Genomic characterization of multiple leptin genes and a leptin receptor gene in the Japanese medaka, Oryzias latipes.

We comprehensively surveyed leptin (LEP) and leptin receptor (LEPR) genes in medaka, Oryzias latipes and identified two LEP (mLEP-A and mLEP-B) genes and one LEPR (mLEPR) gene. The gene arrangement around both mLEPs in medaka chromosomes 6 and 23 were well conserved with human chromosome 7q31 including LEP. This means that both mLEP-A and mLEP-B are orthologs of human LEP and paralogs derived from whole-genome duplication early in the teleost lineage. The expression of mLEP-A mRNA was relatively high in the liver, and mLEP-B was expressed in the brain and eye. The 3-D modeling of both mLEP-A and mLEP-B protein showed conservation of the four-helix structure that is characteristic in vertebrate leptin. Human LEPR and leptin receptor overlapping the transcript (LEPROT) genes are continuously located on chromosome 1p31. In contrast, medaka LEPR and LEPROT are located on chromosomes 4 and 17, respectively, but both genomic regions showed genomic synteny with the human genome around the LEPR on chromosome 1p31. This result could mean that the medaka chromosome regions around the LEPR and LEPROT are paralogous genomic regions derived from whole-genome duplication, and that the overlapping gene of LEPR and LEPROT was subsequently lost in the medaka genome.