Identification of a novel nonlysosomal sulphatase expressed in the floor plate, choroid plexus and cartilage

Background: Sulphated glycosaminoglycans (GAGs) attached to proteoglycan core proteins are implicated in cell adhesion, motility and morphogenesis. Variable sulphation patterns, which are thought to be important for regulating proteoglycan function, are generated by sequential reactions during GAG biosynthesis. However, the mechanism by which such diversity is generated remains unclear. Results: A novel sulphatase, designated RsulfFP1, was isolated from rat embryos by screening for floor plate specific genes. RsulfFP1 and its orthologues show homology with other sulphatases, and have a distinctive hydrophilic insertion. In situ hybridization showed that RsulfFP1 mRNA is strongly expressed in the floor plate, choroid plexus and cartilage in rat embryos. lit vitro transfection experiments revealed that the RsulfFP1 protein is localized to the Golgi apparatus and endoplasmic reticulum, and is not present in the lysosomes. It also appears to be localized on the cell surface. Conclusions: RsulfFP1, a phylogenetically conserved sulphatase, forms a novel subgroup in the sulphatase family. It shows homology with the lysosomal sulphatases involved in GAG degradation. Localization of the RsulfFP1 protein in the Golgi apparatus and on the cell surface, however, suggests that it may play a role in regulating proteoglycan-mediated signalling by the desulphation of GAGs during biosynthesis or after GAGs are presented in the extracellular space.