Molecular characterization, tissue expression, and mapping of a novel Siglec-like gene (SLG2) with three splice variants.

The sialic acid binding immunglobulin-like lectin (Siglec) family is a recently described member of the immunoglobulin superfamily. Within the Siglec family, there exists a subgroup, which bears a high degree of homology with the molecule CD33 (Siglec-3), and has thus been designated the CD33-like subgroup of Siglecs. Members of this subgroup have been localized to chromosome 19q13.4. Through the positional candidate approach, we identified a novel potential member of this subgroup of Siglecs. We have characterized the complete genomic structure of this gene, determined its chromosomal localization, its homology to other members of the Siglec family, and its tissue expression profile. This new Siglec-like gene is comprised of 11 exons, with 10 intervening introns, and is localized 278 kb telomeric to Siglec-9 and 35 kb centromeric to Siglec-8 and on chromosome 19q13.4. The coding region consists of 2094 base pairs, and encodes for a putative 76.6 kDa protein. All Siglec-conserved structural features, including V-set domain, three C-set domains, transmembrane domain, ITIM and SLAM motifs, were found in this Siglec-like gene. Also, it has the conserved amino acids essential for sialic acid binding. The Siglec-like gene has 40-66% homology with members of the CD33-like subgroup, including Siglecs 5-9. Through RT-PCR we have examined the expression profile of this new gene in a panel of human tissues and found it to be primarily expressed in the bone marrow, spleen, brain, small intestine, colon, and spinal cord. We were also able to identify three different splice variants of the new gene. This gene may represent the latest novel member of the CD33-like subgroup of Siglecs, and, given its high degree of homology, it may also serve a regulatory role in the proliferation and survival of a particular hematopoietic stem cell lineage, as has been found for CD33 and Siglec-7.