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Gross and cellular analysis of 6-mercaptopurine-induced cleft palate in hamster
1Department of Oral Biology, University of British Columbia, Vancouver, Canada.
Insights
6-mercaptopurine (6MP) causes cleft palate in hamster fetuses by stunting palatal shelf growth. Early cellular changes, including nuclear swelling and abnormal lysosomes, precede the breakdown of tissue structure, leading to failed palate fusion.
Area of Science:
- Developmental biology
- Teratology
- Cell biology
Background:
- Cleft palate is a common birth defect.
- 6-mercaptopurine (6MP) is an immunosuppressive drug known to cause developmental abnormalities.
- Understanding the precise mechanisms of drug-induced teratogenesis is crucial for prevention.
Purpose of the Study:
- To investigate the morphological, histochemical, and ultrastructural pathogenesis of 6-mercaptopurine (6MP)-induced cleft palate in hamster fetuses.
- To elucidate the cellular and molecular events leading to palate malformation following 6MP exposure.
Main Methods:
- Gross and light microscopy of hamster fetuses exposed to 6MP.
- Ultrastructural analysis of palatal tissues at various time points post-drug administration.
- Histochemical examination of cellular changes.
Main Results:
- 6MP administration stunted vertical palatal shelf growth, resulting in cleft palate.
- Early ultrastructural alterations in mesenchymal cells included nuclear membrane swelling and abnormal lysosome formation.
- Breakdown of the basal lamina and epithelial-mesenchymal contacts occurred later, hindering palate fusion.
Conclusions:
- 6MP interferes with cytodifferentiation during early palatal development.
- The observed cellular changes, particularly lysosome appearance, represent a sublethal response to 6MP.
- These disruptions ultimately lead to the induction of cleft palate in developing hamster fetuses.
Abstract:
The present study analyzes the morphological, histochemical, and ultrastructural aspects of the pathogenesis of 6-mercaptopurine (6MP)-induced cleft palate in hamster fetuses. Gross and light microscopic observations indicated that 6MP stunts the growth of vertical palatal shelves and thus induces cleft palate. Ultrastructural analysis showed that, in contrast to controls, 6MP-induced alterations were first seen in the mesenchymal cells 24 hr after drug administration. The initial alterations were characterized by swelling of the nuclear membrane. During the next 12 hr, lysosomes were seen first in the mesenchymal cells and then in the cells of the medial edge epithelium (MEE) of the developing palatal primordia. The appearance of lysosomes was temporally abnormal and was interpreted as a sublethal response to 6MP treatment. Subsequently, the nuclear alterations and the lysosomes diminished; and 48 hr after 6MP administration, they were absent from the palatal tissues. Ninety hours after 6MP administration, unlike the controls (in which the palatal shelves were already fused), changes were seen at the epithelial-mesenchymal interface in the developing cleft palatal shelves. These changes were characterized by breakdown of the basal lamina and epithelial-mesenchymal contacts. Eventually, at term, the MEE of the vertical shelf stratified. It was suggested that 6MP affected cytodifferentiation in the palatal tissues during the critical phase of early vertical shelf development and thereby induced cleft palate.