Publication

Physical mapping and refinement of the painted turtle genome (Chrysemys picta) inform amniote genome evolution and challenges turtle-bird chromosomal conservation.

Genome Biol Evol. 2015 Jun 24. pii: evv119. [Epub ahead of print]

Abstract

Comparative genomics continues illuminating amniote genome evolution, but for many lineages our understanding remains incomplete. Here we refine the assembly (CPI 3.0.3 NCBI AHGY00000000.2) and develop a cytogenetic map of the painted turtle (Chrysemys picta - CPI) genome, the first in turtles and in vertebrates with temperature-dependent sex determination. A comparison of turtle genomes with those of chicken, selected non-avian reptiles and human revealed shared and novel genomic features, such as numerous chromosomal rearrangements. The largest conserved syntenic blocks between birds and turtles exist in four macrochromosomes, whereas rearrangements were evident in these and other chromosomes, disproving that turtles and birds retain fully conserved macrochromosomes for >300 million years. C-banding revealed large heterochromatic blocks in the centromeric region of only few chromosomes. The nucleolar-organizing region (NOR) mapped to a single CPI microchromosome, whereas in some turtles and lizards the NOR maps to non-homologous sex-chromosomes, thus revealing independent translocations of the NOR in various reptilian lineages. There was no evidence for recent chromosomal fusions as interstitial telomeric-DNA was absent. Some repeat elements (CR1-like, Gypsy) were enriched in the centromeres of five chromosomes, whereas others were widespread in the CPI genome. BAC clones were hybridized to 18 of the 25 CPI chromosomes and anchored to a G-banded ideogram. Several CPI sex-determining genes mapped to five chromosomes, and homology was detected between yet other CPI autosomes and the globally non-homologous sex chromosomes of chicken, other turtles and squamates; underscoring the independent evolution of vertebrate sex-determining mechanisms.

Authors

Badenhorst D, Hillier LW, Literman R, Montiel EE, Radhakrishnan S, Shen Y, Minx P, Janes D, Warren WC, Edwards SV, Valenzuela N.

Institute Authors

Patrick Minx, Wes Warren, Ph.D.