Changes of nuclear membrane lipid composition affect RNA nucleocytoplasmictransport

We have previously shown that the nuclear membrane fluidity of rat liver, m easured by fluorescence anisotropy of two probes, is higher in the hydropho bic core, with respect to the bilayer surface, in newborn rats compared to adult rats. The aim of the present research is to investigate whether the n uclear membrane fluidity influences RNA nucleocytoplasmic transport. To thi s end two experimental models were used: the fluidity of nuclear membrane i solated from adult rats was increased by a choline base exchange reaction, which is known to be accompanied by an increase of phosphatidylcholine unsa turated fatty acids, whereas that of nuclear membrane isolated from newborn rats was decreased by incubation with dimyristoylphosphatidylcholine-chole sterol liposomes. The RNA efflux, evaluated by using [H-3]uridine, signific antly increased in the adult nuclear membrane submitted to choline base exc hange reaction, whereas a strong decrease in the newborn nuclear membrane e nriched with cholesterol was found. The activity of nucleoside triphosphata se, a nuclear membrane-associated enzyme which is correlated with mRNA tran sport, showed parallel variations. Therefore, for the first time, we have p rovided evidence that the nuclear membrane fluidity plays a regulatory role in RNA nucleocytoplasmic transport, although the mechanism by which this e ffect takes place remains to be clarified. (C) 1999 Academic Press.