Molecular and cytogenetic characterization of the mouse ATP-binding cassette transporter Abcg4

We have cloned a new mouse ATP-binding cassette (ABC) transporter, Abcg4, from a complementary DNA (cDNA) library of mouse brain. The cloned Abcg4 cDNA encodes a protein consisting of 646 amino acids and including one ATP-binding cassette and six transmembrane domains. The Abcg4 protein exhibits high identity (96%) with human ABCG4 in terms of the amino acid sequence. Fluorescence in situ hybridization with mouse and rat chromosomes has revealed that the Abcg4 gene is located on chromosomes 9A5.3 and 8q22 distal in mouse and rat, respectively. In these loci on mouse and rat chromosomes, conserved linkage homologies were hitherto identified with human chromosome 11q23, which involves the human ABCG4 gene. The mouse Abcg4 gene as well as the human ABCG4 gene each has a total of 14 exons to encode its respective protein. High transcript levels of mouse Abcg4 were detected in mouse brain, spleen, eye, and bone marrow. Taken together, our data on the chromosomal location, gene homology, protein structure, and phylogenetic relationships strongly support the idea that mouse Abcg4 is orthologue to the human ABCG4. By functionally analyzing the mouse Abcg4 protein, we may better understand the biological role of the human ABCG4 transporter.