Extended Data Fig. 1 ∣. Isolation of PSDs from immature and mature human cortices.

a, Western blot analysis of different subcellular fractions of a GW23 sample demonstrating enrichment of PSD proteins and depletion of presynaptic SYP and cytoplasmic GAPDH in the PSD fraction. Enrichment of PSD proteins after fractionation was validated for all samples subjected to mass spectrometry analysis. b, Electron micrographs of the PSD fraction isolated from a GW23 sample (scale bar: 200 nm). Arrows denote structures resembling the PSD. The experiment was performed on one sample. c, Western blot analysis of purified PSDs from different age groups demonstrating changes in GRIN2B and DLG4 during development. The experiment was performed once. d, Correlation between PSD yield and synapse number of developing human prefrontal cortex. e, Venn diagram showing the overlap between Year18_22 samples in this study and the human PSD proteomes published in Roy et al., 2017 and Bayés et al., 2011. f, UpSet plot describing the number of identified proteins and their overlaps at each age group. g, PCA plots of the samples colored by various covariates. h, Variance explained by individual covariates (n = 1765 proteins). Boxplot center: median; hinges: the 25th and 75th percentiles; whiskers: 1.5 × inter-quartile range. i, Abundance patterns of GRIN2A, GRIN2B, DLG3, and DLG4. j, Colocalization of RPS6, CTNNB1, GDI1, or CFL1 with DLG4 in second-trimester human neocortex (n = 5, 5, 5 and 5 samples, scale bar: 10 μm or 5 μm as indicated in the figure). Data are presented as mean values ± s.e.m.