The Joining (J) Chain is Present in Invertebrates that do not Express Immunoglobulins

• Published in: Proceedings of the National Academy of Sciences - PNAS 1996-03, Vol.93 (5), p.1886-1891
• Main Authors: Takahashi, Tomihisa, Iwase, Takashi, Takenouchi, Nobuko, Saito, Manabu, Kobayashi, Kunihiko, Moldoveanu, Zina, Mestecky, Jiri, Moro, Itaru
• Format: Article
• Language: English
• Subjects: Animals; Base Sequence; Cell lines; Complementary DNA; DNA; DNA Primers - chemistry; Earthworms; Epithelial cells; Gene Expression; Genes; Genes, Immunoglobulin; Histocytochemistry; Humans; Immunity (Disease); Immunoglobulin J-Chains - chemistry; Immunoglobulin J-Chains - genetics; Immunoglobulin J-Chains - metabolism; Invertebrates; Molecular Sequence Data; Molecular Weight; Mollusca - genetics; Oligochaeta - genetics; Polymerase chain reaction; Proteins; Reverse transcriptase polymerase chain reaction; Ribonucleic acid; RNA; RNA, Messenger - genetics; Sequence Alignment; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid; Slugs; Vertebrates
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.5.1886

Joining (J) chain is a component of polymeric, but not monomeric, immunoglobulin (Ig) molecules and may play a role in their polymerization and transport across epithelial cells. To date, study of the J chain has been confined to vertebrates that produce Ig and in which the J chain displays a considerable degree of structural homology. The role of the J chain in Ig polymerization has been questioned and, since the J chain can be expressed in lymphoid cells that do not produce Ig, it is possible that the J chain may have other functions. To explore this possibility, we have surveyed J-chain gene, mRNA, and protein expression by using reverse transcriptase-coupled PCR, Northern blot analysis, and immunoblot analysis in invertebrate species that do not produce Ig. We report that the J-chain gene is expressed in invertebrates (Mollusca, Annelida, Arthropoda, Echinodermata, and Holothuroidea), as well as in representative vertebrates (Mammalia, Teleostei, Amphibia). Furthermore, J-chain cDNA from the earthworm has a high degree of homology (68-76%) to human, mouse, and bovine J chains. Immunohistochemical studies reveal that the J chain is localized in the mucous cells of body surfaces, intestinal epithelial cells, and macrophage-like cells of the earthworm and slug. This study suggests that the J chain is a primitive polypeptide that arose before the evolution of Ig molecules and remains highly conserved in extant invertebrates and vertebrates.