CpG methylation of a silent controlling element in the murine Avy allele is incomplete and unresponsive to methyl donor supplementation.
BACKGROUND
The viable yellow allele of agouti (A(vy)) is remarkable for its unstable and partially heritable epigenetic state, which produces wide variation in phenotypes of isogenic mice. In the A(vy) allele an inserted intracisternal A particle (IAP) acts as a controlling element which deregulates expression of agouti by transcription from the LTR of the IAP; the phenotypic state has been linked to CpG methylation of the LTR. Phenotypic variation between A(vy) mice indicates that the epigenetic state of the IAP is unstable in the germline.


RESULTS
We have made a detailed examination of somatic methylation of the IAP using bisulphite allelic sequencing, and find that the promoter is incompletely methylated even when it is transcriptionally silent. In utero exposure to supplementary methyl donors, which alters the spectrum of A(vy) phenotypes, does not increase the density of CpG methylation in the silent LTR.


CONCLUSIONS
Our findings suggest that, contrary to previous supposition, methyl donor supplementation acts through an indirect mechanism to silence A(vy). The incomplete cytosine methylation we observe at the somatically silent A(vy) allele may reflect its unstable germline state, and the influence of epigenetic modifications underlying CpG methylation.
Cropley
Jennifer E
JE
Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia.
Suter
Catherine M
CM
Beckman
Kenneth B
KB
Martin
David I K
DI
D054366:Agouti Signaling Protein / Q000235:genetics; D000483:Alleles; D000818:Animals; D001483:Base Sequence; D001622:Betaine / Q000008:administration & dosage; D002794:Choline / Q000008:administration & dosage; D018899:CpG Islands / Q000235:genetics*; D019175:DNA Methylation; D019587:Dietary Supplements; D044127:Epigenesis, Genetic / Q000187:drug effects; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage; D007426:Genes, Intracisternal A-Particle / Q000235:genetics*; D005854:Germ Cells / Q000378:metabolism; D008297:Male; D008715:Methionine / Q000008:administration & dosage; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010641:Phenotype; D011401:Promoter Regions, Genetic / Q000235:genetics; D018626:Retroelements / Q000235:genetics
D054366:Agouti Signaling Protein; D018626:Retroelements; C515183:a protein, mouse; D001622:Betaine; D005492:Folic Acid; D008715:Methionine; D002794:Choline