Increased Tau Expression Correlates with Neuronal Maturation in the Developing Human Cerebral Cortex

Tau mRNA expression correlates with laminae and neuronal maturation according to sc-RNAseq. A, B, Tau mRNA expression by lamina and neuronal maturation markers in a publicly available scRNAseq dataset. Mature neurons defined as synaptophysin positive and negative for more immature markers, and radial glia as GFAP and nestin positive; 90 values (laminae) and 59 values (cell type) were outside the range and are not shown for clarity. Pseudo-laminae are defined by correlation with microdissected tissue expression patterns in the original publication (Nowakowski et al., 2017).

Validation of MAPT RNAscope probe. A FFPE tau P301L AAV-injected mouse brain was stained with a red chromogenic kit (RNAscope 2.5 HD Manual Assay kit) using the same RNAscope MAPT probe used for fluorescent imaging, with a wild-type mouse receiving no injection as a control.

Pattern of tau mRNA expression in the fetal brain by RNAscope. A, Representative MAPT RNA expression by RNAscope in 22 PCW cortical section of fetal brain. All images are from the same representative fetal brain in the designated region (subventricular zone, white matter, and cortical plate). Blue staining represents DAPI. Scale bar: 10 µm. B, The mean difference between samples expressed in a Cumming estimation plot. Raw data are plotted on the upper graph, while the lower graph shows the mean differences as bootstrap sampling distribution. Each mean difference is depicted as a dot, and the confidence interval is indicated by the vertical error bars. Two images of each of the three regions outlined above were taken from five separate cases for quantification. C, Representative H&E-stained image of a FFPE 22 PCW fetal brain tissue section with the areas of interest indicated. Scale bar: 500 μm. CP, cortical plate; SP, subcortical plate; WM, white matter; IZ, intermediate zone; SVZ, subventricular zone.

sc-RNAseq and RNAscope of cortical organoids shows tau mRNA expression pattern similar to fetal brain. A, Boxplot of tau mRNA expression in cortical organoids at 105 d in culture. Cell types defined as in Figure 1; 193 points are outside the range and are not shown for clarity. B, Representative MAPT RNA expression by RNAscope in D35, D50, and D134 cortical organoids showing younger organoids with higher NES⁺ staining do not express high levels of MAPT in their SVZ-like regions, while the older organoids show higher MAPT⁺ and SYN⁺ co-localization in more mature regions. Scale bar: 100 µm. C, Cumming estimation plots showing mean difference between samples as in Figure 3. Two images of five organoids for each age were used for quantification, as described in the methods section. D, days in culture.