TEXT S6: DNA METHYLATION TOOL KIT
Garret Suen1,2 and Chris R. Smith3
1Department
of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, United States of
America
2DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI 53706,
United States of America
3Department of Biology, Earlham College, Richmond, IN 47374, United States of America
DNA Methylation is a process whereby a methyl group is added to cytosine in
DNA, and it is known to be an important regulator of gene expression across many
animal species [1,2]. In insects, DNA methylation is known to be implicated in caste
development [3], sex development [4], and genomic imprinting [5]. A total of three DNA
methyltransferase genes are thought to be involved in this process, named Dnmt1,
Dnmt2, and Dnmt3, although the precise role of Dnmt2 in DNA methylation remains
unconfirmed. All three genes are found in the other two sequenced hymenopteran
genomes and there appears to be an expansion in Dnmt1 with Apis mellifera containing
2 copies of this gene and Nasonia vitripennis containing 3 copies [6]. Using the models
for these genes from Apis and Nasonia, we identified single copies of Dnmt1, Dnmt2,
and Dnmt3 in the genome of Atta cephalotes, suggesting that the duplication of Dnmt1
in both Apis and Nasonia may be lineage-specific. Given the role of these three genes
in other hymenopterans, it is likely that they play the same role in Atta. Dnmt1 is known
as a maintenance methyltransferase that is thought to preserve DNA methylation states
across germ lines and thus has been directly implicated in genomic imprinting. Dnmt2 in
contrast, is known to methylate RNA [7] although a direct function for this has not been
determined. One possible function may be that it is involved in silencing transposable
elements, which has been shown for homologs in bacteria [8]. Dmnt3 is also a
methyltransferase that responds to external stimuli, and its knockdown in Apis is known
cause larvae to develop into queens, implicating its role in caste development in social
insects [3]. Given these roles, it is likely that these genes follow similar functions in A.
cephalotes. Specifically, Dmnt3 may have a prominent role given its role in honey bee
queen development, and given the wide range of morphological castes in A. cephalotes,
these genes may participate in both the regulation of worker caste and queen
development.
References
1. Razin A, Riggs AD (1980) DNA methylation and gene function. Science 210: 604.
2. Bird AP (1986) CpG-rich islands and the function of DNA methylation. Nature 321:
209.
3. Kucharski R, Maleszka J, Foret S, Maleszka R (2008) Nutritional Control of
Reproductive Status in Honeybees via DNA Methylation. Science 319: 1827.
4. Beukeboom LW, Kamping A, van de Zande L (2007) Sex determination in the
haplodiploid wasp Nasonia vitripennis (Hymenoptera: Chalcidoidea): A critical
consideration of models and evidence. Seminars in Cell & Developmental
Biology 18: 371.
5. Field LM, Lyko F, Mandrioli M, Prantera G (2004) DNA methylation in insects. Insect
Molecular Biology 13: 109.
6. Werren JH, Richards S, Desjardins CA, Niehuis O, Gadau J, et al. (2010) Functional
and Evolutionary Insights from the Genomes of Three Parasitoid Nasonia
Species. Science 327: 343-348.
7. Goll MG, Kirpekar F, Maggert KA, Yoder JA, Hsieh C-L, et al. (2006) Methylation of
tRNAAsp by the DNA Methyltransferase Homolog Dnmt2. Science 311: 395.
8. Bestor TH (1990) DNA Methylation: Evolution of a Bacterial Immune Function into a
Regulator of Gene Expression and Genome Structure in Higher Eukaryotes.
Philosophical Transactions of the Royal Society of London Series B, Biological
Sciences 326: 179.