Glycosyl Phosphatidylinositol Anchor Biosynthesis Is Essential for Maintaining Epithelial Integrity during Caenorhabditis elegans Embryogenesis

Abstract

Glycosylphosphatidylinositol (GPI) is a post-translational modification resulting in the attachment of modified proteins to the outer leaflet of the plasma membrane. Tissue culture experiments have shown GPI-anchored proteins (GPI-APs) to be targeted to the apical membrane of epithelial cells. However, the in vivo importance of this targeting has not been investigated since null mutations in GPI biosynthesis enzymes in mice result in very early embryonic lethality. Missense mutations in the human GPI biosynthesis enzyme pigv are associated with a multiple congenital malformation syndrome with a high frequency of Hirschsprung disease and renal anomalies. However, it is currently unknown how these phenotypes are linked to PIGV function. Here, we identify a temperature-sensitive hypomorphic allele of PIGV in Caenorhabditis elegans, pigv-1(qm34), enabling us to study the role of GPI-APs in development. At the restrictive temperature we found a 75% reduction in GPI-APs at the surface of embryonic cells. Consequently, ~80% of pigv-1(qm34) embryos arrested development during the elongation phase of morphogenesis, exhibiting internal cysts and/or surface ruptures. Closer examination of the defects revealed them all to be the result of breaches in epithelial tissues: cysts formed in the intestine and excretory canal, and ruptures occurred through epidermal cells, suggesting weakening of the epithelial membrane or membrane-cortex connection. Knockdown of piga-1, another GPI biosynthesis enzymes resulted in similar phenotypes. Importantly, fortifying the link between the apical membrane and actin cortex by overexpression of the ezrin/radixin/moesin ortholog ERM-1, significantly rescued cyst formation and ruptures in the pigv-1(qm34) mutant. In conclusion, we discovered GPI-APs play a critical role in maintaining the integrity of the epithelial tissues, allowing them to withstand the pressure and stresses of morphogenesis. Our findings may help to explain some of the phenotypes observed in human syndromes associated with pigv mutations.

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

“…These data are in contrast to previous reports in which some GPI biosynthesis genes are shown to be ubiquitously and uniformly expressed, including Pign in the mouse and pigu in zebrafish (McKean and Niswander, 2012; Nakano et al, 2010). Our Pgap2 expression is more consistent with the expression of Pigv which is enriched in C. elegans epidermal tissues (Budirahardja et al, 2015).…”

Glycosylphosphatidylinositol Biosynthesis and Remodeling are Required for Neural Crest Cell, Cardiac and Neural Development

“…These data are in contrast to previous reports where some GPI biosynthesis genes are shown to be ubiquitously and uniformly expressed, including Pign in the mouse and pigu in zebrafish [10,14]. Our Pgap2 expression is more consistent with the expression of Pigv which is enriched in C. elegans epidermal tissues [15] Pgap2 is required for the proper anchoring of GPI-APs, including FOLR1.…”

Modifiers of solid RNP granules control normal RNP dynamics and mRNA activity in early development

“…Thus, our C. elegans screen links RNP control functions to unpredicted human mRNA-binding proteins that control protein folding (chaperones) and membrane trafficking ( vha genes). Two additional genes support roles of membrane vesicle dynamics ( alfa-1 and pigv-1 ; Farg et al, 2014 ; Budirahardja et al, 2015 ). Interestingly, alfa-1 is a homologue of human c9orf72, which is the most common target of polyQ expansions in some CNS diseases that are linked to RNP aggregation ( Mizielinska and Isaacs, 2014 ).…”