We further see these composition changes across brain development in publicly available datasets. For example, similar changes during fetal brain development are seen in a sample of 179 undissected fetal homogenate tissues23 particularly in the proportion of pluripotent-like cells (p=6.03×10−23, Figure 2F, Supplementary Text 5), as well as the other cell types examined (Supplementary Figure 6). Large effects of cellular composition were also observed in the developing and aging postnatal brain using DNAm data on 17 postnatal subjects/brains across 16 brain regions (including 11 neocortical) from the BrainSpan project24 (Supplementary Figure 7, Supplementary Text 5). These convergent findings in combination suggest that DNAm changes in the developing and aging brain reflects a shifting cellular composition – namely loss of progenitor-like cells at birth followed by a rise of non-neuronal cells in postnatal life – that we have previously shown to manifest in the transcriptome.
