A standardized nomenclature for the mouse and rat prolactin superfamilies Michael J. Soares, 1 S. M. Khorshed Alam, 1 Mary Lynn Duckworth, 2 Nelson D. Horseman, 3 Toshihiro Konno, 1 Daniel I. H. Linzer, 4 Lois J. Maltais, 5 Marit Nilsen-Hamilton, 6 Kunio Shiota, 7 Jennifer R. Smith, 8 Michael Wallis 9 1 Institute of Maternal-Fetal Biology, University of Kansas Medical Center, Kansas City, Kansas, 66160, USA 2 Department of Physiology, University of Manitoba, R3E 3J7, Winnipeg, Manitoba, Canada 3 Department of Molecular and Cellular Physiology, University of Cincinnati, Cincinnati, Ohio, 45267, USA 4 Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois, 60208, USA 5 Mouse Genome Informatics Resource and Mouse Genomic Nomenclature Committee, The Jackson Laboratory, Bar Harbor, Maine, 04609, USA 6 Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, 50011, USA 7 Department of Cellular Biochemistry, Veterinary Medical Sciences/Animal Resource Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku Tokyo, Japan 8 Rat Genome Database, Medical College of Wisconsin, Milwaukee, Wisconsin, 53226, USA 9 Biochemistry Department, School of Life Sciences, University of Sussex, Brighton, BN1 9QG, UK Received: 22 January 2007 / Accepted: 29 January 2007 The prolactin (PRL) locus has undergone species- specific expansions. These expansions are most notable in the mouse, rat, and cow (Soares 2004). In the mouse, the PRL locus spans 1 Mb on Chromo- some 13 and includes 23 known genes (Wiemers et al. 2003; Mallon et al. 2004), whereas the rat PRL locus spans 1.7 Mb on Chromosome 17 and includes 24 known genes (Alam et al. 2006). The two loci are mostly orthologous but do exhibit some differences. Previous nomenclature for the mouse and rat PRL superfamilies is awkward. Names were originally assigned based on biological activities [placental lac- togen (PL) and chorionic somatomammotropin (CS); proliferin (PLF)] and on structural similarities to PRL or PLF [PRL-related protein (PRP); PRL-like protein (PLP); PLF-related protein (PLF-RP)]. As the mouse and rat genome databases were established, some improvements were made in the nomenclature but it has remained cumbersome. The previous nomencla- ture was also confusing when comparisons were made across species. Terms such as CS, PL, and PRP have been used to describe members of the PRL and growth hormone families of other species, including the human and cow. Human CSs and PLs and bovine PLs and PRPs are not orthologous with CSs, PLs, and PRPs of the mouse and rat. A standardized nomenclature has been devel- oped in conjunction with staff at the Mouse Genome Informatics (MGI, http://www.informatics.jax.org) and Rat Genome Database (RGD, http:// www.rgd.mcw.edu/). The nomenclature is based on structural relatedness of members of the mouse and rat PRL superfamilies (Table 1, Fig. 1). It is expected that this new standardized nomenclature will pro- vide a logical framework for the naming of new members of the PRL superfamily as they are dis- covered, including new orthologs and paralogs from other species. A couple of comments about the new nomen- clature are required. The family and subfamily des- ignations are ordered based on multiple sequence analysis (Thompson et al. 1997) and phylogenetic tree construction (Page 1996) using mouse and rat PRL family sequences. If PRL family sequences from other species are included in the analysis, then the ordering of the families and subfamilies exhibit dif- ferences (Alam et al. 2006). Consequently, it is important to appreciate that the phylogenetic tree used for development of the new nomenclature may not represent a true phylogeny. Nevertheless, the mouse and rat PRL family tree (Fig. 1) is the best currently available. Correspondence to: Michael J. Soares, Institute of Maternal-Fetal Biology, Division of Cancer and Developmental Biology, Depart- ment of Pathology and Laboratory Medicine, University of Kansas Medical Center, Kansas City, KS 66160, USA; E-mail: msoares@ kumc.edu 154 DOI: 10.1007/s00335-007-9003-y  Volume 18, 154156 (2007)  Ó Springer Science+Business Media, LLC 2007 Letter