The putative invertebrate adaptive immune protein Litopenaeus vannamei Dscam (LvDscam) is the first reported Dscam to lack a transmembrane domain and cytoplasmic tail.
It has recently been suggested that Dscam (Down syndrome cell adhesion molecule), a member of the immunoglobulin superfamily (IgSF), plays an essential role in the alternative adaptive immune system of invertebrates. Here, we isolated and characterized the first shrimp Dscam from Litopenaeus vannamei. The LvDscam protein had an extracellular domain but lacked the expected transmembrane domain and cytoplasmic tail, both of which are found in all other members of the Dscam family (and may also be found in other L. vannamei Dscams that have not yet been isolated). In nervous tissue, expression levels of LvDscam were unexpectedly low. Phylogenetic analysis suggests that LvDscam is far from the Dscams found in other invertebrates. Nevertheless, the domain architecture of the extracellular region of LvDscam is similar to other invertebrate Dscams, and it exhibits the typical configuration of 10 immunoglobulin (Ig) domains, 6 fibronectin type 3 domains (FNIII) and one cell attachment sequence (RGD). Cloning and characterization of a total of 62 cDNAs from hemocytes collected from WSSV-free, WSSV-persistent and WSSV-acute-infected shrimp revealed 23 alternative amino acid sequences in the N-terminal of Ig2, 30 in the N-terminal of Ig3 and 13 in the Ig7 domain. This implies that LvDscam can potentially encode at least 8970 unique isoforms. Further analysis suggested that the LvDscam Ig2 and Ig3 regions are more functionally important than Ig7 in the shrimp's specific immune response against WSSV. We discuss how this tail-less, soluble Dscam can still play an active role in alternative adaptive immune response even while its axonal guidance functionality may be impaired.
Chou
Pin-Hsiang
PH
Institute of Biotechnology, College of Bioscience and Biotechnology, National Cheng Kung University, Tainan 701, Taiwan.
Chang
Hao-Shuo
HS
Chen
I-Tung
IT
Lin
Han-You
HY
Chen
Yi-Min
YM
Yang
Huey-Lang
HL
Wang
K C Han-Ching
KC
D000220:Adaptation, Biological; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015815:Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009928:Organ Specificity; D033561:Penaeidae / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism / Q000821:virology; D010802:Phylogeny; D016415:Sequence Alignment; D046848:White spot syndrome virus 1 / Q000502:physiology
D015815:Cell Adhesion Molecules