Four primordial immunoglobulin light chain isotypes, including λ and κ, identified in the most primitive living jawed vertebrates

Abstract

The discovery of a fourth immunoglobulin (Ig) light (L) chain isotype in sharks has revealed the origins and natural history of all vertebrate L chains. Phylogenetic comparisons have established orthology between this new shark L chain and the unique Xenopus L chain isotype r. More importantly, inclusion of this new L chain family in phylogenetic analyses showed that all vertebrate L chains can be categorized into four ancestral clans originating prior to the emergence of cartilaginous fish: one restricted to elasmobranchs (r-cart/type I), one found in all cold-blooded vertebrates (r/teleost type 2/elasmobranch type IV), one in all groups except bony fish (k/elasmobranch type II), and one in all groups except birds (j/elasmobranch type III/teleost type 1 and 3). All four of these primordial L chain isotypes (r, r-cart, k and j) have maintained separate V region identities since their emergence at least 450 million years ago, suggestive of an ancient physiological distinction of the L chains. We suggest that, based upon unique, discrete sizes of complementarity determining regions 1 and 2 and other features of the V region sequences, the different L chain isotypes arose to provide different functional conformations in the Ig binding site when they pair with heavy chains.

Preferential combination between the light and heavy chain isotypes of fish immunoglobulins

“…While in teleost, three major Ig isotypes (IgM, IgD, and IgT/IgZ) have been identified, among which IgT/IgZ is the last one discovered (Danilova et al, 2005;Hansen et al, 2005) and is characterized as an antibody that specialized in mucosal immune responses in the gut and skin (Xu et al, 2013;Zhang et al, 2010Zhang et al, , 2011. On the other side, two IgL isotypes, k and l, are expressed in mammals (Criscitiello and Flajnik, 2007). But in birds, only one IgL isotype is discovered, which is an evolutionary homolog to mammalian l (Lundqvist Abbreviations: Ab, antibody; BCR, B cell receptor; C domain, constant domain; CH, heavy chain constant domain; CL, light chain constant domain; DN, double negative; D segment, diversity segment; FACS, fluorescence-activated cell sorting; FBS, fetal bovine serum; J segment, joining segment; HKL, head kidney leukocyte; Ig, immunoglobulin; IgH, immunoglobulin heavy chain; IgL, immunoglobulin light chain; LC, liquid chromatography; MS, mass spectrometry; ORF, open reading frames; PBL, peripheral blood leukocyte; qPCR, quantitative real-time PCR; RAG, recombination-activing gene; RSS, recombination signal sequence; V domain, variable domain; VH, heavy chain variable domain; VL, light chain variable domain; V segment, variable segment.…”

“…The third IgL isotype, s, seems to be expressed only in the ectothermic vertebrates, including cartilaginous fish, teleosts, and amphibians (Edholm et al, 2011;Schwager et al, 1991). While the recently identified IgL isotype, s-cart, is unique to elasmobranches (Criscitiello and Flajnik, 2007). Therefore, all vertebrate IgLs are proposed to be grouped into four main ancestral branches: l, k, s, and s-cart (Criscitiello and Flajnik, 2007).…”

“…While the recently identified IgL isotype, s-cart, is unique to elasmobranches (Criscitiello and Flajnik, 2007). Therefore, all vertebrate IgLs are proposed to be grouped into four main ancestral branches: l, k, s, and s-cart (Criscitiello and Flajnik, 2007). Based on this nomenclature, the originally reported teleost IgL1 and IgL3 can be classified into IgLkG and IgLkF, respectively, and IgL2 into IgLs.…”

“…IgL gene configuration is classified as either "translocon" or "cluster" in genome and assembled by RAG-1 and RAG-2 through recognizing the recombination signal sequences (RSS) at the border of V and J segments (Criscitiello and Flajnik, 2007;Krangel, 2003;Mcblane et al, 1995). Mammalian IgL gene is organized as "translocon" arrangement, with multiple V and J segments arrayed upstream of C gene segments as (V n -J n -C n ) (Hieter et al, 1980;Hofker et al, 1989;Vasicek and Leder, 1990).…”

“…Mammalian IgL gene is organized as "translocon" arrangement, with multiple V and J segments arrayed upstream of C gene segments as (V n -J n -C n ) (Hieter et al, 1980;Hofker et al, 1989;Vasicek and Leder, 1990). Teleost and cartilaginous fish IgL genes exhibit a cluster-type organization as (V-J-C) n (Cannon et al, 2004;Criscitiello and Flajnik, 2007). Beyond this, more than one copy of IgLk loci are found in different chromosomes of some teleost species (Edholm et al, 2011;Hikima et al, 2011;Yasuike et al, 2010), which probably arose because of the teleost-specific whole-genome duplication.…”