Transverse sections, dorsal towards the top. I,J are a higher magnification view of G,H. K,L: Expression of p63, an epithelial stem cell factor. H: Hematoxylin and eosin staining of the same section. G: At stage 50, the thymus primordia have increased in size but retained their dorsolateral position (arrows). Longitudinal section of a stage-47 tadpole, anterior towards the top. F: Higher magnification view of the right thymic primordium shown in E. The thymus primordia (arrows) are located lateral and ventral to the hindbrain (hb), between the eye and the developing inner ear (ie), as seen on a longitudinal section (D). C: Transverse section of a stage-47 tadpole, at the level of the pharynx (ph) dorsal towards the top. A: The thymus primordia are recognizable at around stage 47 (arrows). These studies provide novel information on early thymus development in Xenopus, and highlight a number of features that distinguish Xenopus from other organisms.įig. Using transplantation experiments we show that while neural crest cells populate the thymus primordia, they are not required for the specification and initial development of this organ or for T-cell differentiation in frogs. Unlike other species foxn1 is not detected in the epithelium of the pharyngeal pouch in Xenopus, rather, its expression is initiated as thymic epithelial cell starts to differentiate and express MHC class II molecules. In Xenopus, the thymus primordium is derived from the second pharyngeal pouch endoderm, which is hoxa3-negative, suggesting that a different mechanism regulates thymus formation in frogs. In most species Hoxa3 is expressed in the third pharyngeal pouch endoderm where it directs thymus formation. Here we examined the expression of three transcription factors that have been functionally associated with pharyngeal gland development, gcm2, hoxa3, and foxn1, and evaluated the neural crest contribution to thymus development. tropicalis v9.1 (Nigerian) on JBrowseĪlthough Xenopus laevis has been a model of choice for comparative and developmental studies of the immune system, little is known about organogenesis of the thymus, a primary lymphoid organ in vertebrates.
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