In addition to data for the adult brain, we also added PsychENCODE Hi-C data for the fetal brain into the comparison, assessing the degree to which the chromatin differences between developmental stages relate to those between tissues (Fig. 5D). We found that whereas Hi-C datasets for the adult brain clustered together, the Hi-C dataset for the fetal brain was distinct (Fig. 5D and fig. S39). Only ~31% of the interactions in our adult Hi-C data were detected in the fetal dataset (figs. S39 and S40) (13). Though hard to exactly quantify, this difference appears to be larger than that seen from cross-tissue transcriptome comparison, with fetal samples included (fig. S41). We did a number of other comparisons between fetal and adult brain Hi-C datasets, analyzing the regulatory elements and genes linked by each. As expected, we found fetus-linked genes to be more highly expressed prenatally and adult-linked ones postnatally (Fig. 5E). In addition, the fetus-linked genes were preferentially expressed in developmental cell types (Fig. 5F). They were also highly expressed in adult neurons, whereas the adult-linked ones were preferentially expressed in glia, reflecting known cell-type composition (Fig. 5, D and F) (42).
