title: Nucleolar dominance and maternal control of 45S rDNA expression.
abstract: Using a system of interspecies hybrids, trihybrids, and recombinants with varying proportions of genomes from three distinct Xenopus species, we provide evidence for de novo epigenetic silencing of paternal 45 S ribosomal ribonucleic acid (rRNA) genes and their species-dependent expression dominance that escapes transcriptional inactivation after homologous recombination. The same pattern of imprinting is maintained in the offspring from mothers being genetic males (ZZ) sex-reversed to females, indicating that maternal control of ribosomal deoxyribonucleic acid (rDNA) expression is not sex-chromosome linked. Nucleolar dominance (nucleolus underdevelopment) in Xenopus hybrids appears to be associated with a major non-Mendelian reduction in the number of 45 S rDNA gene copies rather than a specific pattern of their expression. The loss of rRNA gene copies in F1 hybrids was non-random with respect to the parental species, with the transcriptionally dominant variant preferentially removed from hybrid zygotes. This dramatic disruption in the structure and function of 45 S rDNA impacts transcriptome patterns of small nucleolar RNAs and messenger RNAs, with genes from the ribosome and oxidative stress pathways being among the most affected. Unorthodoxies of rDNA inheritance and expression may be interpreted as hallmarks of genetic conflicts between parental genomes, as well as defensive epigenetic mechanisms employed to restore genome integrity.
authors.affiliation: Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Michalak
authors.affiliation: Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA Institute of Biology, University of Bialystok, PL-15-245, Poland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Maciak
authors.affiliation: Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Young Bun
authors.initials: YB
authors.lastname: Kim
authors.affiliation: Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Graciela
authors.initials: G
authors.lastname: Santopietro
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
authors.forename: Jung Hun
authors.initials: JH
authors.lastname: Oh
authors.affiliation: Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Kang
authors.affiliation: The Edward Via College of Osteopathic Medicine, Blacksburg, VA 24060, USA.
authors.forename: Harold R
authors.initials: HR
authors.lastname: Garner
authors.affiliation: Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, USA pawel@vbi.vt.edu.
authors.forename: Pawel
authors.initials: P
authors.lastname: Michalak
mesh_terms: D000818:Animals; D002466:Cell Nucleolus / Q000235:genetics* / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D044127:Epigenesis, Genetic; D005260:Female; D020868:Gene Silencing; D020459:Genes, rRNA; D018392:Genomic Imprinting; D006824:Hybridization, Genetic; D008297:Male; D012335:RNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D019849:Sex Determination Processes; D014981:Xenopus / Q000235:genetics*
chemical_list: D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; C088179:RNA, ribosomal, 45S
keywords: 18S ribosomal RNA (rRNA); Xenopus; genetic conflicts; interspecies hybrids; nucleolar dominance