Two invertebrates, a roundworm and an arthropod, share the spotlight in this box. Both have the characteristics common to all model organisms: small size, easy cultivation in the lab, and rapid life cycles. Each has provided crucial insights into life’s workings.
This roundworm, a soil inhabitant, is arguably the best understood of all animals. This was the first animal to have its genome sequenced (in 1998), revealing about 18,000 genes. A small sampling of the contributions derived from research on C. elegans includes the following:
An adult C. elegans consists of only about 1000 cells. Because the worm is transparent, biologists can watch each organ form, cell by cell, as the animal develops from a zygote into an adult. Eventually, researchers hope to understand every gene’s contribution to the development of this worm.
Programmed cell death, or apoptosis, is the planned “suicide” of cells as a normal part of development. Researchers already know which cells die at each stage. Learning about genes that promote apoptosis may help researchers to better understand cancer, a family of diseases in which cell division is unregulated.
The first C. elegans gene to be cloned, revealed the amino acid sequence of one part of myosin, a protein required for muscle contraction.∙
Nematodes provide a good forum for preliminary testing of new pharmaceutical drugs. For example, researchers might identify a C. elegans mutant lacking a functional insulin gene, then test new diabetes drugs for the ability to replace the function of the missing gene.
Worms with mutations in some genes have life spans that are twice as long as normal. Insights into aging in C. elegans may eventually help increase the human life span.
Origin of sex
C. elegans is a hermaphrodite, so the same individuals produce both sperm and eggs. They can also reproduce asexually. Section 9.9 describes how hermaphroditic nematodes have helped biologists understand the evolution of sexual reproduction.