Molecular and Genetic Approaches for the Analysis of C. elegans Neuronal Development - Caenorhabditis Elegans: Molecular Genetics and Development - page 408

Abstract
The complete known anatomical connections of C. elegans nervous system have
provided researchers ample opportunities to discover fundamental principles under-
lying neuronal development. Transgenic labeling with fluorescent proteins in
neuronal cells has had an unparalleled impact on our ability to visualize cellular
architecture and dynamics. In this chapter, we summarize the common methods and
guidelines for dissecting the molecular and cellular mechanisms controlling nervous
system formation. We end with a brief description of several applications that
illustrate the use of these methods.
I. Introduction
A. Overview of Nervous System Anatomy
The nervous system is the most complex organ of Caenorhabditis elegans.An
adult hermaphrodite has 302 neurons and 56 glial cells, which make up almost 40%
of the somatic cells. An adult male has 383 neurons, 294 of which are common with
hermaphrodites and 89 are specific to males. The structure of the hermaphrodite
nervous system was described in unprecedented detail using electron microscopic
serial reconstruction ( White et al., 1986 ). The structure of the male nervous system
has also recently been completed by David Hall and Scott Emmons (personal
communication). In hermaphrodites, 20 neurons reside in the pharynx, forming
the pharyngeal nervous system, and 282 neurons are spatially organized into ganglia
and nerve bundles forming the somatic nervous system ( Fig. 1 A). Based on mor-
phology and position, the 302 neurons are classified into 118 types, and neurons of
the same type usually exhibit two-, four-, or sixfold symmetry along the body axis
( White et al., 1986 ). The Wormatlas ( http://www.wormatlas.org ) provides accurate
illustrations of individual neurons and up-to-date information on the function and
molecular composition. Recent findings have now revealed functional and molec-
ular differences between neurons in the same morphological group.
The soma of the majority of sensory neurons and interneurons are located in the
ganglia in the head and tail. Each ganglion is surrounded by the basement mem-
brane. The nerve processes of sensory neurons, interneurons, and anterior motor
neurons form the major neuropil in the head, called the nerve ring, or the ''brain,''
where extensive information processing occurs ( Fig. 1 A). The ventral nerve cord
(VNC) consists of a linear array of motor neuron soma and nerve processes of
interneurons and motor neurons ( Fig. 1 A, B). The dorsal nerve cord is primarily
composed of nerve processes of the motor neurons ( Fig. 1 A). The motor neurons
provide excitatory and inhibitory input to body wall muscles. The peripheral sensory
neurons include mechanosensory neurons and a few other neurons; their somas
reside at various lateral positions along the body, and extend axons singly or as a
small bundle ( Fig. 1 A). The 56 glial cells are divided into three classes: sheath
(24 cells) and socket (26 cells) cells reside in the head ganglia and surround the