Sengupta, Titas et al. (2021) International Worm Meeting "A retrograde zippering mechanism regulates neurite placement in the C. elegans nerve ring"

Koonce, Noelle, Santella, Anthony, Bao, Zhirong, Wu, Yicong, Moyle, Mark, Han, Xiaofei, Fan, Li, Shroff, Hari, Mohler, William, Colon-Ramos, Daniel, Shao, Lin, Vazquez-Martinez, Nabor, Duncan, Leighton, Sengupta, Titas

[International Worm Meeting, 2021]

A fundamental design principle of nervous systems is the grouping of neuronal contacts into layers within nerve bundles. The layered arrangement of neurites requires nanoscale precision in their placement within bundles, and this precision, which cannot be exclusively explained by simple tip-directed outgrowth dynamics, underpins synaptic specificity and circuit architecture. Here we implement novel imaging methods to document the specific placement of single neurites during the assembly of the C. elegans nerve ring. We uncover a retrograde zippering mechanism that controls precise placement of neurites along specific layers. Nanoscale precision in neurite placement is orchestrated via temporally-regulated expression of Ig adhesion molecule SYG-1. SYG-1 acts as an instructive signal, defining layer boundaries and guiding neurite zippering onto target neurons. SYG-1 acts through its canonical ligand SYG-2 and SYG-1 extracellular domains are sufficient for instructing neurite placement. Our study suggests that adhesion-mediated retrograde zippering might be an important developmental mechanism that coordinates neurite placement and synaptic connectivity within brain neuropil bundles in vivo.

PD Wes et al. (1999) International C. elegans Meeting "Information Coding in the C. elegans Olfactory System"

PD Wes, CI Bargmann

[International C. elegans Meeting, 1999]

Different signal transduction pathways coexist within the same cell, interacting in complex ways to produce novel responses, yet preserving fidelity. The olfactory system of C. elegans can be used to study the molecular basis of information processing within a single cell. C. elegans senses a broad array of attractive odors with just two pairs of sensory neurons, AWA and AWC. A number of odorants activate each neuron. Isoamyl alcohol (iaa), 2,3-pentanedione (pd), butanone (bt) and benzaldehyde (bz) all activate AWC, and, furthermore, each odorant utilizes the same cGMP signaling cascade. Nevertheless, animals are able to distinguish amongst some of these odorants. For instance, when placed in a uniform field of bt, animals will no longer chemotax toward a point source of bt (defined as saturation), yet will chemotax toward bz. A screen was conducted to identify mutants that responded normally to bz in the absence of bt, but failed to chemotax toward a point source of bz in a field of bt (defined as cross-saturation). 20,000 haploid genomes were screened, yielding 25 candidates. A range of phenotypes was observed, with the strongest mutant, ky542 , displaying total cross-saturation of bz by bt. ky542 exhibits other defects in odor recognition or processing. It has reduced sensitivity to pd, though its sensitivity to all others odorants remains undiminished. ky542 also has enhanced discrimination between iaa and bz. Olfactory discrimination is also enhanced by starvation, a form of plasticity modulated by serotonin 1 . In addition, ky542 and other cross-saturation mutants display a defect in olfactory adaptation, a long-lasting form of signal desensitization (see abstract by Noelle l'Etoile and C.B.). Several models that may shed light on these olfactory phenotypes are being tested. Understanding the principles behind olfactory discrimination may provide new insights into information coding within single cells, and may also elucidate some forms of behavioral plasticity that are modulated by C. elegans olfaction. 1 Colbert, H.A., Bargmann, C.I. 1997.