Gene families

TCR 8 chain genes in mice and in humans are on the respective chromosomes 14. Like IgH and TCR|3 loci, TCR 8 chain loci include D gene segments. The organization of the heptamer-nonamer motifs is such that D8 segments may join to each other, and whereas Vs-D82-J8 is the most frequent rearrangement in murine fetal 78 cells, most 8 rearrangements in adult mice are V8-D81-D82-J8. Likewise, whereas early human fetal rearrangements join V8 to J8 via a single, J-proximal D (D83), rearrangements late in gestation include two or three D segments.

The sizes of the human and mouse 8 gene families are difficult to assess, because V8 gene segments are interspersed among V0 gene segments (Figure 1), and some V segments can be used as V8 or Va. For example, human V84, V85 and V86 have each been found rearranged to Da or Jā€ž, as a result of which they are referred to by the new nomenclature as ADV6, ADV21 and ADV17, respectively (ADV denoting variable gene segments for both the alpha and delta loci). In the mouse, &four murine V genes are transcribed as either V8 or Va mRNAs, and thus denoted ADV7S1, ADV7S2, ADV11SS5 and ADV17S2. Nonetheless, there are characteristic features of V segments commonly used in TCR S chains (see below). As a result, it has been possible to estimate that there are sl6 mouse Vs genes. Of these, six are highly homologous members of a single (DV7/ADV7) family, reducing to 11 the number of distinct mouse VB segments, compared to -eight distinct human V8 genes. Although V.ā€ž genes are highly diverged, it is possible to identify human/mouse counterparts, e.g. mouse V81 and human V82, that are more closely related to each other than they are to other Vs in the same species.

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