Abstract

I have characterized a Caenorhabditis elegans Ca²⁺ binding protein, C. elegans Neuronal Calcium Sensor-1 (Ce-NCS-1), member of the recoverin/neuronal calcium sensor-family (NCS-family). Ce-NCS-1 is an EF-Hand calcium binding protein highly related to other Neuronal Calcium Sensor -1 sequences found from mammals to yeast. Together, these likely ortholog sequences form the NCS-1 sub-family of NCS proteins. These proteins are thought to be involved in the fine-tuning of neuronal calcium dependant processes.

In C. elegans NCS-1 is expressed predominantly in certain head sensory neurons required for dauer formation, chemotaxis and thermotaxis. Ce-NCS-1 is expressed in AFD and AIY neurons known to be indispensable for upward migration in a temperature gradient and for proper isothermal tracking.

The homozygous ncs-1 knock-out mutant is viable, fertile and looks healthy but shows thermotaxis defects.

Thermosensation allows C. elegans to stay in a favorable temperature environment associated with the presence of food. In a temperature gradient, wild type C. elegans migrate and accumulate to their growth temperature and then move isothermally. Wild type worms placed in a radial temperature gradient make circular isothermal tracks at the level of their cultivation temperature. The thermal behavior is plastic; adaptation to a new growth temperature takes several hours.

The ncs-1 knock-out is unable to make stable isothermal tracks at its eccritic temperature in a radial temperature gradient showing an athermotactic phenotype. The mutant does not "remember" its growth temperature or does not sense temperature or could not coordinate thermosensory information with motor output.

I propose that Ce-NCS-1 may modulate sensory - motor coordination together with thermal information retrieval required in the fine control of isothermal radial movements.