The joining (J) chain is present in invertebrates that do not express immunoglobulins.
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 extent invertebrates and vertebrates.
Takahashi
T
T
Department of Pathology, School of Dentistry, Nihon University, Tokyo, Japan.
Iwase
T
T
Takenouchi
N
N
Saito
M
M
Kobayashi
K
K
Moldoveanu
Z
Z
Mestecky
J
J
Moro
I
I
D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000737:chemistry; D015870:Gene Expression; D005803:Genes, Immunoglobulin; D006651:Histocytochemistry; D006801:Humans; D007144:Immunoglobulin J-Chains / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D008974:Mollusca / Q000235:genetics; D009835:Oligochaeta / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
D017931:DNA Primers; D007144:Immunoglobulin J-Chains; D012333:RNA, Messenger