The microcephaly-associated protein YIPF5 differentially regulates ER export.

YIPF5 is an ER-membrane protein implicated in ER-Golgi transport. Mutations in YIPF5 cause MEDS2 (microcephaly, epilepsy, and neonatal diabetes syndrome), a fatal disorder manifesting in early childhood. We demonstrate that YIPF5 is involved in ER export of a subset of proteins, including cargoes of the ER export receptor SURF4, with which it directly interacts. YIPF5 knockout cells display altered cell surface and secretome profiles, with reduced neuronal adhesion molecules and increased secretion of ER chaperones affecting migration. YIPF5 depletion enhances cell migration in a wound-healing assay and alters SURF4 localization, causing elongated ERGIC53- and Rab1-positive tubules from ER exit sites. Kinetic analysis suggests that YIPF5 negatively regulates SURF4-mediated ER export. In utero knockdown of Yipf5 in embryonic mouse brains induces premature neuronal migration and abnormal neuronal morphology. Our findings suggest that YIPF5 and SURF4 coordinate ER export of key proteins and disruption may underlie cortical development defects leading to microcephaly.