Thymocyte clones from 14-day mouse embryos II. Transcription of T3γ gene may precede rearrangement of TcRδ and expression of T3δ, T3ɛ and T11 genes

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Abstract
We have studied the state of TcRδ gene and the expression of T3δ, T3ε, T3γ and T11 (CD2) genes in the fetal thymocyte (FT) clones A2, G15, H5, E10, D5, H12, F1 and D11 obtained from a 14‐day B10.BR mouse fetal thymus. The eight FT clones contain the TcRδ gene in the germ‐line configuration as determined by Southern blot analysis. With the exception of clones E10 and D5, the other six FT clones express normal sized transcripts for T3δ gene and none of the eight FT clones produced detectable RNA transcripts for T3δ, T3ε and T11 genes as assessed by Northern blot analysis. Together with our previous work showing that all eight FT clones contain the TcRδ and the TcRβ gene clusters in the germ‐line configuration, the data indicate that the FT clones represent the earliest stage of T cell development identified within the thymus. Our results provide evidence that (a) the T3γ gene is the first of the genes that encode components of a TcR/T3 complex to be expressed in ontogeny within the thymus; (b) the T3 (δ, E, γ) genes are switched on asynchronously and their expression must be differentially regulated, and (c) the T11 gene product may not be involved in early stages of T cell development within the thymus.