"Although there is an endless diversity of form in the animal
kingdom, species of unrelated phyla, such as arthropods, nematodes and
vertebrates, share a surprisingly high number of regulatory genes.
Underneath the variation in morphological and developmental design lies
a related molecular program. It has been argued that animal diversity
relies on the differential use of similar components by first the
participation of one gene product in diverse genetic networks, and
second a functional diversification through changes in the molecular
specificity of proteins. Thus, it is the function of genes, and the
regulatory linkage of these genes in more complex genetic networks that
change during the course of evolution. Only a comparison of related,
but nonetheless distinct, organisms will enable us to obtain and
interpret changes in gene function in homologous developmental systems.
This approach will provide the opportunity eventually to take
comparative developmental biology to a mechanistic level." (Eizinger et
al., Trends in Genetics, Vol. 15. 197).
The primary research theme of the Department for Evolutionary
Biology is the evolutionary analysis of developmental processes and
mechanisms. Evolutionary developmental biology has had a strong revival
in the last 15 years, building on the mechanistic insight of
developmental processes in model organisms, such as Drosophila and C. elegans
(Pires-daSilva & Sommer, 2003; Rudel & Sommer, 2003). Many of
the pioneering studies in "evo-devo" were carried out in insects other
than Drosophila with the aim to compare early embryogenesis, in particular segmentation among insects (Sommer & Tautz, 1993).
Nematodes are an attractive system for evolutionary
developmental biology for several reasons (for review see Sommer, 1997;
2001). Developmental processes can be studied at a single cell
resolution, many species can be cultured under laboratory conditions
and postembryonic processes are amenable to genetic analysis. We have
dedicated substantial efforts of our comparative work on one particular
species, Pristionchus pacificus. P. pacificus was
described as a novel species in 1996 and fulfills many technical
requirements for detailed genetic and molecular studies. Over the
years, we have generated a genetic, molecular and genomic toolkit that
establishes P. pacificus as a major satellite system for evolutionary developmental biology (for review see Simpson, 2002).
Several aspects of the biology and in particular, developmental biology of P. pacificus
have been studied in recent years. The center of our research is the
evolutionary analysis of vulva formation because the development of the
egg-laying structure is very well understood in C. elegans. Multiple cellular and molecular differences in vulva formation have been identified between P. pacificus and C. elegans.
Although the nematode vulva is a homologous organ that is formed by
homologous precursor cells, the cellular interactions as well as the
genetic interactions required for cell fate specification of vulval
cells changed dramatically over evolutionary time scales (for review
see Eizinger et al., 1999; Sommer, 2000; 2001).
The general aim of the Department is to develop the nematode vulva as a suitable "case study"
into the evolutionary alterations of developmental processes. By
studying and comparing two distantly related species of the same
phylum, such as P. pacificus and C. elegans,
macroevolutionary alterations of developmental processes and mechanisms
can be identified. Complementing this macroevolutionary approach with
microevolutionary studies within the genus Pristionchus and between different wild-isolates of P. pacificus,
will reveal insight into those types of natural variations that causes
developmental novelty. To substantiate such ideas, we have initiated
phylogenetic and ecological studies to complement the developmental
genetic approach. This might allow us to identify selective properties
that shape developmental alterations among strains and species. Taken
together, the final goal of the Department is to achieve a
comprehensive description of macro- and microevolutionary changes of
developmental mechanisms at the molecular level in a phylogenetic and
ecological context.
Selected References:
Eizinger, A., Jungblut, B. & Sommer, R. J. (1999): Evolutionary change in the functional specificity of genes. Trends Genet., 15, 197-202.
Pires-daSilva, A. & Sommer, R. J. (2003): The evolution of signaling pathways in animal development. Nature Reviews Genetics, 4, 39-49.
Rudel, D. & Sommer, R. J. (2003): The evolution of developmental mechanisms. Dev. Biol., 264, 15-37.
Simpson, P. (2002): Evolution of development in closely related species of flies and worms. Nature Review Genetics 3, 1-11.
Sommer, R. J. (2000): Evolution of nematode development. Curr. Opin. Gen. Devel., 10, 443-448.
Sommer, R. J. (2001): As good as they get: Cells in nematode vulva development and evolution. Curr. Opin. Cell Biol. 13, 715-720.
Sommer, R. J. (1997): Evolution and development - The nematode vulva as a case study. BioEssays, 19, 225-231.
Sommer, R. J. & Tautz, D. (1993): Involvement of an orthologue of the Drosophila pair-rule gene hairy in segment formation of the short germ band embryo of Tribolium (Coleoptera). Nature 361, 448-450.
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