Conditional deletions refine the embryonic requirement for Dlk1

► Dlk1flox mice were generated to allow conditional deletion of the Dlk1 gene. ► Dlk1cons null mutants display perinatal death and reduced growth of survivors. ► Increased cellularity of Dlk1cons placentae may limit maternal-fetal exchange. ► Loss of Dlk1 in beta cells, somatotropes or endothelial cells causes no pathology.