Abstract
The mammalian JAM family is composed of three cell surface receptors. Interactions between the proteins have well-characterised roles in inflammation and tight junction formation, but little is known about their function in early development. Recently, we identified a role for jamb and jamc in zebrafish myocyte fusion. Genome duplication in the teleost lineage raised the possibility that additional JAM family paralogues may also function in muscle development. To address this, we searched the zebrafish genome to identify potential paralogues and confirmed their homology, bringing the total number of zebrafish jam family members to six. We then compared the physical binding properties of each paralogue by surface plasmon resonance and determined the gene expression patterns of all zebrafish jam genes at different stages of development. Our results suggest a significant sub-functionalisation of JAM-B and JAM-C orthologues with respect to binding strength (but not specificity) and gene expression. The paralogous genes, jamb2 and jamc2, were not detected in the somites or myotome of wild-type embryos. We conclude that it is unlikely that the paralogues have a function in primary myogenesis.
Highlights
The JAM (Junctional adhesion molecule) family is a small, deuterostome lineage-restricted subgroup of the immunoglobulin superfamily [1]
Four zebrafish JAM family orthologues, F11r, Jam2a, Jam2b and Jam3b, were included in recent AVEXIS screens for cell surface protein interactions that are important for zebrafish development [52,53,54]
Alignments of the ectodomains of zebrafish and mammalian JAM family proteins showed conservation of key features (Figure S1) such as the putative binding motif in the distal immunoglobulin superfamily (IgSF) domain (R-V/I/L-E; [7,8]), or in the case of JAM-B and JAM-C orthologues, the non-canonical disulphide bond between A and G b-strands in the proximal IgSF domain
Summary
The JAM (Junctional adhesion molecule) family is a small, deuterostome lineage-restricted subgroup of the immunoglobulin superfamily [1]. Many other roles have been proposed for each member of the family, including: angiogenesis [17,18,19,20], cancer [9,19,21,22,23], spermatid development and motility [24,25,26], and the maintenance of the myelin sheath formed by Schwann cells [27] These diverse processes are most likely unified by an important function of the JAM proteins – the formation and maintenance of adhesion and tight junctions between cells [12,13,28,29,30,31,32,33,34,35]
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