Distinct 3-O-sulfated heparan sulfate modification patterns are required for kal-1 dependent neurite branching in a context-dependent manner in C. elegans
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Heparan sulfate (HS) is an un-branched glycosaminoglycan exhibiting substantial molecular diversity due to multiple, non-uniformly introduced modifications including sulfations, epimerization and acetylation. HS modifications serve specific and instructive roles in neuronal development leading to the hypothesis of a HS code that regulates nervous system patterning. While the in vivo roles of many of the HS modifications have been investigated, very little is known about the function of HS 3- O-sulfation in vivo. By examining patterning of the C. elegans nervous system in loss of function mutants of the two 3-O-sulfotransferases, hst-3.1 and hst-3.2, HS 3-O-sulfation was found to be largely dispensable for overall neural development. However, generation of stereotypical axonal branches in hermaphroditic specific neurons (HSN) required hst-3.1, hst-3.2 as well as an extracellular cell adhesion molecule encoded by kal-1, the homolog of Kallmann Syndrome associated gene 1/anosmin-1. In contrast, kal-1 dependent neurite branching in AIY neurons required catalytic activity of hst-3.2 but not hst-3.1. The context dependent requirement for hst-3.2 and hst-3.1 indicates that both enzymes generate distinct types of HS modification patterns in different cell types, which regulate kal-1 to promote neurite branching. HS 3-O-sulfation does not play a general role in establishing the HS code in C. elegans, but rather plays a specialized role in a context dependent manner to establish defined aspects of neuronal circuits.