CNS glycosylphosphatidylinositol deficiency results in delayed white matter development, ataxia and premature death in a novel mouse model

Abstract

The glycosylphosphatidylinositol (GPI) anchor is a post-translational modification added to approximately 150 different proteins to facilitate proper membrane anchoring and trafficking to lipid rafts. Biosynthesis and remodeling of the GPI anchor requires the activity of over 20 distinct genes. Defects in the biosynthesis of GPI anchors in humans lead to inherited glycosylphosphatidylinositol deficiency (IGD). IGD patients display a wide range of phenotypes though the central nervous system (CNS) appears to be the most commonly affected tissue. A full understanding of the etiology of these phenotypes has been hampered by the lack of animal models due to embryonic lethality of GPI biosynthesis gene null mutants. Here we model IGD by genetically ablating GPI production in the CNS with a conditional mouse allele of phosphatidylinositol glycan anchor biosynthesis, class A (Piga) and Nestin-Cre. We find that the mutants do not have structural brain defects but do not survive past weaning. The mutants show progressive decline with severe ataxia consistent with defects in cerebellar development. We show that the mutants have reduced myelination and defective Purkinje cell development. Surprisingly, we found that Piga was expressed in a fairly restricted pattern in the early postnatal brain consistent with the defects we observed in our model. Thus, we have generated a novel mouse model of the neurological defects of IGD which demonstrates a critical role for GPI biosynthesis in cerebellar and white matter development.

Limb-clasping, cognitive deficit and increased vulnerability to kainic acid-induced seizures in neuronal glycosylphosphatidylinositol deficiency mouse models

“…None of the mutants survived past weaning, with 50% hemizygous cko not surviving 2 days after birth and 50% of mosaic cko not surviving 19 days after birth. The brain size of mutants was smaller than that of WT ( 18 ). In the current study, we used Emx1-Cre , Vgat-Cre and Pkcd-Cre mouse lines to target ablation to telencephalon excitatory neurons, inhibitory neurons and thalamic neurons, respectively.…”

“…All of the mosaic mutants and thalamus-specific hemizygous mutants (Th-H-cko) could survive as long as control mice, at least for 1 year. These data suggested that the short life span in Nestin-Cre -induced Piga mosaic mutants (Nestin-M-cko) ( 18 ) was more likely due to the deficits of GPI anchors in non-neuronal cells including astrocytes and oligodendrocytes.…”

“…These mutated mice showed deficits in cerebellar and white matter development, ataxia and tremor and did not survive past weaning. The early lethality of these mice excludes the possibility to examine their cognitive and epileptic phenotype thoroughly ( 18 ). In addition, Nestin is also expressed in a variety of tissues and progenitor cells, including pancreatic islets, skeletal muscle satellite cells, developing myotomes, testis, hair follicle, heart and the non-hematopoietic fraction of the bone marrow ( 19 ), further adding to the complexity of explaining the mutants’ phenotype.…”

Limb-clasping, cognitive deficit and increased vulnerability to kainic acid - induced seizures in neuronal GPI anchor deficiency mouse models

“…In the Piga flox mouse line, three loxP sites with identical orientation were inserted within the Piga gene on X chromosome, with one loxP localized in intron 5 and the other two loxP sites flanking a Neo gene localized downstream of exon 6 (Fig1.A). Previous work using this mouse line proved that deletion of exon 6 upon Cre recombination resulted in an efficient ablation of Piga and disrupted the cell surface expression of GPI-APs (16)(17)(18)20). Our In situ hybridization on adult mouse brain showed that Piga is widely expressed in almost all the neurons, and has a very strong expression in CA1 pyramidal cells and dentate gyrus (DG) granule cells of the hippocampus, and piriform cortex (Fig1.B).…”

“…These mutated mice showed deficits in cerebellar and white matter development, ataxia and tremor, and did not survive past weaning. The early lethality of these mice exclude the possibility to examine their cognitive and epileptic phenotype thoroughly (18). In addition, Nestin is also expressed in a variety of tissues and progenitor cells, including pancreatic islets , skeletal muscle satellite cells, developing myotomes, testis, hair follicle, heart, and the non-hematopoietic fraction of the bone marrow (19), further adding to the complexity of explaining the mutants' phenotype.…”