Differentiation of epithelial cells in the mouse thymus

Summary The foetal and post-natal development of the mouse thymus was studied with the electron microscope paying particular attention to the differentiation of the epithelial cells. At about 13 days' gestation, the thymus was composed principally of undifferentiated epithelial cells and some lymphoblasts. The latter accumulated rapidly but did not show much evidence of mitotic activity until after the development of differentiated cortical epithelial cells which appeared during the 15th day of gestation. Further differentiation of epithelial cells did not occur until near term when medullary cystic epithelial cells appeared, and post-natally when small Hassall's corpuscles were developed. Undifferentiated and dividing epithelial cells were seen in the medulla and were present in all postnatal animals examined.This is publication number 1400 from the Walter & Eliza Hall Institute of Medical Research.The author is grateful to Prof. G. J. V. Nossal, Dr. J. F. A. P. Miller and Dr. P. J. Russell for their interest and assistance with various aspects of this study. Special thanks are due to Miss Mary Bravington for her skilled technical assistance. This investigation was supported by grants from the Jane Coffin Childs Memorial Fund for Medical Research and the National Health and Medical Research Council of Australia. The Electron Microscope Laboratory was equipped and supported by grants from the Australian Research Grants Committee, J. B. Were and Sons and the Potter Foundation.