Single nucleotide polymorphisms in mannan-binding lectins and ficolins in various strains of mice

Mannan-binding lectin (MBL) and ficolin are collagenous lectins produced primarily by the liver and are involved in innate resistance to microbial pathogens. Mice have two MBL genes (Mbl1 and Mbl2) that encode MBL-A and MBL-C, respectively. Similarly, the murine Fcna and Fcnb genes encode ficolin-A and ficolin-B. Several single nucleotide polymorphisms (SNP) in the human MBL2 gene are responsible for various innate immune dysfunctions due to abnormal structure or expression of human MBL-C. In these studies, we identified SNPs in the expressed collagenous lectin genes Mbl1, Mbl2, Fcna, and Fcnb in 10 strains of mice designated high priority Group A strains by the Mouse Phenome Project (129S1/SvImJ, A/J, BALB/cByJ, C3H/HeJ, C57BL/6 J, DBA/2 J, FVB/NJ, SJL/J, CAST/EiJ and SPRET/EiJ) by sequencing gene exons by reverse transcription-polymerase chain reaction (RT-PCR). Sequence comparisons identified a total of 15 structural SNPs in Mbl1 in two strains, 27 SNPs in Mbl2 in five strains, and 19 and 15 SNPs in Fcna and Fcnb, respectively, in two strains. Two non-synonymous SNPs were identified in the collagen-like domain of mouse Fcnb that are similar to the coding polymorphisms in the collagen-like domain of human MBL2. Most of the non-synonymous SNPs identified in Mbl1 and Mbl2 occurred in the carbohydrate-recognition domains (CRDs), and some resulted in altered residues close to known ligand binding sites. Similarly, most non-synonymous SNPs of Fcna and Fcnb were identified in the fibrinogen-like CRD. The miscoding SNPs found in the CRD regions of mouse Mbl1, Mbl2, Fcna and Fcnb may be associated with strain differences in glycan binding avidity and disposition of microbial or host ligands. Furthermore, the non-synonymous mutations in the collagen-like domain of Fcnb may alter the structure of the mature ficolin-B protein leading to functional deficiencies. These differences may be important in the pathogenesis of susceptibility differences between inbred strains to various infectious microorganisms.