Genomic and biochemical characterization of sialic acid acetylesterase (siae) in zebrafish.

Sialic acid acetylesterase (SIAE) removes acetyl moieties from the carbon 9 and 4 hydroxyl groups of sialic acid and recently a debate has been opened on its association to autoimmunity. Trying to get new insights on this intriguing enzyme we have studied siae in zebrafish (Danio rerio). In this teleost siae encodes for a polypeptide with a high degree of sequence identity to human and mouse counterparts. Zebrafish Siae behavior upon transient expression in COS7 cells is comparable to human enzyme concerning pH optimum of enzyme activity, subcellular localization and glycosylation. In addition, and as already observed in case of human SIAE, the glycosylated form of the enzyme from zebrafish is released into the culture media. During embryogenesis, in situ hybridization experiments demonstrate that siae transcript is always detectable during development, with a more specific expression in the central nervous system, in pronephric ducts and liver in the more advanced stages of the embryo development. In adult fish an increasing amount of siae mRNA is detectable in heart, eye, muscle, liver, brain, kidney and ovary. These results provide novel information about Siae and point out zebrafish as animal model to better understand the biological role(s) of this rather puzzling enzyme in vertebrates, regarding immune system function and the development of central nervous system.