Fig. 4: Prmt9 cKO hippocampus neurons show impaired excitatory synapse development.

a Photomicrograph of CA1 hippocampus neurons and their representative dendritic arborization. Scale bar, 200 μm. b Representative apical dendritic segments with reconstructed dendritic spines. Scale bar, 10 μm. c Prmt9 cKO CA1 neurons (n = 11) showed reduced dendritic spine density compared to that from WT (n = 10) neurons (p = 0.0027, unpaired t test). Data are presented as mean ± SEM. d Prmt9 cKO mice showed reduced dendritic spine head volume/size in CA1 neurons (cKO, n = 141 spines/7 neurons; WT, n = 133 spines/8 neurons. p = 0.019, Kolmogorov-Smirnov test). Box plot indicates min, lower quartile Q1, median, upper quartile Q3 and max. e Representative co-labeling of synapse markers, including the glutamate receptor subunits (GluA1/GluN1) and the pre- and post-synaptic proteins (Synapsin I/PSD95) in WT control and Prmt9 cKO mice (n = 3). Scale bar, 20 μm. f Quantification of GluA1/GluN1 and Synapsin I/PSD95 puncta density and double labeling. Cultured Prmt9 cKO hippocampal neurons show reduced puncta density for GluN1 (p = 0.0003) and GluA1 (p = 0.002) compared to WT/control neurons (two-way ANOVA with Sidak’s MCT). In addition, cKO hippocampal neurons show reduced density for PSD95 puncta (p = 0.002). Reduced proportion of functional excitatory synapses, defined by the proportion of colocalized GluA1/GluN1 (p < 0.0001, n = 13 neurons for control and cKO) and Synapsin I/PSD95 (p < 0.0001, n = 14 neurons for control and cKO) was observed in cKO neurons as well. Box plot indicates min, lower quartile Q1, median, upper quartile Q3 and max. g Exemplary whole cell mEPSC traces from WT and Prmt9 cKO CA1 neurons. h Cumulative and percentage distribution of mEPSC amplitudes from WT control and Prmt9 cKO CA1 neurons. Prmt9 cKO neurons showed decreased mEPSC amplitude (p = 0.015, Kolmogorov–Smirnov test). i Prmt9 cKO CA1 neurons show reduced mEPSC frequency (WT, n = 16 neurons; cKO, 15 neurons. p = 0.004). j Prmt9 cKO CA1 neurons exhibit significantly smaller AMPA/NMDA current ratio (WT, n = 10 neurons; cKO, n = 11 neurons. p = 0.02). Data are presented as mean ± SEM. k Input–output responses in CA1 field potential recordings, measured by fEPSP slope as a function of fiber volley amplitude (WT, n = 9 slices; cKO, n = 8 slices. p = 0.003). l Paired pulse responses across 20–100 ms ISI as a measure of presynaptic function (WT, n = 10 slices; cKO, n = 10 slices. p = 0.46 for the effects of genotype). m Prmt9 cKO hippocampus CA1 show a significantly lowered LTP magnitude, measured as the last 10-min responses (WT, n = 10 slices; cKO, n = 10 slices. p < 0.0001 for the effects of genotype).