Genomic analysis of immunity in a Urochordate and the emergence of the vertebrate immune system: "waiting for Godot".
Genome-wide sequence analysis in the invertebrate chordate, Ciona intestinalis, has provided a comprehensive picture of immune-related genes in an organism that occupies a key phylogenetic position in vertebrate evolution. The pivotal genes for adaptive immunity, such as the major histocompatibility complex (MHC) class I and II genes, T-cell receptors, or dimeric immunoglobulin molecules, have not been identified in the Ciona genome. Many genes involved in innate immunity have been identified, including complement components, Toll-like receptors, and the genes involved in intracellular signal transduction of immune responses, and show both expansion and unexpected diversity in comparison with the vertebrates. In addition, a number of genes were identified which predicted integral membrane proteins with extracellular C-type lectin or immunoglobulin domains and intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIMs) and immunoreceptor tyrosine-based activation motifs (ITAMs) (plus their associated signal transduction molecules), suggesting that activating and inhibitory receptors have an MHC-independent function and an early evolutionary origin. A crucial component of vertebrate adaptive immunity is somatic diversification, and the recombination activating genes (RAG) and activation-induced cytidine deaminase (AID) genes responsible for the Generation of diversity are not present in Ciona. However, there are key V regions, the essential feature of an immunoglobulin superfamily VC1-like core, and possible proto-MHC regions scattered throughout the genome waiting for Godot.
Azumi
Kaoru
K
Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
De Santis
Rosaria
R
De Tomaso
Anthony
A
Rigoutsos
Isidore
I
Yoshizaki
Fumiko
F
Pinto
Maria Rosaria
MR
Marino
Rita
R
Shida
Kazuhito
K
Ikeda
Makoto
M
Ikeda
Masami
M
Arai
Masafumi
M
Inoue
Yasuhito
Y
Shimizu
Toshio
T
Satoh
Nori
N
Rokhsar
Daniel S
DS
Du Pasquier
Louis
L
Kasahara
Masanori
M
Satake
Masanobu
M
Nonaka
Masaru
M
D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D002938:Ciona intestinalis / Q000235:genetics* / Q000276:immunology*; D016207:Cytokines / Q000502:physiology; D005805:Genes, MHC Class I / Q000502:physiology; D005802:Genes, MHC Class II / Q000502:physiology; D016678:Genome; D007113:Immunity, Innate / Q000235:genetics; D008562:Membrane Glycoproteins / Q000502:physiology; D010587:Phagocytosis; D011956:Receptors, Cell Surface / Q000502:physiology; D015398:Signal Transduction; D051193:Toll-Like Receptors
D016207:Cytokines; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D051193:Toll-Like Receptors