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 of modifications, including sulfation, 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 the patterning of the nervous system. However, the role of HS 3-O sulfation, the most rare HS modification has not been established. Vertebrate genomes code for at least seven members of the HS 3O-sulfotranferase gene family and are grouped into two distinct classes. We have identified one gene coding for a predicted HS 3O-sulfotranferase of each class in the C. elegans genome which we have named
hst-3.1 and
hst-3.2, respectively. Reporter analyses of
hst-3.1 and
hst-3.2 reveal discrete, largely complementary expression patterns. The
hst-3.2 reporter is primarily expressed in ectodermal tissues (hypodermis and neurons) whereas the
hst-3.1 reporter shows expression in body wall muscle and a few select neurons. Defects in synaptic branch formation and axon termination in select neurons are observed in
hst-3.2 mutants; indicating that
hst-3.2 is required for the proper development of subset of neurons. In addition, perturbations in behaviors regulated by the affected neurons are observed in the
hst-3.2 mutants. Some of the phenotypes identified in the
hst-3.2 mutants are shared by mutations in
rpm-1, a conserved regulator of pre-synaptic maturation (Schaefer et al., 2000; Zhen et al., 2000). Double and triple mutant analyses indicate that
rpm-1 and
hst-3.2 act in parallel genetic pathways. Our data suggests that HS 3-O sulfation, introduced by
hst-3.2, may be a crucial determinant of and/or be part of a novel pathway in the establishment of neuronal connectivity.