A GPI processing phospholipase A2, PGAP6, modulates Nodal signaling in embryos by shedding CRIPTO

Area of Science:

• Cell Biology
• Biochemistry
• Developmental Biology

Background:

• Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are released from cell membranes via GPI cleavage.
• The precise mechanisms and enzymes involved in shedding specific GPI-APs, like CRIPTO, remain incompletely understood.

Purpose of the Study:

• To identify and characterize novel enzymes involved in GPI-AP shedding.
• To investigate the role of a newly discovered enzyme, PGAP6, in the processing and shedding of CRIPTO.
• To elucidate the functional consequences of PGAP6-mediated CRIPTO shedding on Nodal signaling and embryonic development.

Main Methods:

• Biochemical assays to characterize enzyme activity.
• Cell surface protein analysis using PGAP6 expression.
• CRISPR-Cas9 gene editing to create Pgap6 knockout mice.
• Analysis of embryonic development in Pgap6 knockout mice.

Main Results:

• A novel cell surface enzyme, post-glycosylphosphatidylinositol attachment to proteins 6 (PGAP6), was identified as a GPI-specific phospholipase A2.
• PGAP6 efficiently cleaves and sheds CRIPTO, a critical GPI-anchored coreceptor for Nodal signaling in early embryonic development.
• Shed CRIPTO retains activity as a Nodal coreceptor, while PGAP6 expression reduces cell-associated CRIPTO activity.
• Pgap6 knockout mice exhibit severe defects in early embryonic development, including anterior-posterior axis formation, mirroring Cripto knockout phenotypes.

Conclusions:

• PGAP6 is a key enzyme responsible for shedding CRIPTO, modulating its availability and activity.
• PGAP6-mediated CRIPTO shedding plays a critical role in regulating Nodal signaling pathways essential for embryonic development.
• The findings highlight PGAP6 as a significant factor in controlling developmental processes through the regulation of GPI-anchored proteins.