Early development of the thymus in Xenopus laevis

Authors

  • Young-Hoon Lee,

    1. Department of Oral Anatomy, School of Dentistry and Institute of Oral Biosciences, Chonbuk National University, Jeonju, Republic of Korea
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    • Young-Hoon Lee and Allison Williams contributed equally to this work.

  • Allison Williams,

    1. Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
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    • Young-Hoon Lee and Allison Williams contributed equally to this work.

  • Chang-Soo Hong,

    1. Department of Biological Sciences, College of Natural Sciences, Daegu University, Gyeongsan, Republic of Korea
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  • Youngjae You,

    1. Department of Oral Anatomy, School of Dentistry and Institute of Oral Biosciences, Chonbuk National University, Jeonju, Republic of Korea
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  • Makoto Senoo,

    1. Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
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  • Jean-Pierre Saint-Jeannet

    Corresponding author
    1. Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
    2. Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York
    • Department of Oral Anatomy, School of Dentistry and Institute of Oral Biosciences, Chonbuk National University, Jeonju, Republic of Korea
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Correspondence to: Jean-Pierre Saint-Jeannet, New York University, College of Dentistry. Department of Basic Science & Craniofacial Biology, 345 East 24th Street, New York, NY 10010. E-mail: jsj4@nyu.edu

Abstract

Background: Although 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. 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. Results: In most species Hoxa3 is expressed in the third pharyngeal pouch endoderm where it directs thymus formation. 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. 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. 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. Conclusions: These studies provide novel information on early thymus development in Xenopus, and highlight a number of features that distinguish Xenopus from other organisms. Developmental Dynamics, 2012. © 2012 Wiley Periodicals, Inc.

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