Cloning and Characterization of a Novel Mouse Siglec, mSiglec-F

Abstract

A novel mouse Siglec (mSiglec-F) belonging to the subfamily of Siglec-3-related Siglecs has been cloned and characterized. Unlike most human Siglec-3 (hSiglec-3)-related Siglecs with promiscuous linkage specificity, mSiglec-F shows a strong preference for ␣2-3-linked sialic acids. It is predominantly expressed in immature cells of the myelomonocytic lineage and in a subset of CD11b (Mac-1)-positive cells in some tissues. As with previously cloned Siglec-3-related mSiglecs, the lack of strong sequence similarity to a singular hSiglec made identification of the human ortholog difficult. We therefore conducted a comprehensive comparison of Siglecs between the human and mouse genomes. The mouse genome contains eight Siglec genes, whereas the human genome contains 11 Siglec genes and a Siglec-like gene. Although a one-to-one orthologous correspondence between human and mouse Siglecs 1, 2, and 4 is confirmed, the Siglec-3-related Siglecs showed marked differences between human and mouse. We found only four Siglec genes and two pseudogenes in the mouse chromosome 7 region syntenic to the Siglec-3-related gene cluster on human chromosome 19, which, in contrast, contains seven Siglec genes, a Siglec-like gene, and thirteen pseudogenes. Although analysis of gene maps and exon structures allows tentative assignments of mouse-human Siglec ortholog pairs, the possibility of unequal genetic recombination makes the assignments inconclusive. We therefore support a temporary lettered nomenclature for additional mouse Siglecs. Current information suggests that mSiglec-F is likely a hSiglec-5 ortholog. The previously reported mSiglec-3/CD33 and mSiglec-E/MIS are likely orthologs of hSiglec-3 and hSiglec-9, respectively. The other Siglec-3-like gene in the cluster (mSiglec-G) is probably a hSiglec-10 ortholog. Another mouse gene (mSiglec-H), without an apparent human ortholog, lies outside of the cluster. Thus, although some duplications of Siglec-3-related genes predated separation of the primate and rodent lineages (about 80 -100 million years ago), this gene cluster underwent extensive duplications in the primate lineage thereafter.Siglecs 1 (sialic acid-binding immunoglobulin superfamily lectins) are a family of cell surface proteins defined by certain shared structural motifs in the first two Ig-like domains and by their ability to recognize sialic acids via the first Ig V-set domain (1-4). Each Siglec has a distinct expression pattern (3, 4), suggesting that these molecules play unique roles in the cells expressing them. In humans, ten canonical Siglecs (3-5) and one Siglec-like molecule (6, 7) have been reported so far, and our analysis of human genome sequences suggests that there is only one additional Siglec.

Large-scale sequencing of the CD33-related Siglec gene cluster in five mammalian species reveals rapid evolution by multiple mechanisms

“…Siglec molecules have multiple extracellular Ig-like domains (ranging from 2 to 17, each encoded by a single exon), followed by a single-pass transmembrane domain and a cytoplasmic tail. Although genes for 11 functional Siglecs and 1 Siglec-like protein are present in the human genome, only 8 are known in the mouse genome (5). This species difference largely reflects the CD33-related Siglecs (CD33rSiglecs), a subgroup defined by their mutual sequence similarity and clustered gene localization.…”

“…CD33 (also known as Siglec-3) was the first to be discovered among this subgroup of Siglecs (originally as a cell-surface marker of human myeloid cells), hence the group was named after it. Seven functional Siglec genes (CD33͞Siglec-3 and Siglec-5-10) and a Siglec-like gene (Siglec-L1, here renamed Siglec-XII) reside within an Ϸ0.5-Mb region of human chromosome 19q13.3-q13.4, whereas only four Siglec genes occur in the syntenic region of mouse chromosome 7B2 (5).…”

High Resolution Crystal Structures of Siglec-7

“…However, Siglec-9 cannot bind ␣(2,8)-linked disialic acids and prefers ␣(2,3)-and ␣(2,6)-linked terminal sialic acids (2,15,16). Using protein chimeras, this difference in sialic acid linkage preference was recently shown to reside in a 6-amino acid stretch within the C-CЈ loop of * This work was funded by Biotechnology and Biological Sciences Research Council Grant 94/B14010.…”

Cloning and Characterization of Human Siglec-11

“…8 of Ref. 44), it is likely that Siglec-10/Siglec-11 clade (including Siglec-P16) diverged earlier from the rest of CD33/Siglec-3-related group of Siglecs. In other words, it is likely that a Siglec-10/Siglec-11-like gene was ancestral to all other CD33/ Siglec-3-related Siglecs.…”

“…This bacterial artificial chromosome clone was localized on cytological band 19q13.3-13.4 (45), but it does not fall within the CD33/Siglec-3-related gene cluster on the cytological band 19q13.4 (44). Rather, it is located about 1 Mb upstream of the cluster (according to the bacterial artificial chromosome tile mapping by the Lawrence Livermore National Laboratory; greengenes.llnl.gov/genome-bin/ loadmap?regionϭmq).…”