Chimaeric mice with disruption of the gene coding for phosphatidylinositolglycan class A (Pig-a) were defective in embryogenesis and spermatogenesis

Mutations in the gene encoding PIG-A (phosphatidylinositol glycan class A) are found in patients with paroxysmal nocturnal haemoglobinuria (PNH), an a cquired haematopoietic stem cell disorder. Individuals with hereditary PIG- A mutations have never been identified, which is also manifested by the dif ficulties in generating Pig-a knockout (KO) mice. This study investigated t he effect of Pig-a mutations on the development of visceral and genital org ans in addition to the haematopoietic system by the generation of Pig-a KO chimaeric mice. Of a total of 54 live births out of 1684 blastocysts inject ed, chimaerism for rig-a knockout was detected in 29 mice, suggesting the i mportance of Pig-a in embryogenesis and in live birth. Quantification of th e degree of chimaerism in different organs of the surviving chimaeric mice revealed extremely low levels of Pig-a KO cells in the liver and spleen. In contrast, high levels of KO signals were usually detected in the brain, he art, lung and kidney. Haematopoiesis proceeded normally in these chimaeric mice (as measured by 'complete blood cell counting') and the Pig-a KO cells were present at low levels in red blood cells and B lymphocytes but at hig h levels in T lymphocytes, although these KO cells did not gain any growth advantage. The effect of Pig-a knockout was also prominent in the reproduct ive system, another organ with high mitotic activity. Breeding the male chi maeras revealed a high rate of infertility and abnormality in the male geni tal organs, including abnormally shaped testes, epididymis and seminal vesi cles. Even in the absence of gross abnormalities of the genital organs, low counts of motile sperm were also discernible. Pig-a KO sperm was detected in these organs; however, no transmission of the KO allele was observed. Th e results suggest a possible mechanism underlying the non-transmission of t he Pig-a KO gene in germlines.