title: Architecture and organization of chicken microchromosome 16: order of the NOR, MHC-Y, and MHC-B subregions.
abstract: Here we present a high-resolution cytogenomic analysis of chicken microchromosome 16. We established the location of the major histocompatibility complex (MHC)-B and -Y subregions relative to each other and to the nucleolus organizer region (NOR) encoding the 18S-5.8S-28S ribosomal DNA. To do so, we employed multicolor fluorescence in situ hybridization using large-insert bacterial artificial chromosome clones with fully sequenced inserts or repetitive sequence probes specific for the subregion of interest. We show that the MHC-Y and -B regions are located on the same side of the NOR, rather than opposite ends, as previously proposed. On the q arm, the MHC-Y is closely adjacent to the NOR, whereas the MHC-B is distal near the q-terminus. A relatively large GC-rich region separates the 2 MHC subregions and includes a specialized structure, a secondary constriction. We propose that the GC-rich large physical distance is the basis for the lack of genetic linkage between the NOR and MHC-B and between the MHC-Y and -B. An integrated model for GGA 16 is presented that incorporates gene complex order in the context of key architectural features including p and q arms, primary (centromere) and secondary constrictions, telomeres, as well as AT- and GC-rich regions.
authors.affiliation: Department of Animal Science, University of California, Davis, CA 95616, USA. medelany@ucdavis.edu
authors.forename: Mary E
authors.initials: ME
authors.lastname: Delany
authors.forename: Charmaine M
authors.initials: CM
authors.lastname: Robinson
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Goto
authors.forename: Marcia M
authors.initials: MM
authors.lastname: Miller
mesh_terms: D000818:Animals; D002645:Chickens / Q000235:genetics*; D002874:Chromosome Mapping / Q000379:methods*; D002875:Chromosomes; D017404:In Situ Hybridization, Fluorescence; D008285:Major Histocompatibility Complex / Q000235:genetics*; D009697:Nucleolus Organizer Region / Q000235:genetics*