Author contributions
D.W.B. designed the research. D.W.B., R.W., C.P.R., D.L.C., K.M.H., M.S.K., M. Kothari, G.H.G., V.B.K., W.E.K., D.T.S.L., C.F.P., M.E.R., M.B., S.K.D., L.F., W.J.H., M. Kebbe, D.C.P., S.B.R., I.S. and B.S. conducted the research. C.P.R., D.L.C., M.S.K. and D.T.S.L. prepared the DNA methylation datasets. D.W.B., R.W. and C.P.R. analyzed the data. D.W.B. and R.W. wrote the first draft of the paper. D.W.B. and C.P.R. wrote the revised draft of the paper. All authors contributed critical review of the paper.