Our lab is interested in how Heparan Sulfate (HS) modifications regulate neuronal connectivity and patterning in C. elegans. HS is a highly modified un-branched glycosaminoglycan exhibiting substantial molecular diversity due to multiple modifications such as sulfations, epimerization and acetylation. HS modifications have been documented to have specific and instructive roles (Bulow and Hobert, 2004; Bulow et al., 2008) in neuronal development leading to the hypothesis of a HS code that regulates nervous system patterning. However, the role of the 3-O sulfation modification of HS, introduced by heparan sulfotransferase 3 enzymes (HST-3s), has not been established. Vertebrate genomes code for at least seven members of the HST-3 gene family that are grouped into two distinct classes. A subset of the vertebrate HST-3s display temporarily and spatially restricted expression patterns in the developing and post-natal brain, however, very little is known about the in vivo function of these enzymes in neuronal development due to functional redundancy. We have identified one gene coding for a predicted HST-3 of each class in the C. elegans genome:
hst-3.1 and
hst-3.2. Analysis of neuronal patterning in null mutants of
hst-3.1 and
hst-3.2 indicates that both genes are required for synaptic branch formation in a subset of C. elegans neurons. In addition,
hst-3.2 may play a role in axon termination. These phenotypes are reminiscent of mutations in genes regulating synaptic maturation and/or function. Therefore, on going experiments are focused on determining if loss of
hst-3.2 and/or
hst-3.1 results in synaptic disorganization and if either gene acts in known synaptic pathways. We have recently elucidated that several other null mutants of HS modification enzymes and HS core proteins share the phenotypes that we identified in null mutants of
hst-3.1 and
hst-3.2. We are investigating the interaction of HS modifications and core proteins, via double and triple mutant analysis, in various cellular contexts. Furthermore, we are determining the cellular focus of action of the HS 3O-sulfotransferases. This analysis will provide invaluable insight into possible mechanisms by which the HS code regulates neuronal development and patterning.