title: Deep phylogenomics of a tandem-repeat galectin regulating appendicular skeletal pattern formation.
abstract: A multiscale network of two galectins Galectin-1 (Gal-1) and Galectin-8 (Gal-8) patterns the avian limb skeleton. Among vertebrates with paired appendages, chondrichthyan fins typically have one or more cartilage plates and many repeating parallel endoskeletal elements, actinopterygian fins have more varied patterns of nodules, bars and plates, while tetrapod limbs exhibit tandem arrays of few, proximodistally increasing numbers of elements. We applied a comparative genomic and protein evolution approach to understand the origin of the galectin patterning network. Having previously observed a phylogenetic constraint on Gal-1 structure across vertebrates, we asked whether evolutionary changes of Gal-8 could have critically contributed to the origin of the tetrapod pattern.
  
  
  
  Translocations, duplications, and losses of Gal-8 genes in Actinopterygii established them in different genomic locations from those that the Sarcopterygii (including the tetrapods) share with chondrichthyans. The sarcopterygian Gal-8 genes acquired a potentially regulatory non-coding motif and underwent purifying selection. The actinopterygian Gal-8 genes, in contrast, did not acquire the non-coding motif and underwent positive selection.
  
  
  
  These observations interpreted through the lens of a reaction-diffusion-adhesion model based on avian experimental findings can account for the distinct endoskeletal patterns of cartilaginous, ray-finned, and lobe-finned fishes, and the stereotypical limb skeletons of tetrapods.
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. ramray@mrdg.iisc.ernet.in.|Present Address: Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore, 560012, India. ramray@mrdg.iisc.ernet.in.
authors.forename: Ramray
authors.initials: R
authors.lastname: Bhat
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, 92697, USA.
authors.forename: Mahul
authors.initials: M
authors.lastname: Chakraborty
authors.affiliation: Department of Mathematics, Western Washington University, Bellingham, WA, 98229, USA.
authors.forename: Tilmann
authors.initials: T
authors.lastname: Glimm
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, 06520, USA.|Minnesota Center for Philosophy of Science, University of Minnesota, Minneapolis, MN, 55455, USA.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Stewart
authors.affiliation: Department of Cell Biology and Anatomy, New York Medical College, Valhalla, NY, 10595, USA. newman@nymc.edu.
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Newman
mesh_terms: D000818:Animals; D005075:Biological Evolution; D019143:Evolution, Molecular; D029941:Fish Proteins / Q000235:genetics*; D005399:Fishes / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics; D037161:Galectins / Q000235:genetics*; D023281:Genomics; D009024:Morphogenesis; D010802:Phylogeny; D012863:Skeleton / Q000033:anatomy & histology*; D020080:Tandem Repeat Sequences; D014714:Vertebrates / Q000033:anatomy & histology* / Q000145:classification / Q000235:genetics*
chemical_list: D029941:Fish Proteins; D037161:Galectins
keywords: Galectin-8; Homology; Limb skeleton; Mathematical modeling; Pattern formation; Phylogeny