Alterations in sialic-acid O-acetylation glycoforms during murine erythrocyte development

Vinay S. Mahajan; Faisal Alsufyani; Hamid Mattoo; Ian Rosenberg; Shiv Pillai

Sialic acid, a monosaccharide with a nine-carbon backbone, is widely found in nature as a terminal sugar of animal and microbial glycoproteins and glycolipids. It plays important roles in animal development, cellular recognition processes and host-pathogen interactions (Schauer, 2009) . A common modification of sialic acid is 9-O-acetylation, which has been implicated in sialoglycan recognition and ganglioside biology. The hemagglutinins or hemagglutinin-esterases of type C influenza viruses and certain nidoviruses specifically recognize the 9-O-acetylated form of sialic acid, and this form of sialic acid is required for the entry of these viruses into human cells. Although we had previously inferred a role for sialic acid 9-O-acetylation in regulating Siglec-2 (Cariappa et al., 2009) , we have demonstrated that many of the phenotypes on the basis of which earlier conclusions were made, actually resulted from a mutation that was traceable to a commercially available C57BL/6 strain of mice (Mahajan et al., 2016) . , 2015) . Their studies implicated CASD1 in directly transferring acetyl moieties from acetyl-CoA to CMP-sialic acid. Whether CMP-sialic acid is the preferred substrate for the O-acetylation of sialic acid in vivo however remains to be established. In this report, we describe a mouse strain in which Casd1 has been deleted in the germline. Analysis of these mice demonstrated the loss of 9-O-acetylation of sialic acid on the surface of all hematopoietic cells examined. Based on the differential specificity of hemagglutinin O-acetylated sialic acid found on the surface of murine myeloid cells may decorate this glycoprotein. Indeed, mucin-like glycoproteins such as CD43 and CD45RB have been shown to bear 9-O-acetylated sialic acids on mononuclear cells in the spleen (Krishna and Varki, 1997) . No detectable 9-O-acetyl sialic acid was found on the CD11b + CD43 + population in the bone marrows of Casd1-deficient mice (Fig 1C) . A large proportion of CD43 + CD11bnon-myeloid cells, largely hematopoietic progenitors in the bone marrow, also express surface 9-O-acetyl sialic acid in wild type mice but this was completely lost in Casd1-deficient mice (Fig 1C) .