Cloning and expression of the chicken immunoglobulin joining (J)-chain cDNA

The J chain is a component of polymeric immunoglobulin (Ig) molecules and m ay play an important role in their polymerization and the transport of poly meric Ig across epithelial cells. In this study, the primary structure of t he chicken J chain was determined by sequencing cDNA clones. The cDNA had a n open reading frame of 476 nucleotides encoding a putative protein of 158 amino acid residues including the signal sequence. The 3' untranslated regi on consisted of 1216 nucleotides and a poly(A) tail. The deduced amino acid sequence of the chicken J chain had a high degree of homology to that of h uman, cow, rabbit, mouse, frog, and earthworm, with eight conserved Cys res idues identical to the mammalian J chains. Northern blot hybridization perf ormed with total RNA from various chicken tissues revealed high levels of J -chain mRNA expression in spleen, intestine, Harderian gland, and bursa of Fabricius, and low levels in the thymus. The J chain was expressed in the b ursa as early as day 15 of embryogenesis. These data indicated that the chi cken J-chain gene displays a high degree of homology with that of other spe cies, and is expressed at an early stage of development of the chicken immu ne system.