Fig. 1: LRRTM1 controls excitatory synapse number in the mPFC and is interdependently expressed with SynCAM 1.
a Representative immunostainings of mPFC layer II/III of WT (top) and LRRTM1 KO (bottom) mice at P50 for the excitatory pre- and post-synaptic markers vGlut1 and Homer1. Single optical 1.0 μm confocal sections were acquired from anterior cingulate, prelimbic, and infralimbic areas. A machine-learning algorithm traced vGlut1 and Homer puncta (red and white, respectively, in merge). Scale bar, 5 μm. b Fewer excitatory synapses in the mPFC of mice lacking LRRTM1. Overlapping vGlut1/Homer1 sites from images as in a were scored as excitatory synapses. (Student’s t-test; n = 35 ROI WT, 64 LRRTM1 KO from 4 mice of both sexes per genotype). c Increase in α- but not β-Neurexins in synaptosomes from LRRTM1 KO PFC compared to WT. Left, immunoblots, 30 μg protein loaded per lane. Right, quantification normalized to loading control. (Unpaired t-test, two-tailed; n = 5 WT and 5 LRRTM1 KO mice for α-Neurexins; n = 5 WT and 4 LRRTM1 KO for β-Neurexins). d Left, immunoblots for Neuroligin-1 in synaptosomes from WT and LRRTM1 KO PFC. 30 μg protein loaded per lane. Right, quantification normalized to loading control. (Unpaired t-test, two-tailed; n = 6 WT and 5 LRRTM1 KO). e Increase in SynCAM 1 in synaptosomes from LRRTM1 KO PFC compared to WT. Left, immunoblots, 15 μg protein loaded per lane. Right, quantification normalized to loading control. (Unpaired t-test, two-tailed; n = 6 WT and 5 LRRTM1 KO). f mPFC sections of WT and LRRTM1 KO mice at P55 immunostained for SynCAM 1 (blue), Homer (green), and Gephyrin (red). Left, merge; right, SynCAM 1 signal. Single 1.0 μm confocal sections were acquired. g SynCAM 1 immunoreactivity in the mPFC layer II/III is increased in LRRTM1 KO mice compared to WT. Images as in f were quantified. (Unpaired t-test, two-tailed; n = 63 ROI from 4 WT, 66 from 4 LRRTM1 KO). *p < 0.05, ***p < 0.001, ns not significant. Error bars in bar graphs show Standard Error of the Mean. In box-and-whisker plots, the box extends from the 25th to 75th percentiles and the middle line is plotted at the median, with whiskers to maxima and minima. Mr given in kilodaltons. Source data for panels b, c, d, e, and g are provided as a Source Data file.
