Seroussi, E., Department of Animal Science, Agricultural Research Organization, Volcani Center, P.O. Box 15159, Rishon LeTsiyon, Israel
Pitel, F., Université de Toulouse, INRA, INPT, ENVT, GenPhySE, Castanet Tolosan, France
Leroux, S., Université de Toulouse, INRA, INPT, ENVT, GenPhySE, Castanet Tolosan, France
Morisson, M., Université de Toulouse, INRA, INPT, ENVT, GenPhySE, Castanet Tolosan, France
Bornelöv, S., Uppsala University, Department of Medical Biochemistry and Microbiology, Uppsala, Sweden
Miyara, S., Department of Animal Science, Agricultural Research Organization, Volcani Center, P.O. Box 15159, Rishon LeTsiyon, Israel
Yosefi, S., Department of Animal Science, Agricultural Research Organization, Volcani Center, P.O. Box 15159, Rishon LeTsiyon, Israel
Cogburn, L.A., University of Delaware, Department of Animal and Food Sciences, Newark, United States
Burt, D.W., University of Edinburgh, The Roslin Institute and Royal (Dick) School of Veterinary Studies, Midlothian, United Kingdom
Anderson, L., Uppsala University, Department of Medical Biochemistry and Microbiology, Uppsala, Sweden, Texas A and M University, Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, College Station, TX, United States, Swedish University of Agricultural Sciences, Department of Animal Breeding and Genetics, Uppsala, Sweden
Friedman-Einat, M., Department of Animal Science, Agricultural Research Organization, Volcani Center, P.O. Box 15159, Rishon LeTsiyon, Israel

Background: Misidentification of the chicken leptin gene has hampered research of leptin signaling in this species for almost two decades. Recently, the genuine leptin gene with a GC-rich (~70%) repetitive-sequence content was identified in the chicken genome but without indicating its genomic position. This suggests that such GC-rich sequences are difficult to sequence and therefore substantial regions are missing from the current chicken genome assembly. Results: A radiation hybrid panel of chicken-hamster Wg3hCl2 cells was used to map the genome location of the chicken leptin gene. Contrary to our expectations, based on comparative genome mapping and sequence characteristics, the chicken leptin was not located on a microchromosome, which are known to contain GC-rich and repetitive regions, but at the distal tip of the largest chromosome (1p). Following conserved synteny with other vertebrates, we also mapped five additional genes to this genomic region (ARF5, SND1, LRRC4, RBM28, and FLNC), bridging the genomic gap in the current Galgal5 build for this chromosome region. All of the short scaffolds containing these genes were found to consist of GC-rich (54 to 65%) sequences comparing to the average GC-content of 40% on chromosome 1. In this syntenic group, the RNA-binding protein 28 (RBM28) was in closest proximity to leptin. We deduced the full-length of the RBM28 cDNA sequence and profiled its expression patterns detecting a negative correlation (R = - 0.7) between the expression of leptin and of RBM28 across tissues that expressed at least one of the genes above the average level. This observation suggested a local regulatory interaction between these genes. In adipose tissues, we observed a significant increase in RBM28 mRNA expression in breeds with lean phenotypes. Conclusion: Mapping chicken leptin together with a cluster of five syntenic genes provided the final proof for its identification as the true chicken ortholog. The high GC-content observed for the chicken leptin syntenic group suggests that other similar clusters of genes in GC-rich genomic regions are missing from the current genome assembly (Galgal5), which should be resolved in future assemblies of the chicken genome. © 2017 The Author(s).