Restriction factor required to restrict infectivity of gammaretroviruses: acts by inhibiting early step of viral infection and impairing the ability of the viral particle to translocate its content to the cytoplasm (By similarity). Enhances the incorporation of serine into phosphatidylserine and sphingolipids. May play a role in providing serine molecules for the formation of myelin glycosphingolipids in oligodendrocytes. Localizes to the cell membrane, where it is efficiently incorporated into budding gammaretrovirus virions and impairs subsequent virion penetration of susceptible target cells. Brain. Expressed at high levels in the white matter and the oligodendroglial cells of the brain. Expressed at low levels in the liver. First detected in significant amounts at postnatal day 2 (P2) and increases about twofold to a peak value at P17-P20 and declines significantly thereafter. Up-regulated during the differentiation of oligodendrocyte lineage cells and during brain development at the time of myelination. Down-regulated in the hippocampal CA fields and dentate gyrus by seizures. Belongs to the TDE1 family.