Equine pre-implantation conceptuses express neuraminidase 2 - a potential mechanism for desialylation of the equine capsule

During the second and third week of pregnancy, the equine conceptus is covered by an acellular glycoprotein capsule. This capsule contains glycoproteins resembling those of the mucin family with sialic acid making up a high proportion of the carbohydrate. Coinciding with conceptus fixation, a marked decline in sialic acid content of the capsule occurs, which has been proposed to contribute to cessation of conceptus mobility. Herein, we describe the expression of neuraminidase 2 (NEU2) by pre-implantation stages of equine conceptus development. NEU2 transcript abundance was examined in conceptuses obtained 8, 10, 12, 14 and 16days after ovulation; highest levels were observed 16days after ovulation. Transcript abundance observed in endometrial tissue was on average 474-fold lower than in conceptus tissue. Protein expression was localized to trophoblast cells and capsular material. Functionality of NEU2 was shown using an Amplex Red reagent-based assay. NEU2, formerly known as sialidase 2, belongs to a family of enzymes that cleave sialic acid from polysaccharide chains. The expression of NEU2 described herein provides a mechanism by which the conceptus can regulate the sialic acid content of its own capsule. The timely desialylation coinciding with conceptus fixation has been suggested integral for establishment of normal pregnancy.