Radical S -adenosyl methionine domain containing-1 (rsad1): A novel gene essential for cell survival during vertebrate development

Raegan D Hunt, The University of Texas Graduate School of Biomedical Sciences at Houston


Vertebrate embryonic development is an intricate process directed by complex molecular instructions. Knowledge about the genes and pathways required for fetal development can be applied to understanding human congenital malformations. Congenital heart disease occurs in 1:100 live births and is the most common birth defect. Deletions involving human chromosome 17q21.3-q24 result in congenital heart defects. The causative gene(s) have not been identified. Syntenic deletions on mouse chromosome 11 have narrowed this critical region for cardiovascular development to an interval containing approximately fifty known and predicted genes. We characterized a novel gene, previously a predicted open reading frame for hypothetical protein FJ1 1164, which falls within this chromosomal interval. The gene for FLJ1164 is highly conserved in vertebrates and encodes a protein with iron-sulfur cluster and S-adenosyl methionine (SAM) binding motifs. Homology searches reveal that the protein product is a member of the emerging radical SAM enzyme superfamily; therefore, we designated the hypothetical gene radical SAM domain containing-1 (rsad1). Although RSAD1 shares sequence identity with a bacterial heme biosynthetic pathway enzyme, biochemical and genetic experiments reveal that it does not retain oxygen-independent coproporphyrinogen oxidase activity. Inconsistent with a role in heme biosynthesis, rsad1 is highly expressed in adult heart and ubiquitously expressed in human fetal organs. Targeted depletion of rsad1 in zebrafish results in embryonic lethality. rsad1 deficient zebrafish embryos exhibit dysmorphic hearts and massive pericardial edema. In addition, phenotypic abnormalities are found in tissues derived from all three germ layers. Affected embryos demonstrate significantly increased apoptotic cell death in tissues characterized by high rsad1 expression. Treatment with caspase inhibitor Z-VAD-FMK or overexpression of the anti-apoptotic protein BCL-2 rescues the rsad1 depletion phenotype. As RSAD1 localizes to the mitochondria, RSAD1 may function as an anti-apoptotic regulator of the programmed cell death pathway. Alternatively, RSAD1 functions in a manner essential for cell survival, and apoptosis is triggered in its absence. This work establishes rsad1 as a novel vertebrate gene required for embryonic development and as a candidate gene for human congenital heart disease. Phenotypic rescue of rsad1 depleted embryos by Z-VAD-FMK provides a potential therapeutic strategy for the treatment of rsad1 deficiency.

Subject Area

Molecular biology|Biochemistry

Recommended Citation

Hunt, Raegan D, "Radical S -adenosyl methionine domain containing-1 (rsad1): A novel gene essential for cell survival during vertebrate development" (2006). Texas Medical Center Dissertations (via ProQuest). AAI3328246.