The Xiphophorus maculatus Genome Project

The genus Xiphophorus comprises 27 recognized species of live-bearing fishes that populate freshwater habitats in the slopes of the Sierra Madre uplifts of Mexico, and extending into Guatemala, Belize, and Honduras. In native habitats, combinations of spatial, ecological, behavioral, and anatomic factors discourage cross-species mating, such that naturally occurring interspecific Xiphophorus hybrids are virtually unknown. In the laboratory, however, most members of the genus are inter-fertile with one another and produce fertile offspring. Experimental crossing of many different species have revealed a diversity of developmental perturbations influencing the regulation of pigmentation patterns and intensity, growth and maturation rates, behavioral patterns, alternative sex determination mechanisms, and susceptibilities to spontaneous or induced neoplasias. Consequently, the Xiphophorus species genetic system represents an easily manipulated and astoundingly diverse model system for examining the evolution of interacting gene complexes and for dissecting the genetic bases of developmental programs, behaviors, and the molecular processes underlying neoplastic initiation and progression.

The X. maculatus genome sequence is derived from a single highly inbred (104th generation) adult female fish from the Xiphophorus Genetic Stock Center. This genome sequence enables comparisons of gene content and structure implicated in the regulation of complex traits identified in interspecific hybrid crosses. In addition, the availability of Xiphophorus sequence will allow investigators to take advantage of the extensive genomic resources of the pufferfish (Fugu rubripes), zebrafish (Danio rerio), and medaka (Oryzias latipes) to predict the genomic structures and identification of factors associated with interesting complex traits, thereby facilitating the discovery of candidate genes for further study.

The genomes listed below have been analyzed by the PHRINGE ("Phylogenetic Resources for the Interpretation of Genomes") pipeline. Briefly described, PHRINGE creates a graph with all inferred protein sequences as nodes, with edges formed from distance scores calculated from their full length alignments, then clusters these into gene families using a method that considers the evolutionary relationships among the organisms, then performs a phylogenetic analysis on each. This allows the most accurate possible assignment of orthologous and paralogous relationships, inference of retained gene function, and reconstruction of gene duplications and losses. Users can see the multiple sequence alignments and phylogenetic trees of all genes, compare intron-exon structures, and see the relative arrangements of homologs across all genomes. See a summary of the PHRINGE method, details of the PHRINGE pipeline, or an explanation of why it is important to use evolutionary analysis to find orthologs.

This project is being led by Professor Ronald Walter of Texas State University San Marcos and Manfred Schartl of the University of Wurzburg . Credit for informatics work and database design and construction goes to Bob Stiles of Roundtrip Networks, Wayne Huang of Linear Time, and Asoke Talukder of Geschickten.