Glycosylphosphatidylinositol biosynthesis and remodeling are required for neural tube closure, heart development, and cranial neural crest cell survival.

Marshall Lukacs,Praneet Chatuverdi,Tia Roberts,Rolf W Stottmann

doi:10.7554/elife.45248

Abstract

Glycosylphosphatidylinositol (GPI) anchors attach nearly 150 proteins to the cell membrane. Patients with pathogenic variants in GPI biosynthesis genes develop diverse phenotypes including seizures, dysmorphic facial features and cleft palate through an unknown mechanism. We identified a novel mouse mutant (cleft lip/palate, edema and exencephaly; Clpex) with a hypo-morphic mutation in Post-Glycophosphatidylinositol Attachment to Proteins-2 (Pgap2), a component of the GPI biosynthesis pathway. The Clpex mutation decreases surface GPI expression. Surprisingly, Pgap2 showed tissue-specific expression with enrichment in the brain and face. We found the Clpex phenotype is due to apoptosis of neural crest cells (NCCs) and the cranial neuroepithelium. We showed folinic acid supplementation in utero can partially rescue the cleft lip phenotype. Finally, we generated a novel mouse model of NCC-specific total GPI deficiency. These mutants developed median cleft lip and palate demonstrating a previously undocumented cell autonomous role for GPI biosynthesis in NCC development.

Highlights

Inherited glycophosphatidylinositol deficiency (IGD) disorders are a class of congenital disorders of glycosylation that affect the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor
We found by mapping and whole exome sequencing the Clpex mutation is a homozygous missense allele in the initiating methionine of Post-Glycophosphatidylinositol Attachment to Proteins-2 (Pgap2), the final enzyme in the GPI biosynthesis pathway
The Clpex allele failed to complement a null allele of Pgap2, confirming the Clpex mutant is caused by a hypomorphic mutation in Pgap2

Summary

Introduction

Inherited glycophosphatidylinositol deficiency (IGD) disorders are a class of congenital disorders of glycosylation that affect the biosynthesis of the glycosylphosphatidylinositol (GPI) anchor. Autosomal recessive mutations in PGAP2 cause Hyperphosphatasia with Mental Retardation 3 (HPMRS3 OMIM # 614207), an IGD that presents with variably penetrant hyperphosphatasia, developmental delay, seizures, microcephaly, heart defects, and a variety of neurocristopathies including Hirschsprung’s disease, cleft lip, cleft palate, and facial dysmorphia [5,6,7,8]. As we observed tissue specific defects in NCCs in the Clpex germline mutant, we sought to determine the cell autonomous requirement for GPI biosynthesis pathway generally in NCC development. The Clpex mutant and our NCC conditional mutant serve as models for studying the effect of GPI biosynthesis defects in development of the craniofacial complex and testing potential therapeutics in utero for patients

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