06-P015 Increased dosage of Sox3 leads to Subcommissural Organ hypoplasia and is associated with Congenital Hydrocephalus

the foregut endoderm and the defective expansion of the midand hindgut at early somite stages. However, there remains unclear whether or not Sox17 is required for the subsequent development, maturation and maintenance of the endoderm derivatives such as livers and pancreas due to the early embryonic lethal of Sox17-null mutant embryos before 10.0 dpc. Recently, we noticed the neonatal lethality of Sox17 heterozygous pups which were back-crossed against C57BL/6 mice. Pathological analyses revealed that a reduced Sox17 activity clearly leads to the defective maintenance of fetal liver development from 16.5 dpc. Molecular marker analyses also demonstrated the ER-stress induction in the hepatocytes, leading the defective maintenance of Hnf4alpha expression the fetal hepatocyte of the Sox17 heterozygous embryos. This is clearly in contrast to their proper vascularization and hematopoiesis in the defective Sox17 heterozygous livers at 16.0–17.5 dpc. In this meeting, we will discuss the possible roles of Sox17 in the maintenance of the fetal liver development/maturation on the basis of the liver transcriptome data revealed by the microarray analyses.