The genes encoding bovine SP-A, SP-D, MBL-A, conglutinin, CL-43 and CL-46 form a distinct collectin locus on Bos taurus chromosome 28 (BTA28) at position q.1.8-1.9

Collectins are a group of C-type lectins involved in the innate immune system, where they mediate and modulate clearance of pathogens. The health status of cattle is of major economical and ethical concern; therefore, the study of bovine collectins is of importance. The collectins conglutinin, CL-43 and CL-46 are only present in Bovidae and the characterization of their genes indicates that they are structural descendants of another collectin, lung surfactant protein D (SP-D). In this study, we assembled BAC clones into a contig spanning 330-1150 kb, which includes the bovine genes encoding the collectins SP-A (SFTPA), SP-D (SFTPD), mannan-binding lectin A (MBL1), CL-43 (COLEC9), CL-46 (COLEC13) and conglutinin (COLEC8). In the same contig, we also identified a gene that potentially encodes a novel conglutinin-like collectin (COLEC14). The arrangement of STFPA, SFTPD and MBL1 is homologous to the organization found in humans and mice, whereas the Bovidae-specific collectin genes, COLEC8, COLEC9 and COLEC13, extend from SFTPD. Proximal to the collectin locus at BTA28q1.8-1.9, and included in the contig, we found the microsatellite IDVGA8, which may be a valuable marker for tracking polymorphisms in the linked collectin genes.     

CL-46, a novel collectin highly expressed in bovine thymus and liver

Collectins are oligomeric molecules with C-type lectin domains attached to collagen-like regions via alpha-helical neck regions. They bind nonself glycoconjugates on the surface of microorganisms and inhibit infection by direct neutralization, agglutination, or opsonization. During the characterization of the gene encoding bovine CL-43 (43-kDa collectin), we identified a novel collectin-gene. We report the cloning and partial characterization of the novel collectin CL-46. The mRNA comprises 1188 nucleotides encoding a protein of 371 aa with an included leader peptide of 20 residues. CL-46 has two cysteine residues in the N-terminal segment, a potential N-glycosylation site in the collagen region, and an extended hydrophilic loop close to the binding site of the carbohydrate recognition domain. It is expressed in the thymus, liver, mammary gland, and tissues of the digestive system. Recombinant CL-46 corresponding to the alpha-helical neck region and the C-type lectin domain binds preferential N-acetyl-D-glucoseamine and N-acetyl-D-mannoseamine. The gene encoding CL-46 spans approximately 10 kb and consists of eight exons, with high structural resemblance to the gene encoding human surfactant protein D. It is located on the bovine chromosome 28 at position q1.8 together with the gene encoding conglutinin and CL-43. Several potential thymus-related cis-regulatory elements were identified in the 5'-upstream sequence, indicating that the expression in thymus may be modulated by signals involved in T cell development.