A novel BTK-like protein involved in immune response in Lethenteron japonicum.

Bruton's tyrosine kinase (BTK) plays an important role in the development, differentiation and signal transduction of B-lymphocyte. Lymphocyte-like cells and unique variable lymphocyte receptors have been found in the Japanese lamprey Lethenteron japonicum, an agnatha known to be lacking T or B lymphocyte, and the oldest agantha in existence. In this study a BTK-like gene from L. japonicum was identified and characterized. It contained a 1992-bp open reading frame (ORF), a 157-bp 5'-untranslated region (UTR) and a 567-bp 3'-UTR. Phylogenetic analysis indicated it had high sequence homology with BTKs from other vertebrates. Real-time PCR analysis showed that the transcript of the L. japonicum BTK-like gene was distributed in various immune associated tissues, and the level of which was upregulated in leukocytes after the animal was stimulated with LPS. This observation was further confirmed by FACS and western blot analyses. These results indicated that the BTK-like gene identified in L. japonicum may play an important role in the immune response of lamprey.