MO-1 is a newly identified gene and gene product associated with morbid obesity. Isolated MO-1 nucleic acids, MO-1 polypeptides, oligonucleotides that hybridize to MO-1 nucleic adds, and vectors, including expression vectors, comprising MO-1 nucleic acids are disclosed, as are isolated host cells, antibodies, transgenic non-human animals, compositions, and kits relating to MO-1. Methods of detecting the presence of MO-1 nucleic acid, screening for agents which affect MO-1 activity, and screening for MO-1 variants are also disclosed.