild type mice. At E15.5, the palatal shelves of the mutants were elevated over the tongue but did not come in contact with each other, resulting in a cleft palate.
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Fig. 1.
Phenotypes of Osr2Ires-Cre mediated Smad4 conditional knockout mouse at birth. In contrast to heterozygous littermates A, B, E, mutant mice were born with open eyelid and complete absence of palatal bone C, D, F. In histological analysis, cleft palate (arrow) and open eyelid (∗) was found in the mutant F.
Fig. 2.
Histological features of palate in Osr2Ires-Cre mediated Smad4 conditional knockout mouse during palatogenesis. At E13.5, palatal shelves both of mutant and heterozygous littermates showed inferomedial direction A, B. At E14.5, palatal shelves of heterozygous mice elevated and fused each other C but those of mutant showed vertical orientation D. At E15.5, palatal processes were fused in heterozygous, whereas complete cleft palate were shown in mutant mice E, F.
Fig. 3.
Comparison of tissue specific Smad4 conditional knockout mice in the epithelium or mesenchyme of palatal shelves using K14-Cre or Osr2Ires-Cre mice. Palate was formed normally in the wild type and K14-Cre mediated Smad4 conditional knockout mice A, B, D, E but complete cleft palate was found in the Osr2Ires-Cre mediated Smad4 conditional knockout mouse C, F. Note asterisk marked absence of palatal bone and arrows indicate the medial border of palatal bones.
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