Disease relevance of Piga

• GATA1-Cre mediates Piga gene inactivation in the erythroid/megakaryocytic lineage and leads to circulating red cells with a partial deficiency in glycosyl phosphatidylinositol-linked proteins (paroxysmal nocturnal hemoglobinuria type II cells) [1].
• Finally, since the dual abnormalities in the lamellar body secretory system and filaggrin processing resemble two key features of human Harlequin ichthyosis, Pig-a null mice could provide an appropriate analog for further studies of this disease [2].
• Female embryos in which one Pig-a allele was disrupted by Cre such that only half of the cells in the embryo proper did not express GPI-anchored proteins due to random X inactivation developed until 19 days post coitum (dpc), but showed abnormal phenotypes such as insufficient closure of neural tube and cleft palate [3].
• Currently there is no experimental animal model for studying paroxysmal nocturnal hemoglobinuria (PNH), an acquired hemolytic anemia linked to mutations of the PIG-A gene [4].
• Direct evidence for the involvement of GPI or GPI-anchored proteins in the HgCl2-mediated signaling is provided by the loss of signaling in a mutant thymoma cell line defective in the phosphatidylinositol glycan-class A gene (PIG-A), and its restoration in a transfectant with PIG-A [5].

High impact information on Piga

• Deficiency of the GPI anchor caused by a somatic mutation of the PIG-A gene in paroxysmal nocturnal hemoglobinuria [6].
• To inactivate the murine Piga gene in early hematopoiesis we therefore chose conditional gene inactivation using the Cre/loxP system [7].
• Using bone marrow reconstitution experiments with purified PIGA(-) cells we demonstrate that LF mice have long-term bone marrow repopulating cells that lack GPI-linked proteins, indicating that recombination of the floxed Piga allele occurs in the hematopoietic stem cell [7].
• In transgenic mice, germline transmission of an inactive Piga gene is embryonic lethal [7].
• Although the PIG-A mutation explains the phenotype of PNH cells, the mechanism enabling the PNH stem cell to expand is not clear [8].

Biological context of Piga

• Mapping of Piga to the X chromosome suggests that a single acquired mutation within Piga could alter GPI-anchor synthesis and result in PNH [9].
• X inactivation and somatic cell selection rescue female mice carrying a Piga-null mutation [10].
• The effect of GPI-anchor deficiency on apoptosis in mice carrying a Piga gene mutation in hematopoietic cells [11].
• High-dose cyclophosphamide does not eradicate paroxysmal nocturnal haemoglobinuria haematopoiesis in mice carrying a Piga gene mutation [12].
• We disrupted the Pig-a gene, an X-linked gene essential for GPI-anchor biosynthesis, in skin [13].

Anatomical context of Piga

• A human cDNA, Piga, that repairs cell lines with the class A GPI-anchor biosynthetic defect has been recently cloned [9].
• Mice that are mosaics for the recombined Piga gene are viable and lack GPI-linked proteins on a proportion of circulating blood cells [14].
• Increased sensitivity to complement and a decreased red blood cell life span in mice mosaic for a nonfunctional Piga gene [14].
• We transplanted lethally irradiated mice with female fetal liver cells bearing one allele of the Piga gene disrupted by conditional gene targeting [15].
• Recombination of the floxed Piga allele was also detected in cultured megakaryocytes, mast cells, and eosinophils, but not in neutrophils, lymphocytes, or nonhematopoietic tissues [1].

Associations of Piga with chemical compounds

• Mice with targeted Piga gene inactivation genetically mimic the human disease and have phosphatidylinositol glycan class A-negative (PIGA-) RBCs with a reduced half-life in circulation [16].
• All patients with PNH studied so far have a somatic mutation of phosphatidyl inositol glycan complementation group A (PIG-A), an X-linked gene involved initially in the biosynthesis of the glycosyl phosphatidylinositol (GPI) molecule, which serves as an anchor for many cell surface proteins [17].

Other interactions of Piga

• In contrast to Piga, both human and mouse Pigf and Pigh genes map to autosomes [9].
• In summary, GATA1-Cre causes high-efficiency Piga gene inactivation in a GATA-1-specific pattern [1].
• Here we analyzed keratinocytes of the female K5-Cre: Pig-a flox/+ mice with heterozygous knockout of Pig-a. These cells exhibited the mosaic pattern of GPI-anchor positive and negative expression typical of random inactivation of the X chromosome [18].

Analytical, diagnostic and therapeutic context of Piga

• We therefore treated mice that have a proportion of blood cells deficient in GPI-anchor molecules (PIGA-) with HD CY, and monitored their peripheral blood counts during and after treatment [12].
• We therefore used site-directed mutagenesis to create conservative mutations in the Pig-a protein, then performed structural and functional analysis [19].
• DNA chip analysis of multiple paired normal and PIG-A mutant cell lines and lymphoblastoid cells do not show any consistent differences in levels of gene expression [20].

References