Syndecan defines precise spindle orientation by modulating Wnt signaling in C. elegans

Abstract

Wnt signals orient mitotic spindles in development, but it remains unclear how Wnt signaling is spatially controlled to achieve precise spindle orientation. Here, we show that C. elegans syndecan (SDN-1) is required for precise orientation of a mitotic spindle in response to a Wnt cue. We find that SDN-1 is the predominant heparan sulfate (HS) proteoglycan in the early C. elegans embryo, and that loss of HS biosynthesis or of the SDN-1 core protein results in misorientation of the spindle of the ABar blastomere. The ABar and EMS spindles both reorient in response to Wnt signals, but only ABar spindle reorientation is dependent on a new cell contact and on HS and SDN-1. SDN-1 transiently accumulates on the ABar surface as it contacts C, and is required for local concentration of Dishevelled (MIG-5) in the ABar cortex adjacent to C. These findings establish a new role for syndecan in Wnt-dependent spindle orientation.

Gradient-independent Wnt signaling instructs asymmetric neurite pruning in C. elegans

“…Alternatively, it is also possible that the gradient-independent or contact-dependent processes require transmembrane co-factors that mediate contact-dependent Wnt signaling. sdn-1/syndecan was one such candidate as it has been shown that sdn-1 is required for the Wnt-dependent spindle orientation in early embryonic development (Dejima et al, 2014), and sdn-1 mutants exhibit PDB structure defects similar to lin-44/wnt (Saied-Santiago et al, 2017). However, we did not observe significant pruning defects in PDB of sdn-1 mutants (data not shown).…”