Disruption of <i>Iqsec1</i> in mice leads to embryonic lethality with reduced large apical vacuoles in the visceral endoderm

Iqsec1 (IQ motif and Sec7 domain-containing protein 1), also known as BRAG2 (Brefeldin A-resistant Arf-GEF 2), is a guanine nucleotide exchange factor that regulates membrane trafficking, cytoskeletal organization, and signal transduction by activating class II and III ADP-ribosylation factors. To investigate the physiological role of Iqsec1 at the whole animal level, we generated Iqsec1-deficient mice using CRISPR/Cas9-mediated gene editing. Nearly all Iqsec1^-/- mice (99%) exhibited embryonic lethality with severe growth retardation. Electron microscopy revealed that Iqsec1^-/- embryos at embryonic day 8.5 lacked large apical vacuoles in visceral endoderm cells of the yolk sac, compared with controls. These findings suggest that Iqsec1 plays a critical role in embryogenesis, likely through regulation of membrane trafficking in visceral endoderm cells.