Sequencing and expression of the CD3 gamma/delta mRNA in Pleurodeles waltl (urodele amphibian)

The CD3 complex is an essential component of the T-cell receptor (TCR) implicated in T-cell maturation and activation. This TCR has been identified in both cartilaginous and bony vertebrates. In different studies where the CD3 chains were cloned and sequenced, it appeared that the CD3 complex is composed of several chains, all susceptible to phosphorylation and able to transduce signals. Here, by an approach combining degenerative oligonucleotide primers and RACE-PCR, we report the cloning and sequencing of a CD3 cDNA from the salamander Pleurodeles waltl, highly homologous to the Xenopus and chicken CD3 gamma/delta cDNAs. Using semi-quantitative PCR and Northern blot analysis, we found the highest CD3 gamma/delta mRNA expression in the thymus; weaker expression was observed in the spleen and blood, followed by the intestine, therefore confirming the tissue and lymphoid specificities of this mRNA. The signals in the spleen, blood and intestine represented 55%, 33% and 16%, respectively, of the signal detected in the thymus. During the embryonic and larval stages of Pleurodeles waltl development, CD3 gamma/delta mRNA expression begins early at the neurula stage (stage 15, 69 h after laying), increases up to stage 33 (9 days after laying) and afterwards remains stable, at least until the larval stage 42 (28 days after laying). As the thymus primordium appears much later, the question of the formation and maturation of the first T-cell precursors outside this organ is posed.