The formation of the vulva, the egg-laying structure of nematode females and hermaphrodites, has been at the center of our research activities over many years. We have developed the nematode vulva as a suitable „case study“ in evolutionary developmental biology and have obtained mechanistic insight into the evolutionary alterations of developmental processes by comparing P. pacificus to C. elegans. Our comparative analysis provided deep insight into the patterns and processes shaping evolutionary changes. Together, we found three major types of changes that establish the evolution of nematode vulva formation as an important example of DEVELOPMENTAL SYSTEMS DRIFT.
First, the vulva is induced by different signaling pathways in P. pacificus and C. elegans with Wnt and EGF signaling, respectively.
Second, the regulatory linkage of individual signaling pathways can change tremendously during evolution. For example, Frizzled-type receptors function as antagonist rather than agonists during P. pacificus vulva induction.
Third, important aspects of signaling already change at the micro-evolutionary level among strains of the same species. Our work of the last 15 years represents a major example of developmental systems drift.
Kienle, S. & Sommer, R. J. (2013): Cryptic variability in vulva development by cis-regulatory evolution of a HAIRY binding site. Nature Comm., 4: 1714.
Wang, X. & Sommer, R. J. (2011): Antagonism of LIN-17/Frizzled and LIN-18/Ryk in nematode vulva induction reveals evolutionary alterations in core developmental pathways. PLoS Biology, 9: e1001110.
Tian, H., Schlager, B., Xiao, H. & Sommer, R. J. (2008): Wnt signaling by differentially expressed Wnt ligands induces vulva development in Pristionchus pacificus. Current Biology, 18, 142-146.
Sommer, R. J. (2008): Homology and the hierarchy of biological systems. BioEssays, 30, 653-658.
Yi, B. & Sommer, R. J. (2007): The pax-3 gene is involved in vulva formation in Pristionchus pacificus and is a target of the Hox gene lin-39. Devolopment, 134, 3111-3119.
Zauner, H. and Sommer, R. J. (2007): Evolution of robustness in the signaling network of Pristionchus vulva development. PNAS, 104, 10086-10091.
Schlager, B., Röseler, W., Zheng, M., Gutierrez, A. & Sommer, R. J. (2006): HAIRY-like transcription factors and the evolution of the nematode vulva equivalence group. Current Biology, 16, 1386-1394.
Zheng, M., Messerschmidt, D. Jungblut, B. & Sommer, R. J. (2005): Conservation and diversification of Wnt signaling function during the evolution of nematode vulva development. Nature Genetics, 37, 300-304.
Eizinger, A. & Sommer, R. J. (1997): The homeotic gene lin-39 and the evolution of nematode epidermal cell fates. Science, 278, 452-455.
Sommer, R. J. & Sternberg, P. W. (1996): Apoptosis and change of competence limit the size of the vulva equivalence group in Pristionchus pacificus: a genetic analysis. Current Biology, 6, 52-59.