Caenorhabditis briggsae

Caenorhabditis briggsae is a small nematode, closely related to Caenorhabditis elegans. The differences between the two species are subtle. The male tail in C. briggsae has a slightly different morphology than C. elegans. Other differences include changes in vulval precursor competence and the placement of excretory duct opening. C. briggsae is frequently used to study the differences between it and the more intimately understood C. elegans, especially at the DNA and protein sequence level. Several mutant strains of C. briggsae have also been isolated that facilitate genetic analysis of this organism. C. briggsae, like C. elegans, is a hermaphrodite. The genome sequence for C. briggsae was determined in 2003.

History
Ellsworth C. Dougherty first recognized the potential of C. briggsae, which had been found by Margaret Briggs in a pile of leaves on the campus of Stanford University in Palo Alto, California, in 1944 and used in her MS studies under the direction of Dr. Arthur C. Giese (Briggs, 1946; Gochnauer, 2004). Briggs studied the lifecycle of what she identified as Rhabditis sp. in association with bacteria and in various culture media devoid of other organisms. She showed that the population could not be sustained in the absence of bacteria or even on dead bacterial cells; living bacteria were a necessary food source. However, survival of individuals was greater on some bacteria-free media than others.

Habitat
Caenorhabditis briggsae can often be found in compost, garden beds, moist mushrooms or rotting fruit rich with microorganisms and various nutrients. The organism's main habitat is often considered to be the temperate regions of the globe, often accompanying its relatives C. elegans and C. remanei.

Overview of Genome
The whole genome sequencing project (Stein et al., 2003) revealed that the genomes of C. briggsae and C. elegans have much in common. For example, both worms have the same number of chromosomes (six chromosomes each), similar genome size, and similar numbers of protein coding and non-protein coding genes. Further analysis demonstrated that about 62% of the protein coding genes in C. briggsae have orthologs in C. elegans. Nevertheless, many interesting species-specific features including species-specific genes exist, which serve as the foundation for comparative analysis.

Comparative genomics with C.elegans
Caenorhabditis briggsae is a soil nematode estimated to have diverged from C. elegans approximately 80-100 million years ago, and yet is morphologically almost indistinguishable from it. Areas of sequence encoding proteins are mostly conserved between the two species while most intergenic and intronic sequence are divergent. Areas of similarity between the sequence of the two organisms can suggest coding exons or point to regulatory regions and to RNA genes missed in standard analysis.