Zygotic Arrest 1 Pathogenic Variants Disrupt Maternal mRNA Stability and Cause Oocyte Maturation Defects in Humans

Zygotic arrest 1 (ZAR1) is one of the earliest identified maternal-effect genes that function during the maternal-to-zygotic transition (MZT) in mice. However, the role of human ZAR1 was unclear. This study investigated the association of ZAR1 gene variants and infertility in women, focusing on their impact on oocyte and early embryonic development. In five individuals with unexplained female infertility, defects in oocyte maturation and early embryonic arrest were observed during in vitro fertilization treatment. Whole-exon sequencing identified either homozygous or compound heterozygous variants of ZAR1 in the patients. Functional analysis revealed that the V118A mutation disrupted the localization of ZAR1 to the mitochondria-associated ribonucleoprotein domain (MARDO) structure, a key mRNA storage site in oocytes. In contrast, R397Q and S121* mutations impaired ZAR1's RNA-binding capability. These variants disrupt MARDO formation and function, thereby negatively affecting oocyte maturation and early embryonic development. Additionally, transcriptome analysis of oocytes and embryos from ZAR1 variant carriers showed downregulation of maternal mRNAs and altered translation profiles, indicating a disrupted MZT. This study highlights the critical roles of ZAR1 and MARDO in human reproduction and provides insights into the molecular mechanisms underlying some forms of female infertility. Overall design: Expression profiling by high throughput sequencing.RNA sequencing (RNA-seq) was applied to both healthy control and patient-derived oocytes at the germinal vesicle (GV) stage, as well as to embryos at the 1-cell stage.