Technau Group - Molecular Developmental Genetics of Cnidaria
(August 2004 - December 2008)
Cnidaria are the best studied outgroup to the Bilateria. Our group established the new model system Nematostella vectensis, a brackish water sea anemone, to study different aspects of the evolution of developmental processes.
Nematostella and Hydra polyp
Nematostella belongs to the class Anthozoa. Molecular and morphological studies suggest that Anthozoa is the basal group among the Cnidaria. Nematostella is easy
to culture in the lab and gametogenesis can be induced. Thus, embryonic
development is easily accessible.
For comparison, we also work on the hydrozoan Hydra, a fresh water polyp, one of the best studied cnidarians.
Our research is focused on four areas:
The evolution of the third germ layer, the mesoderm. In order to trace the evolution of the mesoderm, we study the role of “mesodermal” genes in a diploblast animal, i.e. that consists of two germ layers only, ectoderm and endoderm. We recently isolated a number of “mesodermal” genes and studied their expression pattern in detail throughout early embryonic and larval development until metamorphosis into a primary polyp. We focus on transcription factors that are crucially involved in the formation and differentiation of the mesoderm in Bilateria, such as Brachyury, snail, twist, forkhead and gata factors. To understand how these genes are regulated, we investigate the role of the major signaling pathways, in particular the FGF/ras/MAPK pathway and the TGF-ß pathway. Since the formation of the mesoderm is closely linked to gastrulation in all Bilateria, we examine the cellular and molecular processes during gastrulation and metamorphosis.
One of the major derivatives of the mesoderm is muscle tissue. Nematostella, like all other anthozoans, have strong retractor muscles that differentiate on one side of the endodermal mesenteries. By PCR and by an extensive EST screen we identified a number of muscle specific genes that we use as marker genes to follow the differentiation of the musculature in polyps. We currently examine how the differentiation of muscle tissue in Nematostella is regulated.
Expression of Nembra1 during embryonic and larval development of Nematostella. (A) late Blastula, (B) sideview of early gastrula, (C) view on blastopore of gastrula, (D) planula larva, (E) primary polyp. Note that expression is restricted to the blastopore region, which gives rise to the pharynx and the first pair of mesenteries.
The molecular network of Brachyury. The T-box gene brachyury plays a crucial role in mesoderm differentiation of vertebrates. In the diploblast Hydra and Nematostella, brachyury is expressed in the blastopore and its derivative in the polyp, the hypostome, which is equivalent to the Spemann organizer. Comparative expression studies in a number of basal Bilateria showed that many aspects such as the early blastoporal expression and its derivatives, are conserved among the animal kingdom. It is, however, unclear to what extent the molecular network of brachyury is also conserved. Identified upstream and downstream components of Brachyury in chordates suggest that Brachyury mediates between patterning and morphogenesis. We are therefore interested in the identification of downstream and upstream genes of brachyury as well as interacting proteins in cnidarians.
HyBra1 expression in Hydra. (A) budding polyp, (B, C) early and late budding stage, (D,E) 3hr and 48 hr head regeneration,
(F,G) embryos shortly before and during hatching of primary polyp.
Note, that HyBra1 is expressed very early whenever a head is being made.
Comparative and functional genomics. We carried out an extensive EST screen from a cDNA library of mixed embryonic and larval stages from Nematostella. Currently, in a collaboration with the Joint Genome Institute (USA), the genome of Nematostella is being sequenced and a draft genome is expected for the end of 2004. The Nematostella genome represents the first genome from a diploblast animal and will undoubtedly provide interesting insights into the evolution of metazoan genomes, complexity and diversification of basal metazoans. By the comparison of the Nematostella genome and EST data with those of Bilateria, we envisage to infer the genetic repetoire of the Ur-Eumetazoa, the common ancestor of Cnidaria and Bilateria.
Evolution of the nervous system. Cnidaria were the first animals in evolution with a nervous system. Most species only have a diffuse nerve net, which however, undergoe constant turnover and renewal from differentiating stem cells. We are interested in the molecular network of the differentiation of the nervous system and its derivatives such as eyes.