This primer introduces the organism and the many features that make it an outstanding experimental system, including its small size, rapid life cycle, transparency, and well-annotated genome. We survey medical cell biology goodman pdf basic anatomical features, common technical approaches, and important discoveries in C. Later, he settled on the related nematode C.
25 millimeters long and adults are 1 millimeter long. Their small size means that the animals are usually observed with either dissecting microscopes, which generally allow up to 100X magnification, or compound microscopes, which allow up to 1000X magnification. Petri dishes sitting on the base of a dissecting stereomicroscope. Bacterial lawns are visible on the surface of the agar inside the dishes but the C. The two adults are moving in this view. Tracks in the plate indicate where animals have traveled on the bacterial lawn.
An adult hermaphrodite is viewed in a compound microscope. In all pictures, anterior is to the left and ventral is on the bottom. These features have helped to make C. Researchers have also reconstructed the shape of all C.
Moreover, because of the invariant wild-type cell lineage and neuroanatomy of C. Animals increase in size throughout the four larval stages, but individual sexes are not easily distinguished until the L4 stage. The experimental strengths and the similarities between the cellular and molecular processes present in C. Once the animals deplete the bacteria, they utilize their fat supply. Without food, the development of young larval stage animals is arrested. Whenever healthy, growing animals are needed, a piece of the agar from the old plate can be transferred to a new plate with bacteria. Several other features greatly facilitate the maintenance of C.
Second, animal populations can be frozen for years and revived when needed. Third, the animal’s small size means that many can be grown in a small space. The gonad of hermaphrodites forms an ovotestis that first produces haploid amoeboid sperm that are stored in the spermatheca in the L4 stage and then near adulthood the germ line switches fate to produce much larger oocytes. Essentially hermaphrodites are females whose gonads temporarily produce sperm before they produce oocytes. Y chromosome—and the genotype of males is referred to as XO. Two of the four quadrants of body wall muscles are shown. The nervous system and muscles are omitted in this view, more clearly revealing the pharynx and intestine.
Cross-section through the anterior region of the C. Images modified from those found at www. Self-fertilizing hermaphrodites provide several advantages for genetic analysis. Thus, strains that are mutagenized are essentially isogenic.
Genetic nomenclature differs from species to species. Here, we describe the major terms used in C. Cosmids, proteins, phenotypes, and strain names are not written in italics. Mutant alleles are represented by 1-3 lowercase letters, which indicate specific laboratories, followed by a number. All gene and allele symbols are italicized, e. A heterozygous condition is indicated with a slash, e.
Chromosomal abnormalities are indicated by one or two letters after the lab code, e. One or two letters may be added after the allele name to indicate particular properties conveyed by the mutation e. When a gene has more than one mutation, such as could result from the intragenic reversion of a mutant allele, both the old and new mutations are indicated, e. To distinguish alleles of the same gene, the allele names are placed in parenthesis with no space between the gene and allele name, e.
The promoter and the protein-coding names are separated by two colons as are parts of fusion proteins. A transposon insertion into a gene is similarly shown using the transposon name and two colons, e. Mutant phenotypes are designated by the non-italicized gene name without the dash and number and with the first letter capitalized, e. Unc or Sma animals are Uncoordinated or Small in body size.
Sometimes specific amino acid changes are indicated. Two capital letters and a number, e. CB429 and TU38, designate a strain containing one or more genetic differences. None of these symbols are italicized. For strains that contain reporter genes, there are two typical designations. Males are important because they allow the exchange of genetic material needed to generate animals with different genetic compositions and to map genes. A virtually impermeable eggshell is made after fertilization, allowing the embryo to develop completely independent of the mother.
However, embryos are usually retained within the hermaphrodite until about the 24-cell stage at which time they are laid. Lethargus ends with the molting of the old cuticle. After the reproductive period, hermaphrodites can live several more weeks before dying of senescence. This property makes obtaining these progeny easy. A second genetic advantage of C.