DEFECTIVE FOREBRAIN DEVELOPMENT IN MICE LACKING GP330 MEGALIN/

gp330/megalin, a member of the low density lipoprotein (LDL) receptor gene family, is expressed on the apical surfaces of epithelial tissues , including the neuroepithelium, where it mediates the endocytic uptak e of diverse macromolecules, such as cholesterol-carrying lipoproteins , proteases, and antiproteinases. Megalin knockout mice manifest abnor malities in epithelial tissues including lung and kidney that normally express the protein and they die perinatally from respiratory insuffi ciency. In brain, impaired proliferation of neuroepithelium produces a holoprosencephalic syndrome, characterized by lack of olfactory bulbs , forebrain fusion, and a common ventricular system, Similar syndromes in humans and animals are caused by insufficient supply of cholestero l during development, Because megalin can bind lipoproteins, we propos e that the receptor is part of the maternal-fetal lipoprotein transpor t system and mediates the endocytic uptake of essential nutrients in t he postgastrulation stage.