Syndecan 4 interacts genetically with Vangl2 to regulate neural tube closure and planar cell polarity

Area of Science:

• Developmental Biology
• Cell Signaling
• Genetics

Background:

• Syndecan 4 (Sdc4), a cell-surface heparan sulfate proteoglycan (HSPG), is crucial for embryonic development, including gastrulation and neural tube closure.
• The Wnt/Planar Cell Polarity (PCP) pathway is essential for coordinating cell behaviors during development.
• Vangl2 is a key component of the Wnt/PCP pathway, and mutations can lead to developmental defects.

Purpose of the Study:

• To investigate the potential role of Syndecan 4 (Sdc4) in Wnt/PCP signaling during mammalian development.
• To determine if Sdc4 genetically interacts with Vangl2 in mouse development.
• To elucidate the molecular mechanisms underlying the interaction between Sdc4 and Vangl2.

Main Methods:

• Generation and analysis of compound mutant mice lacking Sdc4 and carrying the Vangl2 loop-tail (Lp) allele.
• Assessment of neural tube closure, cochlear stereocilia bundle orientation, and wound healing in mutant mice.
• Experimental manipulation of Sdc4 and Vangl2 expression in HEK293 cells and Xenopus embryos.
• In vivo studies using sulfation inhibitors (chlorate) to assess the role of heparan sulfate residues.

Main Results:

• Compound Sdc4;Vangl2(Lp) mutant mice exhibit severe defects in spinal neural tube closure, stereocilia orientation, and wound healing, indicating a strong genetic interaction.
• Co-injection of suboptimal Sdc4 and Vangl2 morpholinos in Xenopus embryos resulted in significantly increased neural tube closure defects compared to individual morpholinos.
• Sdc4 and Vangl2 proteins colocalize in cells; Vangl2 (especially the Lp mutant) reduces Sdc4 levels, while Vangl2 knockdown increases Sdc4 levels, suggesting Vangl2 regulates Sdc4 protein stability.
• Vangl2 influences overall HSPG levels, and Vangl2(Lp/+) embryos treated with chlorate show impaired neural tube closure, suggesting a role for heparan sulfate modification.

Conclusions:

• Syndecan 4 (Sdc4) actively participates in the Wnt/PCP pathway.
• Sdc4 plays a critical role in mammalian neural tube closure, interacting genetically with Vangl2.
• The findings highlight a novel mechanism involving Sdc4 and Vangl2 in regulating developmental processes through HSPG modification.