The Nedd4 gene was initially identified by a subtraction cloning approach as a highly expressed transcript in the mouse embryonic brain. Cloning of the Nedd4 cDNA indicated that it can encode a protein of approximately 103 kDa, consisting of a Ca2+ and phospholipid binding domain, three putative protein-protein interaction domains (the WW domains), and a carboxyl-terminus region similar to the ubiquitin-protein ligase domain (hect domain). In mouse embryos, the expression of Nedd4 in the central nervous system is highest during neurogenesis and decreases as development progresses. In addition to the central nervous system, the expression of Nedd4 is detected in various embryonic tissues and persists in most adult tissues. Using an antibody raised against a fusion protein, we show that Nedd4 protein is localized to the cellular cytoplasm. We have mapped the mouse Nedd4 gene to chromosome 9 using an interspecific backcross panel. Nedd4 maps to a previously defined homologous region between human and mouse chromosomes and thus provides additional information regarding interspecies comparative mapping.