Sanfeliu-Cerdan, Neus et al. (2021) International Worm Meeting "Transducing touch by a titin-related protein in the worm"

Sanfeliu-Cerdan, Neus, Catala-Castro, Frederic, Krieg, Michael, Porta-de-la-Riva, Montserrat

[International Worm Meeting, 2021]

Of the five traditional senses, touch is the first one available to us when we are born. Despite being a relatively little investigated sensory modality, touch governs our daily lives, from walking and feeding to kissing and cuddling. How mechanical forces reach the mechanoelectrical transduction channels remains an open question. To address this knowledge gap, we study the mechanotransduction pathway of C. elegans' gentle touch, which relies on the six touch receptor neurons that tile the body into two receptive fields. We showed that a protein-protein interaction motif at the MEC-2 C-terminus is critical for mechanosensation, without interfering with its localization. To understand the function of MEC-2 C-terminus in touch, we conditionally coupled it to different components of the cytoskeleton. This artificial coupling was able to recover nearly wildtype functions of MEC-2, implying a role in force transfer. We then combined genetic engineering, microfluidics, and FRET-based molecular tension microscopy and found that MEC-2 is under tension when a force is applied to the body wall of the worm. To uncover an endogenous binding partner of MEC-2, we performed a neuronal RNAi screening. Surprisingly, interference of unc-89/obscn, which encodes for a protein related to the giant human titin, led to decreased touch response and colocalizes with wt but not mutant MEC-2 in TRNs. In summary, our study sheds light into how mechanical forces propagate to the mechanosensitive channels and show the first example for titin in neuronal mechanotransduction.

Porta de la Riva, Montserrat et al. (2021) International Worm Meeting "Functional photon-based neurotransmission in a nociceptive avoidance circuit"

Sanfeliu Cerdan, Neus, Porta de la Riva, Montserrat, Krieg, Michael, Catala Castro, Frederic, Gonzalez, Adriana

[International Worm Meeting, 2021]

Communication between cells is essential during development, homeostasis and nervous system function. The distribution of information is carried out by secreted chemicals, which are released and perceived by different cells. Defects in neurotransmission can lead to neurological disorders and lack of adaptation of the surrounding environment. Here, we have developed a synthetic, photon-based signaling system that we used to overcome synaptic transmission defects in C. elegans, restoring the communication between nervous cells. In particular, we have replaced a conditional defect for glutamate release in the nociceptor neuron ASH with a calcium sensitive light emitting enzyme (enhanced Nanolantern). To prove functionality, we built an optimized microscope capable of detecting how cellular calcium increase triggers light production in vivo. Subsequently, light emission is coupled to downstream interneurons (AVA, AIB) expressing an ultrasensitive light-gated ion channel (Channelrhodopsin-XXL). Finally, we developed a new microfluidic device, which we call Trap'N'Slap, with the aim to deliver mechanical stimuli directly to ASH, while recording calcium transients (by means of Genetically Encoded Calcium Indicators) directly from AVA and AIB. This, together with behavioral nose touch assays, proved that quantum release from ASH, is able to recover functional communication between neurons in an endogenous circuit.

Das, Ravi et al. (2021) International Worm Meeting "Local compression mechanosensing by DVA proprioceptors curbs body bends during locomotion"

Sanfeliu-Cerdan, Neus, Porta-de-la-Riva, Montserrat, Catala-Castro, Frederic, Krieg, Michael, Pidde, Aleksandra, Das, Ravi, Lin, Li-Chun

[International Worm Meeting, 2021]

Coordinated cell shape changes is the basis for a myriad of dynamic processes in animals, from limb movement to locomotion, but also for visceral morphodynamics such as lung expansion. These processes are supervised by specialized, proprioceptive mechanosensors, which are capable to accurately transduce mechanical information from organ deformation into biochemical signals. However, we still have little knowledge about the physiologically relevant mechanical stresses and deformations that lead to the activation of mechanosensitive neurons during proprioception or visceral mechanosensation. The stereotypical locomotion phenotype of C elegans can help us elucidate several mechanotransduction pathways coming into play for proprioception. We used a conditional knock-out strategy and found that unc-70 beta-spectrin has cell-specific roles in the DVA neuron in limiting body bending amplitudes during locomotion. By means of calcium imaging, microfluidic manipulation and genetically encoded tension sensors we found that the spectrin cytoskeleton is able to bear compressive stresses that are transduced by the trp-4 ion channel of the TRPN/NOMPC family. In conjunction with optical tweezer based force spectroscopy assays of cultured DVA neurons, we found that the potassium leak channel twk-16 is responsible for inhibiting depolarization during axonal stretch, which adjusts the proprioceptive mechanism of DVA within compression. Finally, we formulate our observations within a neuromechanical framework that shows that compartmentalized, compressive mechanosensitivity triggers local muscle contraction that is critical for animal locomotion.