Movement of palatal shelves during secondary plate closure in rat

Developmental changes in cellular and extracellular structural macromolecules in the secondary palate and in the nasal cavity of the mouse

The aim of this study was to analyse the hitherto largely unknown expression patterns of some specific cellular and extracellular molecules during palate and nasal cavity development. We showed that epithelia of the developing palate and the vomerine epithelium express similar sets of structural proteins. With the exception of keratin 15, which becomes barely detectable in the elevated palatal shelves, nearly all of these proteins become upregulated at the presumptive areas of fusion and in the adhering epithelia of the palate and nasal septum. In vivo and in vitro analyses indicated that reduction in the amount of keratin 15 protein is independent of Tgfbeta-Alk5 signalling. Foxa1 expression also highlighted the regionalization of the palatal and nasal epithelia. Owing to the lack of reliable markers of the palatal periderm, the fate of peridermal cells has been controversial. We identified LewisX/stage-specific embryonic antigen-1 as a specific peridermal marker, and showed that numerous peridermal cells remain trapped in the medial epithelial seam (MES). The fate of these cells is probably apoptosis together with the rest of the MES cells, as we provided strong evidence for this event. Heparan sulphate, chondroitin-6-sulphate, and versican displayed dynamically changing distribution patterns. The hitherto-unknown innervation pattern of the developing palate was revealed. These findings may be of value for unravelling the pathogenesis of palatal clefting.

The effect of vitamin A on fusion of mouse palates. I. Retinyl palmitate and retinoic acid in vivo

C57B1 mice were given orally one, two , or three doses of ritinyl palmitate or retinoic acid on day 11, 12, 13, or 14 or pregnancy to determine 1) if it was possible to produce cleft palate at any time during palatal development of the mouse embryo, and 2) the maternal and fetal levels of vitamin A associated with the production of clefts. Whereas a single dose of either substance was sufficient to cause clefts on day 11 or day 12, three doses at 3-hour intervals were necessary to cause clefts on day 14. Most of these clefts were incomplete. Measurement of vitamin A levels in maternal serum and fetuses of dams after administration of retinyl palmitate or retinoic acid on day 11 and day 14 of pregnancy showed that transplacental passage of retinyl palmitate, retinol, and retinoic acid had taken place. Analysis of fetal serum on day 14 showed increase in levels of retinyl palmitate, retinol, and retinoic acid after dosing with retinyl palmitate, and in retinoic acid alone after dosing with retinoic acid. In both cases peak levels were observed within 3 hours. Our findings suggest that the effect of vitamin A on the developing mouse palate is direct, occurring soon after its administration, and that duration of exposure is as important as its concentration in vivo. The apparent change in sensitivity of mouse palate between day 11 and day 14 of pregnancy is discussed.