Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

A LARGE NUMBER OF TRDV GENES CHARACTERIZE THE TRD LOCUS IN SHEEP

DEL FARO L., PAGLIARULO D., ANTONACCI R., VACCARELLI G., MASSARI S., CICCARESE S.

Dipartimento di Anatomia Patologica e di Genetica, Università di Bari, Via Amendola 165/A, 70126 Bari

T cell receptor, TRDV genes, sheep

The T cell receptor (TcR) expressed on mature T lymphocytes is a disulfide-linked heterodimer composed of alpha and beta or gamma and delta glycoprotein subunits. The proportion, among total T lymphocytes, of T cell expressing gamma/delta TcR is known to vary greatly from one species to another. In humans and mice gamma/delta T cells account for less than 3% of the peripheral T cell pool (“gamma/delta low” species) whereas in artiodactyls and chicken gamma/delta T cells account for close to one-half of the peripheral T cell pool (“gamma/delta high” species). In all species, functional TcR chains are generated as a result of rearrangements of Variable (V), Diversity (D) and Joining (J) gene segments for beta and delta chains and only V and J elements for alpha and gamma chains. After transcription, the V(D)J sequence is spliced to a Constant (C) region.

The genomic organization of the TRD locus, encoding for delta chain, is known in humans and mice. In both species the genetic elements (TRDV and TRDJ genes and one TRDC gene) are embedded between the TRAV genes and the TRAJ segments. The TRDV genes are interspersed among the TRAV genes. In particular, the human TRD locus presents eight TRDV family genes with only one member each, three TRDD and four TRDJ elements. In mice only two of the TRDD and TRDJ segments and about eight functional TRDV genes are known. As a consequence of the low number of TRVD elements, the repertoire of delta chain is limited and restricted in all lymphoid tissues.

The molecular cloning of cDNAs from gamma/delta T cells of different artiodactyl species has shown that the variable region of delta chain results from the preferential utilization of an expanded family (TRDV1), consisting of a large number of members with different sequences. To establish whether the expression of this very large number of delta chains depends on the presence of different TRDV1 elements in the TRD locus of these animals, we started the study of TRD locus organization in sheep.

To this purpose a genomic sheep (Altamurana breed) DNA library, constructed in lambda DASHII, was screened under low stringency condition with a 0.4 Kb EcoRI/ScaI fragment of a cDNA for delta chain corresponding to TRDV1.10 gene. Fifteen clones were recovered and further characterized by Southern blot analysis with TRDV1.10 probe. The fragments of the clones hybridized with the probe were subcloned and sequenced. The sequencing analysis has shown that the clones contain different TRDV1 family genes, highly homologous within the coding as well as in the promoter regions. This confirms that most TRDV genes in sheep exist as a large number of elements belonging to only one family gene, which could be correlated with the high frequency of gamma/delta T cells in this species.