An exon 10 deletion in the mouse ferrochelatase gene has a dominant-negative effect and causes mild protoporphyria.
Protoporphyria is generally inherited as an autosomal dominant disorder. The enzymatic defect of protoporphyria is a deficiency in ferrochelatase, which chelates iron and protoporphyrin IX to form heme. Patients with protoporphyria have decreased ferrochelatase activities that range from 5% to 30% of normal caused by heterogeneous mutations in the ferrochelatase gene. The molecular mechanism by which the ferrochelatase activity is decreased to less than an expected 50% is unresolved. In this study, we assessed the effect of a ferrochelatase exon 10 deletion, a common mutation in human protoporphyria, introduced into the mouse by gene targeting. F1 crosses produced (+/+), (+/-), and (-/-) mice at a ratio of 1:2:0; (-/-) embryos were detected at 3.5 days postcoitus, consistent with embryonic lethality for the homozygous mutant genotype. Heterozygotes demonstrated equivalent levels of wild-type and mutant ferrochelatase messenger RNAs and 2 immunoreactive proteins that corresponded to the full-length and an exon 10-deleted ferrochelatase protein. Ferrochelatase activities in the heterozygotes were an average of 37% of normal, and protoporphyrin levels were elevated in erythrocytes and bile. Heterozygous mice exhibited skin photosensitivity but no liver disease. These results lend support for a dominant-negative effect of a mutant allele on ferrochelatase activity in patients with protoporphyria.
Magness
Scott T
ST
Department of Medicine, University of North Carolina at Chapel Hill 27599, USA.
Maeda
Nobuyo
N
Brenner
David A
DA
D000483:Alleles; D000818:Animals; D001646:Bile / Q000737:chemistry; D003433:Crosses, Genetic; D004912:Erythrocytes / Q000737:chemistry; D005091:Exons; D005294:Ferrochelatase / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D018390:Gene Targeting; D006579:Heterozygote; D015151:Immunoblotting; D051379:Mice; D018345:Mice, Knockout; D010787:Photosensitivity Disorders / Q000235:genetics; D017121:Porphyria, Hepatoerythropoietic / Q000201:enzymology / Q000235:genetics*; D011524:Protoporphyrins / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis
D011524:Protoporphyrins; D012333:RNA, Messenger; D005294:Ferrochelatase