Samuel Ward

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.

The nematode Caenorhabditis elegans is attracted by at least four classes of attractants: by cyclic nucleotides, cAMP and cGMP; by anions, Cl - , Br - , I - ; by cations, Na + , Li + , K + , Mg + ; and by alkaline pH values. The nematode's behavioral response to gradients of these attractants involves orientation and movement up the gradient, accumulation, and then habitutation. Comparison of the tracks of wild-type and mutant animals responding to gradients of attractants indicates that sensory receptors in the head alone mediate the orientation response and that the direction of orientation is determined by the lateral motion of the head. Therefore, the orientation response is a klinotaxis.

We performed a genome-wide analysis of gene expression in C. elegans to identify germline- and sex-regulated genes. Using mutants that cause defects in germ cell proliferation or gametogenesis, we identified sets of genes with germline-enriched expression in either hermaphrodites or males, or in both sexes. Additionally, we compared gene expression profiles between males and hermaphrodites lacking germline tissue to define genes with sex-biased expression in terminally differentiated somatic tissues. Cross-referencing hermaphrodite germline and somatic gene sets with in situ hybridization data demonstrates that the vast majority of these genes have appropriate spatial expression patterns. Additionally, we examined gene expression at multiple times during wild-type germline development to define temporal expression profiles for these genes. Sex- and germline-regulated genes have a non-random distribution in the genome, with especially strong biases for and against the X chromosome. Comparison with data from large-scale RNAi screens demonstrates that genes expressed in the oogenic germline display visible phenotypes more frequently than expected.