An important justification of genome projects in general is the notion that there should be a strong correlation between genotype and phenotype. C. elegans and C. briggsae show more differences at the genomic level than humans compared to mice . However, the behavior and anatomy of these nematodes are overall very similar. C. elegans and C. briggsae shared the last common ancestor 80-100 million years ago . Here we present a detailed analysis of the embryogenesis of C. elegans, C. briggsae, C. remanei and C. brenneri. Microscopic 4D analyses, including the terminal differentiation patterns and bioinformatical quantifications of cell behavior show that the embryogenesis of these nematodes cannot be distinguished. Thus, significantly differing genomes lead to morphological processes that are almost completely identical. To determine whether this process is also almost identical in more distantly related nematodes, we analyzed Pristionchus pacificus, which separated from C. elegans more than 280-430 million years ago . We found that up to the pre-morphogenetic stage, when embryos contain 400 cells and are about to undergo morphogenesis, the Caenorhabditis species and P. pacificus share (beside some minor differences such as, for example, an additional cell death after the 9th cleavage round) identical cell positions and fates. However, starting with the pre-morphogenetic stage, development in P. pacificus and the Caenorhabditis species analyzed takes two different paths. We propose that in nematodes, the pre-morphogenetic stage may be equivalent to the so called ‘phylotypic stage’ that Klaus Sander proposed to be a conserved embryonic stage in other animals .
1. Stein, L.D., et al., The genome sequence of Caenorhabditis briggsae: a platform for comparative genomics. PLoS Biol, 2003. 1(2): p. E45.
2. Hillier, L.W., et al., Comparison of C. elegans and C. briggsae genome sequences reveals extensive conservation of chromosome organization and synteny. PLoS Biol, 2007. 5(7): p. e167.
3. Dieterich, C., et al., The Pristionchus pacificus genome provides a unique perspective on nematode lifestyle and parasitism. Nat Genet, 2008. 40(10): p. 1193-8.
4. Sander, K., Specification of the Basic Body Pattern in Insect Embryogenesis. Advances in Insect Physiology, 1976. 12: p. 125-238.
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