Transcriptomic analysis of human Fragile X syndrome neurons reveals neurite growth modulation by the TGFβ/BMP pathway

Isogenic hESC clones with and without the FX mutation that share the same genetic background were in vitro differentiated into neurons. FX neurons present delayed neuronal development and maturation with full FMRP silencing. Following enrichment of neurons in the culture by MACS, transcriptome analysis by RNA sequencing at different time points during differentiation demonstrated dysregulation of the TGFβ/BMP signaling pathway and genes related to the extracellular matrix. FX neurons showed decreased neurite outgrowth that was rescued by inhibition of the TGFβ/BMP signaling pathway, this treatment did not affect the outgrowth of control neurons. In FMRP expressing neurons the regulation of the TGFβ/BMP pathway allow typical neurite outgrowth and axonogenesis that will eventually result in normal neuronal network activity. In contrast, in FX neurons the lack of FMRP dysregulate members of the BMP signaling pathway associated with the ECM organization that in a yet unknown mechanism, reduces the guidance of axonal growth cones, leading to an aberrant neuronal network function. Overall, our results provide new insights into the molecular pathways by which loss of FMRP affects neuronal network development which probably leads to its aberrant function in FXS. Comparative gene expression profiling analysis of RNA-seq data for Isogenic human embryonic stem cells clones with and without the Fragile X mutation that share the same genetic background and its neuronal differentiation derivatives (neural precursor cells, glial cells and neurons).