Molecular and functional in vivo characterisation of murine Dectin-1 isoforms

Dectin-1 is a C-type lectin-receptor involved in sensing fungi by innate immune cells. Encoded by the Clec7a gene, Dectin-1 exists in two major splice isoforms, Dectin-1a and 1b, which differ in the presence of a membrane-proximal stalk domain. As reported previously, this domain determines degradative routes for Dectin-1a and 1b leading to the generation of a stable N-terminal fragment exclusively from Dectin-1a. Here, we narrow down the responsible part of the stalk and demonstrate the stabilisation of the Dectin-1a N-terminal fragment in tetraspanin-enriched microdomains. C57BL/6 and BALB/c mice show divergent Dectin-1 isoform expression patterns, which are caused by a single nucleotide polymorphism in exon 3 of the Clec7a gene, leading to a non-sense Dectin-1a mRNA in C57BL/6 mice. Using backcrossing, we generated mice with the C57BL/6 Clec7a allele on a BALB/c background and compared these to the parental strains. Expression of the C57BL/6 allele leads to the exclusive presence of the Dectin-1b protein. Furthermore, it was associated with higher Dectin-1 mRNA expression, but less Dectin-1 at the cell surface according to flow cytometry. In neutrophils, this altered ROS production induced by Dectin-1 model ligands, while cellular responses in macrophages and dendritic cells were not significantly influenced by the Dectin-1 isoform pattern.