Paternal knockout of /SNAT4 causes placental hypoplasia associated with intrauterine growth restriction in mice.

The placenta is critical in mammalian embryonic development because the embryo's supply of nutrients, including amino acids, depends solely on mother-to-embryo transport through it. However, the molecular mechanisms underlying this amino acid supply are poorly understood. In this study, we focused on system A amino acid transporters /SNAT1, /SNAT2, and /SNAT4, which carry neutral, short-side-chain amino acids, to determine their involvement in placental or embryonic development. A triple-target CRISPR screen identified /SNAT4 as the critical amino acid transporter for placental development in mice. We established mouse lines from the CRISPR founders with large deletions in and found that, consistent with the imprinted paternal expression of /SNAT4 in the placenta, paternal knockout (KO) but not maternal KO of /SNAT4 caused placental hypoplasia associated with reduced fetal weight. Immunostaining revealed that SNAT4 was widely expressed in differentiating cytotrophoblasts and maturing trophoblasts at the maternal-fetal interface. A blood metabolome analysis revealed that amino acid concentrations were globally reduced in /SNAT4 mutant embryos. These results indicated that SNAT4-mediated amino acid transport in mice plays a major role in placental and embryonic development. Given that expression of in the placenta is conserved in other species, our /SNAT4 mutant mice could be a promising model for the analysis of placental defects leading to intrauterine growth restriction in mammals.