Genomic and molecular characterization of bovine surfactant protein D (SP-D)

Collectins are a group of C-type lectins involved in the innate host defense against pathogens. They selectively recognize non-self glyco-conjugates on the surface of microorganisms and induce lysis, agglutination, and phagocytosis to eliminate invading microorganisms. With the perspective of being able to identify surfactant protein D (SP-D) polymorphisms associated with immune-compromised phenotypes in cattle, we have characterized the gene encoding bovine SP-D and its proximal promoter. Cloning and sequencing of the bSP-D gene, including the complete 5'-untranslated sequence, reveal that the gene comprises nine exons spanning approximately 10.5 kb with an organization resembling the bovine conglutinin gene. The gene localizes to the same locus as the conglutinin gene on Bos taurus chromosome 28 at position q1.8, which also includes the genes encoding CL-43 and CL-46. Several potential cis-regulatory elements, similar to elements known to regulate the transcription of human SP-D, were identified in the 5'-upstream sequence. RT-PCR analysis revealed that bovine SP-D is heavily expressed in the lung and the trachea, but also in segments of the gastrointestinal tract, the mammary glands and the salivary glands. By genotyping we assigned two potential polymorphisms leading to variations in the amino acid composition of the carbohydrate recognition domain (242 Glu/Val and 268 Ala/Gly).