Chemotaxis by the nematode Caenorhabditis elegans: identification of attractants and analysis of the response by use of mutants

Normal and mutant thermotaxis in the nematode Caenorhabditis elegans

When grown at a temperature from 16 degrees to 25 degrees and placed on a thermal gradient, the nematode Caenorhabditis elegans migrates to its growth temperature and then moves isothermally. Behavioral adaptation to a new temperature takes several hours. Starved animals, in contrast, disperse from the growth temperature. Several mutants selected for chemotaxis defects have thermotaxis defects as well; these behaviors depend on some common gene products. New mutants selected directly for thermotaxis defects have unusual phenotypes which suggest mechanisms for thermotaxis.

The avoidance of D-tryptophan by the nematode Caenorhabditis elegans

In chemotactic studies employing countercurrent separation the nematode aenorhabditis elegans was found to avoid D-tryptophan with a threshold in the range 10(-4) to 10(-3) M. There was no response to L-tryptophan up to 10(-2) M although it appeared to partially inhibit the response to D-tryptophan.

Chemotaxis-defective mutants of the nematode Caenorhabditis elegans

The technique of countercurrent separation has been used to isolate 17 independent chemotaxis-defective mutants of the nematode Caenorhabditis elegans. The mutants, selected to be relatively insensitive to the normally attractive salt NaCl, show varying degrees of residual sensitivity; some are actually weakly repelled by NaCl. The mutants are due to single gene defects, are autosomal and recessive, and identify at least five complementation groups.

Electron microscopical reconstruction of the anterior sensory anatomy of the nematode Caenorhabditis elegans.?2UU

The complete structure of the anterior sensory nervous system of the small nematode C. elegans has been determined by reconstruction from serial section electronmicrographs. There are 58 neurons in the tip of the head. Fifty-two of these are arranged in sensilla. These include six inner labial sensilla, six outer labial sensilla, four cephalic sensilla and two amphids. Each sensillum consists of ciliated sensory neurons ending in a channel enclosed by two non-neuronal cells, the sheath and socket cells. The amphidial channel opens to the outside as does that of the inner labial sensilla so that these probably contain chemoreceptive neurons. The endings of the other sensilla are embedded in the cuticle and may be mechanoreceptive. The cell bodies of all the neurons lie near the nerve ring and their axons project into the ring or into ventral ganglia. One of the ciliated sensory neurons in each of the six inner labial sensilla makes direct chemical synapses onto a muscle making these sensory-motor neurons. The anatomy of four isogenic animals was compared in detail and found to be largely invariant. The anatomy of juveniles is nearly identical to that of the adult, but males have four additional neuron processes.

Membrane excitability: made temperature-dependent by mutations

Three mutants of Paramecium aurelia with genetic lesions at two unlinked loci lost their ability to generate action potentials when grown at high temperatures. Action potentials found at room temperature were slightly aberrant. Kinetics of phenotypic changes after temperature shifts showed that excitation is not immediately sensitive to temperature change in these mutants. The initiation of an action potential must rely on many different gene products (presumably membrane proteins) which are open to modification by conditional as well as unconditional mutations.

Cyclic-AMP-controlled oscillations in suspended Dictyostelium cells: their relation to morphogenetic cell interactions

Periodic spikes of decreased optical density were recorded in cell suspensions of Dictyostelium discoideum. Spike formation as well as changes in the redox state of cytochrome b are facultatively and independently coupled to an oscillating system which is under developmental control and presumably underlies signal transmission in aggregating cells. Cyclic AMP triggers a double response, the slow component resembling the spikes formed during spontaneous oscillations. The fast component shows characteristics of the chemotactic response to cyclic AMP. The receptor system is suggested to sense changes of cyclic AMP concentration in time. Cyclic AMP pulses interact with the oscillating system, resulting in phase shift or suppression of spike formation, and in the induction of oscillations in an early stage of development before the onset of spontaneous oscillations. Continuous flow application of cyclic AMP does not change frequency up to flow rates which extinguish oscillations.