Exon 1 and 3.6Kb of intron 1 were replaced by a minigene construct encoding amino acids 4448-4661 of the mouse Lrp2 (megalin) polypeptide (NM_001081088) and stop codon fused to 3 copies of the flag epitope at the amino terminus. A neo resistance cassette immediately follows the megalin intracellular domain (ICD) construct. Western blot analysis confirmed cytosolic expression of the ICD form in kidneys but not the wild-type product.