Uncovering the heparan sulfate domain topography of C. elegans using a novel heparan sulfate domain visualization system

Abstract

Heparan sulfate (HS) is a long, linear glycosaminoglycan (GAG) attached to core proteins forming extracellular HS proteoglycans. HS domains are stretches of modification patterns encoded onto HS GAGs by HS modifying enzymes and are interspersed by areas lacking modifications. These domains provide the binding sites for various extracellular proteins. It is this function that makes them necessary in the development of animal life. The utility of HS domains in development suggests they would be produced in a cell- or tissue-specific fashion, forming a topographic map of differently modified HS domains so as to encourage specific protein interactions and direct development in a spatially and temporally controlled manner. An approach to study this HS domain topography in living animals does not exist. Here I describe a novel method for the visualization of HS domains in vivo. This method uses single chain variable fragment (scFv) antibodies previously identified as binding HS domains. Engineered around these scFv antibodies is a modular system composed of a Caenorhabditis elegans promoter sequence to drive expression of the transgene, a signal sequence for secretion into the body cavity, and a fluorescent tag for visualization. Using this method, HS domains can be visualized throughout development from the embryo to the adult. HS domains can now easily be targeted for genetic analysis to determine the composition of the recognized HS domain and the genes directing its formation. This method reveals a HS domain topography that includes common and more widespread HS domains and HS domains that label discrete regions of the nervous system, alimentary system, and muscles. The HS domain topography of the nervous system has surprising cell- and subcellular-specificity. In general, in the nervous system the HS domains are associated with neurites rather than the soma. Cell-specific HS domains in the nervous system are associated with two pairs of neurons in the nerve ring and are found where these neurons form synapses. This anatomical association is partially conserved through evolution. The HS topology of C. elegans suggests HS domain may play a role in forming specific connections in the nervous system.