Setty, Hagar et al. (2021) International Worm Meeting "Sexually dimorphic neuronal circuitry drives distinct mechanosensory responses"

Setty, Hagar, Oren, Meital

[International Worm Meeting, 2021]

The recent publication of the anatomical maps of the nervous system of both sexes in C. elegans revealed an abundance of dimorphic connectivity between sex-shared neurons. However, the molecular mechanisms that underlie the development of sexually dimorphic neuronal circuits are poorly understood. We focus on the sex-shared interneuron AVG, which in hermaphrodites receives very little inputs, but in males receives many inputs from both male-specific and sex-shared sensory neurons. By combining behavioral assays with optogenetic manipulation and tracking of freely moving animals, we discovered a novel dimorphic role for AVG in tail mechanosensation and locomotion. Specific silencing of AVG using histamine-gated chloride channels revealed it is required only in males for tail-touch response (a forward movement of the worm in response to a touch applied to the tail (Li et al, 2011)). Optogenetic inhibition of AVG inhibited the locomotive behavior of males, but not hermaphrodites. Calcium imaging experiments using a microfluidic device for mechanical stimulation (Fehlauer et al, 2018) further support a role for AVG in tail mechanosensation. To discover molecular candidates that mediate tail mechanosensation we carried out a reverse genetic screen. We found that the AMPA glutamate receptor glr-1 is required for tail mechanosensation only in hermaphrodites, while the NMDA glutamate receptor nmr-1 is required in both sexes, with a stronger effect in males. To test whether nmr-1 and glr-1 function cell autonomously in AVG, we analyzed the tail-touch responses of mutant animals with a masculinized AVG. Masculinizing AVG in nmr-1 mutants reduced the response of hermaphrodites to that of the males, while masculinizing AVG in glr-1 mutants did not alter the phenotype of the tail-touch response. Our preliminary results suggest that nmr-1, but not glr-1, mediate tail mechanosensation in males through AVG. To investigate the sensory input to AVG, we focused on the sex-shared sensory neurons PHA, PHB and PHC, which generate sexually dimorphic connections with AVG (Cook et al, 2019). Silencing PHA and PHB revealed that PHA is required for tail mechanosensation only in males, while PHB is required in both sexes. PHC silencing affected only hermaphrodites, corroborating previous results by Serrano-Saiz et al, 2017. To summarize, our results show that the circuit for tail mechanosensation is sexually dimorphic in all aspects - molecular, cellular and behavioral.

Atwell, K. et al. (2015) International Worm Meeting "A computational model of cell mechanics and decision-making in the C. elegans germ line."

Atwell, K., Osborne, J.M., Qin, Z., Kugler, H., Gavaghan, D.J., Hubbard, E.J.A.

[International Worm Meeting, 2015]

Understanding germline development as a whole can be challenging. The combination of cell-cell signalling, systemic effects, gonad growth, cell mechanics and movement all complicate the link between individual cell behaviour and whole organ properties. Computer models provide one approach to address this challenge. They can also provide testable predictions and can aid in interpreting data.We have produced a dynamic, 3D model of the C. elegans germ line that builds on previous work (Setty et al. 2012) by incorporating both the mechanical forces between cells and a model of the decision-making molecular processes at work inside cells. The mechanics component of the model was built using the software Chaste (Cancer Heart and Soft Tissue Environment; Mirams et al. 2013) and represents cells as deformable spheres that exert force on each other when they overlap. The behaviour of individual germ cells is determined by a Statechart (Harel 1987), a formalism for representing complex systems that is widely used in engineering and computer science. By applying a growing gonad boundary condition that forms along the path of the DTC we were able to simulate both larval development and adult homeostasis in a single program run.Our simulations produce a reasonable agreement with experiment across a range of measured germ line properties, including ovulation rate, sperm count and total cell count. To achieve this fit, we found that two new biological properties had to be incorporated into the model. First, we include a period of "stretching" growth during late L4, in which the turn region of the gonad moves centrifugally. We measured this growth in larval stage worms and speculate that it may result from germ cell pressure inside the gonad. Second, we included contact inhibition among proliferative germ cells. This robustly stabilized proliferative cell numbers at a reasonable level compared to attempts to balance a fixed cell proliferation rate and a fixed death rate. Finally, we also demonstrate in silico cell tracking and lineage labelling between L3 and adulthood.