title: Comparative analysis of chicken chromosome 28 provides new clues to the evolutionary fragility of gene-rich vertebrate regions.
abstract: The chicken genome draft sequence has provided a valuable resource for studies of an important agricultural and experimental model species and an important data set for comparative analysis. However, some of the most gene-rich segments are missing from chicken genome draft assemblies, limiting the analysis of a substantial number of genes and preventing a closer look at regions that are especially prone to syntenic rearrangements. To facilitate the functional and evolutionary analysis of one especially gene-rich, rearrangement-prone genomic region, we analyzed sequence from BAC clones spanning chicken microchromosome GGA28; as a complement we also analyzed a gene-sparse, stable region from GGA11. In these two regions we documented the conservation and lineage-specific gain and loss of protein-coding genes and precisely mapped the locations of 31 major human-chicken syntenic breakpoints. Altogether, we identified 72 lineage-specific genes, many of which are found at or near syntenic breaks, implicating evolutionary breakpoint regions as major sites of genetic innovation and change. Twenty-two of the 31 breakpoint regions have been reused repeatedly as rearrangement breakpoints in vertebrate evolution. Compared with stable GC-matched regions, GGA28 is highly enriched in CpG islands, as are break-prone intervals identified elsewhere in the chicken genome; evolutionary breakpoints are further enriched in GC content and CpG islands, highlighting a potential role for these features in genome instability. These data support the hypothesis that chromosome rearrangements have not occurred randomly over the course of vertebrate evolution but are focused preferentially within "fragile" regions with unusual DNA sequence characteristics.
authors.affiliation: Genome Biology Group, Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: Laurie
authors.initials: L
authors.lastname: Gordon
authors.forename: Shan
authors.initials: S
authors.lastname: Yang
authors.forename: Mary
authors.initials: M
authors.lastname: Tran-Gyamfi
authors.forename: Dan
authors.initials: D
authors.lastname: Baggott
authors.forename: Mari
authors.initials: M
authors.lastname: Christensen
authors.forename: Aaron
authors.initials: A
authors.lastname: Hamilton
authors.forename: Richard
authors.initials: R
authors.lastname: Crooijmans
authors.forename: Martien
authors.initials: M
authors.lastname: Groenen
authors.forename: Susan
authors.initials: S
authors.lastname: Lucas
authors.forename: Ivan
authors.initials: I
authors.lastname: Ovcharenko
authors.forename: Lisa
authors.initials: L
authors.lastname: Stubbs
mesh_terms: D000818:Animals; D002645:Chickens / Q000235:genetics*; D019457:Chromosome Breakage; D002874:Chromosome Mapping; D002875:Chromosomes; D019143:Evolution, Molecular; D020440:Gene Duplication; D015321:Gene Rearrangement; D015894:Genome, Human; D006801:Humans; D051379:Mice; D008957:Models, Genetic; D013045:Species Specificity; D026801:Synteny