Overlapping expression patterns of the multiligand endocytic receptors cubilin and megalin in the CNS, sensory organs and developing epithelia of the rodent embryo.

Cubilin and megalin are multiligand epithelial endocytic receptors well characterized in the adult kidney and ileum where they form a complex essential for protein, lipid and vitamin uptake. Although inactivation of the megalin gene leads to holoprosencephaly and administration of anti-cubilin antibodies induces fetal resorptions or cranio-facial malformations their function in the developing embryo remains unclear. We recently showed that both proteins are strongly expressed by the maternal-fetal interfaces and the neuroepithelium of the early rodent embryo where they co-localize and form a complex important for nutrient uptake. The aim of the present study was the further investigation of cubilin expression at later developmental stages of the rodent embryo and its correlation to that of megalin. Immunohistochemical and in situ hybridization analysis showed striking similarities in the spatial and temporal expression patterns of cubilin and megalin. The electrophoretic mobility of both proteins was identical to that of the adult as revealed by Western blot analysis. Cubilin and megalin were strongly expressed in the sensory organs, the central nervous system, the respiratory and urogenital tracts as well as in the thymus, parathyroids and thyroid. In each site, the expression mainly concerned epithelial structures and correlated with the onset of epithelial induction. Depending on the site, a decreased or restricted expression was observed by the end of the gestation for both proteins.