title: Parent-of-origin effects on genome-wide DNA methylation in the Cape honey bee (Apis mellifera capensis) may be confounded by allele-specific methylation.
abstract: BACKGROUND
  Intersexual genomic conflict sometimes leads to unequal expression of paternal and maternal alleles in offspring, resulting in parent-of-origin effects. In honey bees reciprocal crosses can show strong parent-of-origin effects, supporting theoretical predictions that genomic imprinting occurs in this species. Mechanisms behind imprinting in honey bees are unclear but differential DNA methylation in eggs and sperm suggests that DNA methylation could be involved. Nonetheless, because DNA methylation is multifunctional, it is difficult to separate imprinting from other roles of methylation. Here we use a novel approach to investigate parent-of-origin DNA methylation in honey bees. In the subspecies Apis mellifera capensis, reproduction of females occurs either sexually by fertilization of eggs with sperm, or via thelytokous parthenogenesis, producing female embryos derived from two maternal genomes.
  
  
  RESULTS
  We compared genome-wide methylation patterns of sexually-produced, diploid embryos laid by a queen, with parthenogenetically-produced diploid embryos laid by her daughters. Thelytokous embryos inheriting two maternal genomes had fewer hypermethylated genes compared to fertilized embryos, supporting the prediction that fertilized embryos have increased methylation due to inheritance of a paternal genome. However, bisulfite PCR and sequencing of a differentially methylated gene, Stan (GB18207) showed strong allele-specific methylation that was maintained in both fertilized and thelytokous embryos. For this gene, methylation was associated with haplotype, not parent of origin.
  
  
  CONCLUSIONS
  The results of our study are consistent with predictions from the kin theory of genomic imprinting. However, our demonstration of allele-specific methylation based on sequence shows that genome-wide differential methylation studies can potentially confound imprinting and allele-specific methylation. It further suggests that methylation patterns are heritable or that specific sequence motifs are targets for methylation in some genes.
authors.affiliation: Behavior and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences A12, University of Sydney, Room 248, Macleay Building (A12), Sydney, NSW, 2006, Australia. emily.remnant@sydney.edu.au.
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Remnant
authors.affiliation: School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, 2006, Australia.
authors.forename: Alyson
authors.initials: A
authors.lastname: Ashe
authors.affiliation: Victor Chang Cardiac Research Institute, Lowy Packer Building, 405 Liverpool Street, Darlinghurst, NSW, 2010, Australia.|University of New South Wales, Kensington, NSW, 2033, Australia.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Young
authors.affiliation: Behavior and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences A12, University of Sydney, Room 248, Macleay Building (A12), Sydney, NSW, 2006, Australia.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Buchmann
authors.affiliation: Behavior and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences A12, University of Sydney, Room 248, Macleay Building (A12), Sydney, NSW, 2006, Australia.
authors.forename: Madeleine
authors.initials: M
authors.lastname: Beekman
authors.affiliation: Honey Bee Research Section, ARC-Plant Protection Research Institute, Private Bag X5017, Stellenbosch, South Africa.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Allsopp
authors.affiliation: Victor Chang Cardiac Research Institute, Lowy Packer Building, 405 Liverpool Street, Darlinghurst, NSW, 2010, Australia.|University of New South Wales, Kensington, NSW, 2033, Australia.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Suter
authors.affiliation: Biology Department, Clark University, 950 Main Street, Worcester, MA, 01610, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Drewell
authors.affiliation: Behavior and Genetics of Social Insects Laboratory, School of Life and Environmental Sciences A12, University of Sydney, Room 248, Macleay Building (A12), Sydney, NSW, 2006, Australia.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Oldroyd
mesh_terms: D000483:Alleles; D000818:Animals; D001516:Bees / Q000235:genetics*; D018899:CpG Islands; D019175:DNA Methylation; D005260:Female; D049750:Genome, Insect; D018392:Genomic Imprinting; D006239:Haplotypes; D008297:Male; D010312:Parthenogenesis
keywords: Allele-specific methylation; Apis mellifera capensis; Imprinting; Parent-of-origin effects; Thelytokous parthenogenesis