Vitar, M. | bioRxiv Science

bioRxiv2026

A filopodia-based dendritic mechanosensory compartment in CSF-contacting neurons

Cerebrospinal fluid-contacting neurons (CSF-cNs) are spinal sensory cells that detect chemical and mechanical stimuli via PKD2L1 channels located on a primary cilium, as established in aquatic vertebrates like zebrafish. The mechanosensory mechanism in mammals, however, has remained unclear due to the absence of definitive evidence for cilia on their apical processes (ApPrs). Here we show that mouse CSF-cN ApPrs lack cilia but instead possess drebrin-stabilized filopodia enriched with F-actin. Mechanical stimulation of these cilia-free ApPrs elicits robust, PKD2L1-dependent inward currents, that are sufficient to drive neuronal firing, confirming a novel, cilia-independent mechanosensory mechanism. Comparative analyses indicate an evolutionary divergence from ciliary mechanotransduction, with mice adopting a direct, actin-associated mechanism. These findings advance our understanding of the cellular basis of spinal mechanosensation in mammals and reveal a specialized adaptation for monitoring central canal dynamics, with implications for spinal sensory integration and evolution. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/713694v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@f74408org.highwire.dtl.DTLVardef@193866forg.highwire.dtl.DTLVardef@5f1baaorg.highwire.dtl.DTLVardef@113c3e_HPS_FORMAT_FIGEXP M_FIG C_FIG In BriefCerebrospinal fluid-contacting neurons detect mechanical forces in the spinal cord. In zebrafish, they use a cane-like cilium. Whether mammals inherited this mechanism is controversial. Here, researchers show that mice have replaced the cilium with filopodia, hair-like, touch-sensitive projections stabilized by the protein drebrin. This evolutionary innovation reveals how sensory cells adapt their machinery to the demands of different body plans and environments. HIGHLIGHTS- Mouse spinal CSF-cN apical processes lack cilia. - Drebrin-stabilized filopodia replace the ancestral cilium. - Direct mechanical stimulation of ApPrs evokes PKD2L1-dependent currents and firing. - Mammalian CSF-cNs evolved a cilia-independent mechanosensory mechanism.

neuroscience↗

bioRxiv2025

PH sensitivity of cerebrospinal fluid-contacting neurons involves the modulation of phasic and tonic currents mediated by PKD2L1 channels located in the apical process.

Cerebrospinal fluid contacting neurons (CSFcNs) are GABAergic cells that surround the central canal (cc) of the spinal cord. Their soma is located sub-ependymally and they have a dendritic-like process that ends as a bulb (the so-called "apical process"; ApPr) inside the cc. It remains unclear how this unique anatomical organization, with the soma and the ApPr located in different extracellular environments, relates to their function as a multimodal sensor of cerebrospinal fluid (CSF) composition. One of the main physiological features of CSFcNs is a prominent spontaneous electrical activity mediated by PKD2L1 channels, a non-selective cation channel of the TRP family. PKD2L1 channels have a high single-channel conductance (around 200 pS) and can be modulated by protons and mechanical forces. In this work we investigate PKD2L1 channel sensitivity to pH and its effects on CSFcNs excitability. We demonstrate that PKD2L1 spontaneous activity generates not only phasic inward currents, but also a sustained current, both of which are modulated bidirectionally by pH with a high sensitivity around physiological values. By combining electrophysiology (direct recordings from intact and isolated ApPrs) with optical methods (laser-photolysis of protons) we further show that functional PKD2L1 channels are specifically localized in the ApPr. The spatial segregation of PKD2L1 channels, along with their biophysical properties (high single-channel conductance and pH sensitivity) and the ApPrs unique membrane properties (very high input resistance) renders CSFcN excitability exquisitely sensitive to PKD2L1 modulation. Altogether, our findings illustrate how the ApPrs properties are finely tuned to support its sensory role.

neuroscience↗