Exceptional conservation of horse–human gene order on X chromosome revealed by high-resolution radiation hybrid mapping

Abstract

Development of a dense map of the horse genome is key to efforts aimed at identifying genes controlling health, reproduction, and performance. We herein report a high-resolution gene map of the horse (Equus caballus) X chromosome (ECAX) generated by developing and typing 116 gene-specific and 12 short tandem repeat markers on the 5,000-rad horse ؋ hamster whole-genome radiation hybrid panel and mapping 29 gene loci by fluorescence in situ hybridization. The human X chromosome sequence was used as a template to select genes at 1-Mb intervals to develop equine orthologs. Coupled with our previous data, the new map comprises a total of 175 markers (139 genes and 36 short tandem repeats, of which 53 are fluorescence in situ hybridization mapped) distributed on average at Ϸ880-kb intervals along the chromosome. This is the densest and most uniformly distributed chromosomal map presently available in any mammalian species other than humans and rodents. Comparison of the horse and human X chromosome maps shows remarkable conservation of gene order along the entire span of the chromosomes, including the location of the centromere. An overview of the status of the horse map in relation to mouse, livestock, and companion animal species is also provided. The map will be instrumental for analysis of X linked health and fertility traits in horses by facilitating identification of targeted chromosomal regions for isolation of polymorphic markers, building bacterial artificial chromosome contigs, or sequencing.gene mapping ͉ comparative map ͉ mouse

Rapid divergence and expansion of the X chromosome in papaya

“…In mammals, the gene order in the X chromosomes has been conserved across such distantly related species as human, cat, horse, cattle, and elephant, with the exception of mouse (22)(23)(24)(25)(26). In the human X and chicken Z, gene trafficking and sequence expansion have been detected, using comparisons with orthologous autosomal segments of other species (12)(13)(14).…”

Genetic Mapping in a Natural Population of Collared Flycatchers (Ficedula albicollis): Conserved Synteny but Gene Order Rearrangements on the Avian Z Chromosome

“…Moreover, by focusing on the organization of the Z chromosome, we can address the degree of sex chromosome conservation in a system of female heterogamety. The latter is motivated by the fact that while there have been numerous interchromosomal rearrangements among autosomes during mammalian evolution (Murphy et al 2005), the gene content of the X chromosome is largely conserved across all eutherian lineages (Murphy et al 1999;Raudsepp et al 2004). Is this a consequence of the mode of dosage compensation in mammals or is it a general feature of sex chromosome evolution?…”

The Birds and the Bees and the Flowers and the Trees: Lessons from Genetic Mapping of Sex Determination in Plants and Animals

“…Most therian mammals have XY GSD, and the X has changed very little since the addition, 166 million years ago, of the q arm of the current placental X to the ancestral therian X, which remains the marsupial X (Waters et al 2001). The gene content and gene order of the therian X chromosome have changed little (Murphy et al 1999;Raudsepp et al 2004;Delgado et al 2009), apart from duplications of genes onto the X and movements of some genes off the X (Potrzebowski et al 2009), and formation of neo-sex chromosomes in some species (reviewed in Bakloushinskaya 2009). The avian Z chromosome gene content and order are even more conserved (Dawson et al 2007;Backström et al 2008).…”