NTRK1 and major depressive disorder: Both during development and in adult homeostasis, cilia facilitate cellular signal transduction along major signaling pathways, including Hedgehog, Wnt, Notch, transforming growth factor B, G protein-coupled receptors, receptor tyrosine kinases, extracellular matrix receptors [85,86,87,88], pathways that are known to be perturbed in MDD [89,90].