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Lack of Delta like 1 and 4 expressions in nude thymus anlages

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Abstract

Notch signaling is required for the early steps in T cell development. However, distribution of Notch ligands in the thymus anlages is not clear. We investigated the expressions of Delta like (Dll) 1 and Dll4 in the mouse thymus anlages. In the normal thymus anlages on embryonic day 13, Dll4 is strongly expressed throughout the epithelial region, but Dll1 is expressed only in scattered cells. In contrast, epithelial cells of the nude thymus anlages express neither Dll1 nor Dll4. These results indicate that expressions of Dll1 and Dll4 in thymic epithelial cells are regulated by Foxn1 transcriptional factor.

Introduction

Notch signaling is required for the early steps in T cell development [1], [2]. Hematopoietic progenitor cells to T, NK, and/or DC lineages [3] immigrate to the mesenchymal layer of the thymus anlages as early as embryonic day (Ed) 11 through surrounding connective tissues [3], [4]. Early immigrant progenitor cells obtain Notch signaling from embryonic thymic epithelial cells when they enter the epithelial region on Ed12 [5]. Progenitor cells broadly distribute among epithelial regions of the thymus anlages, and begin to proliferate through interaction with epithelial cells on Ed12 [4]. Then, many of those progenitor cells differentiate to CD25 positive cells on Ed13 [6]. Expression of Notch ligands, Jagged 1, 2, Delta like (Dll) 1, 3, and 4 in the fetal thymus anlages has been shown by RT-PCR [5], [7], [8], [9], however, Dll3 is only weakly expressed in the fetal thymus [5], [9]. The bone marrow stromal cell line S17 cells expressing human Jagged 1 do not induce differentiation of T cells from progenitor cells [10]. In Jagged 2 mutant mice, normal development of αβT cells is seen [11]. It is clearly demonstrated that Notch signaling by Dll1 [7] or Dll4 [8] drives T lymphopoiesis in vitro. However, distribution of Notch ligands, Dll1 and Dll4, in the thymus anlages has not been clarified yet. On the other hand, defects in epithelial cell development in nude mice, which have a point mutation in Foxn1 gene [12], have been shown by several authors [4], [13]. Since Foxn1 gene codes a transcription factor for epithelial cell development, it is important to address the question of whether expressions of Dll1 and Dll4 are regulated under the Foxn1 transcription factor. In the present study, we showed that Dll1 and Dll4 are expressed in the normal thymus anlage, but not in the nu/nu thymus anlage.

Section snippets

Mice

KSN nu/nu (nu/nu) and (DDD × KSN)F1nu/+ (nu/+) mouse embryos were obtained by mating of KSN nu/nu female with KSN nu/nu male mice, and DDD female mice, which are parental strain of KSN mice, and KSN nu/nu male mice, respectively. Mice were mated at night and the females were examined for vaginal plugs the following morning. The day on which a vaginal plug was found was designated as Ed 0.

Immunohistochemistry and in situ hybridization

Embryos were embedded in OCT compound and snap-frozen in liquid nitrogen. They were cut into serial sections 5 

Results and discussion

To investigate whether Dll1 and Dll4 mRNAs are expressed in the mouse thymus anlages, in situ hybridization analysis of whole embryonic sections of nu/+ mice was performed (Figs. 1A–H). At Ed12, Dll1 expression was only detected in a few cells of the epithelial region of the thymus anlages of one in 6 nu/+ embryos (Figs. 1A and B). At Ed13, Dll1 expression was observed in some scattered cells among the whole epithelial region of the thymus anlages of all nu/+ embryos examined (Figs. 1E and F).

Acknowledgments

We thank Dr. Shigeru Chiba (University of Tokyo) for providing the plasmids containing Dll1 cDNA, Dr. Katsuto Hozumi (Tokai University) for discussion. This work was supported by the grant from the Ministry of Education, Culture, Sports, Sciences and Technology, Japan.

References (20)

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