Mouse melanoma growth stimulatory activity gene (Mgsa) is polymorphic and syntenic with the W, patch, rumpwhite, and recessive spotting loci on chromosome 5.

Melanoma growth stimulatory activity (Mgsa) is a polypeptide growth factor originally detected in culture medium of the human malignant melanoma cell line Hs294T and may have an autocrine role in neoplastic growth. Mgsa is a member of the small inducible gene (SIG) family and shares homology with beta-thromboglobulin and platelet factor 4. Mgsa was localized to chromosome 5 using a cDNA probe for mouse Mgsa and somatic cell hybrids and is thus syntenic with Kit (W), Ph, Rw, and rs loci. The results eliminate Mgsa as the product of the Steel locus on chromosome 10, but raise the possibility that Mgsa might be synonymous with a chromosome 5 locus affecting skin pigmentation.