title: Robertsonian chromosomes and the nuclear architecture of mouse meiotic prophase spermatocytes.
abstract: BACKGROUND
  The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains from different bivalents. The meiotic nuclear architecture depends on the chromosome characteristics and consequently is prone to modification by chromosomal rearrangements. In this work, we consider Mus domesticus spermatocytes with diploid chromosome number 2n = 40, all telocentric, and investigate a possible modification of the ancestral nuclear architecture due to the emergence of derived Rb chromosomes, which may be present in the homozygous or heterozygous condition.
  
  
  RESULTS
  In the 2n = 40 spermatocyte nuclei random associations mediated by pericentromeric heterochromatin among the 19 telocentric bivalents ocurr at the nuclear periphery. The observed frequency of associations among them, made distinguishable by specific probes and FISH, seems to be the same for pairs that may or may not form Rb chromosomes. In the homozygote Rb 2n = 24 spermatocytes, associations also mediated by pericentromeric heterochromatin occur mainly between the three telocentric or the eight metacentric bivalents themselves. In heterozygote Rb 2n = 32 spermatocytes all heterochromatin is localized at the nuclear periphery, yet associations are mainly observed among the three telocentric bivalents and between the asynaptic axes of the trivalents.
  
  
  CONCLUSIONS
  The Rb chromosomes pose sharp restrictions for interactions in the 2n = 24 and 2n = 32 spermatocytes, as compared to the ample possibilities for interactions between bivalents in the 2n = 40 spermatocytes. Undoubtedly the emergence of Rb chromosomes changes the ancestral nuclear architecture of 2n = 40 spermatocytes since they establish new types of interactions among chromosomal domains, particularly through centromeric and heterochromatic regions at the nuclear periphery among telocentric and at the nuclear center among Rb metacentric ones.
authors.forename: Soledad
authors.initials: S
authors.lastname: Berríos
authors.forename: Catalina
authors.initials: C
authors.lastname: Manieu
authors.forename: Julio
authors.initials: J
authors.lastname: López-Fenner
authors.forename: Eliana
authors.initials: E
authors.lastname: Ayarza
authors.forename: Jesús
authors.initials: J
authors.lastname: Page
authors.forename: Marisel
authors.initials: M
authors.lastname: González
authors.forename: Marcia
authors.initials: M
authors.lastname: Manterola
authors.forename: Raúl
authors.initials: R
authors.lastname: Fernández-Donoso
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000000981:diagnostic imaging / Q000235:genetics*; D033481:Chromosomes, Mammalian / Q000648:ultrastructure*; D006570:Heterochromatin; D006579:Heterozygote; D006720:Homozygote; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D049469:Meiotic Prophase I; D051379:Mice; D015335:Molecular Probes; D049471:Pachytene Stage; D013090:Spermatocytes / Q000648:ultrastructure*; D013347:Subcellular Fractions; D014463:Ultrasonography
chemical_list: D006570:Heterochromatin; D015335:Molecular Probes