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Impaired development of the thymic primordium after neural crest ablation
1Department of Anatomy, Medical College of Georgia, Augusta 30912-2000.
Insights
Neural crest ablation early in development inhibits the formation of epithelial thymic primordia. This suggests cranial neural crest mesenchyme is essential for initiating thymus development and supporting lymphoid stem cell differentiation.
Area of Science:
- Developmental biology
- Immunology
- Embryology
Background:
- Impaired thymic development is observed late in development following neural crest ablation.
- Early developmental changes in the thymus due to neural crest ablation remain unclear.
Purpose of the Study:
- To investigate the early effects of neural crest ablation on thymus development in chick embryos.
- To determine the role of cranial neural crest in initiating and sustaining thymic organogenesis.
Main Methods:
- Studied epithelial primordia of the thymus in chick embryos on day six of incubation.
- Compared neural crest-ablated embryos with sham-operated and untreated controls.
- Transplanted thymic primordia from experimental and control embryos to chorioallantoic membranes.
Main Results:
- Neural crest ablation significantly inhibited the formation of epithelial thymic primordia, resulting in fewer and smaller structures.
- Transplanted primordia from control embryos developed into typical embryonic thymus organs.
- Transplanted primordia from ablated embryos showed limited development, forming small epithelial structures with poor lymphoid development.
Conclusions:
- Mesenchyme derived from cranial neural crest is critical for initiating epithelial structures from pharyngeal pouches.
- This mesenchyme is essential for attracting and supporting lymphoid stem cell proliferation and differentiation, thus sustaining thymus development.
Abstract:
Impaired thymic development as a result of ablation of neural crest has been observed in embryos late in development. The present study was initiated to determine what changes are effected early in thymic development by neural crest ablation. The epithelial primordia of the thymus were studied in chick embryos on the sixth day of incubation. Embryos with neural crest ablations were compared with sham-operated and untreated controls. Neural crest ablation inhibited formation of epithelial thymic primordia. Primordia in experimental embryos were fewer in number and were smaller than in shams and untreated controls. When primordia from shams and controls were transplanted to the chorioallantoic membrane of chick hosts, they were able to develop into organs with the typical features of embryonic thymus. Similar transplantation from neural crest-ablated animals, on the other hand, led to small, predominantly epithelial structures with meager lymphoid development. These findings are consistent with the hypothesis that mesenchyme derived from cranial neural crest is critical in initiating and sustaining the development from pharyngeal pouches of epithelial structures competent to attract and support the proliferation and differentiation of lymphoid stem cells.