Vertical development of the secondary palate in hamster embryos following exposure to 6‐mercaptopurine

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Abstract
Cellular aspects of vertical development of the secondary palate were examined in control and 6-mercaptopurine (6MP)-treated hamster embryos. Cross-sectional area of the palatal shelf was measured and the numbers of both epithelial and mesenchymal cells counted. Also, in 6MP-treated palates the damaged mesenchymal cells, characterized by the presence of dense bodies, were counted. DNA synthesis in both control and treated fetuses was measured by 3H-thymidine incorporation. The results indicated that both the shelf area and cell numbers increased with age in control and 6MP-treated palates. However, in controls the mesenchymal cell density and DNA synthesis showed two peaks that were absent following 6MP treatment. Unlike controls, in treated embryos the damage to mesenchymal cells became increasingly pronounced between days 10:00 and 10:12 but subsided by day 11:00 of gestation. It is suggested that a major force in the development of the initial primordia and early vertical development of the palatal shelf may be provided by a spurt of DNA synthesis in the mesenchymal cells resulting in their increased number. After 6MP treatment, depression of DNA synthesis and consequent reduction in the mesenchymal cell number and density followed by cell damage lead to retardation in the vertical development of the palatal shelves.