TY  - GEN
TI  - Polycomb Group Proteins in the freshwater polyp Hydra
Y1  - 2011///
AV  - public
ID  - heidok11846
KW  - Polycomb Group Proteine 
KW  -  Pho/YY1 
KW  -  ProteininteraktionenPolycomb Group proteins 
KW  -  Pho/YY1 
KW  -  Protein interactions
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/11846/
A1  - Matt, Sonja
N2  - During the development of a multicellular organism, different cell types with specific functions have to be generated, although the cells contain the same genetic information. This is achieved by a cell type specific expression of genes. The gene expression pattern and the identity of the cell have to be maintained for several rounds of cell division. The growing field of epigenetics deals with the inheritance of traits, which are not determined in the underlying DNA sequence. The long-term maintenance of gene expression patterns, which can be described as a kind of a cellular memory, is counted among epigenetic mechanisms. Different epigenetic inheritance systems like chromatin remodeling exist. For instance, the chromatin structure can be altered by the histone modifying Polycomb Group (PcG) proteins. The PcG proteins are responsible for the inheritance of the repressed state. Many genes, which are controlling development, differentiation and the cell cycle, are regulated by PcG proteins. The proteins have been shown to act as large multiprotein complexes, so-called Polycomb Repressive Complexes (PRCs). In the scope of this thesis, PcG and associated proteins have been characterized in the freshwater polyp Hydra. The PcG genes Scm and Pho/YY1 could be identified in the Hydra genome and have been cloned. Together with the already identified proteins of the PRC1 and PRC2 complexes, Hydra possesses a complete set of PcG proteins. A comparison with homologous proteins of other species could demonstrate that the functional domains of the Hydra PcG proteins are highly conserved. Interestingly, the genes of the PRC2 complex are exclusively expressed in one of the three cell lineages of Hydra. The genes are expressed in the so-called interstitial cell lineage. Studies with sexual polyps could show that the genes are also expressed in the gonads of the animals. The cell line specific expression of the genes in Hydra seems to separate interstitial cells from the epithelial cell lineages. The DNA binding protein HyYY1 has been of special interest in this study. It is a homolog of the Drosophila protein Pho and of the human transcription factor YY1. Pho can be found in a PcG complex termed PhoRC (Pleiohomeotic Repressive Complex) in combination with dSfmbt. This complex is responsible for the recruitment of the other PcG complexes to their target genes in the fruit fly. YY1 acts as a ?molecular adapter? and links the PcG complexes to so-called Polycomb Response Elements (PREs). These cis-regulatory elements can be found close to target genes and are important for the recruitment of the PcG complexes. The Hydra protein has both a zinc finger domain, which is responsible for the DNA binding, and a so-called REPO domain, which is necessary for the interaction with the PRCs. With the help of gel retardation assays, it could be demonstrated that HyYY1 can effectively interact with the DNA in a sequence-specific manner. The consensus sequence is equivalent to the CCAT-motif found in Drosophila and mammals. In the fruit fly, this sequence can be found within PREs. A polyclonal antibody against recombinantly expressed HyYY1 has been generated during this study - making immunohistochemical analyses and immunoprecipitations (IPs) possible. An indication of the interaction of HyYY1 with other PcG proteins could be provided by a Co-IP. However, this preliminary result has to be verified. In addition, it should be kept in mind that the recruitment of PcG complexes in Hydra is not necessarily dependent on Pho/YY1 and PRE sites. At least for mammals, other recruiting mechanisms are known.  The existing antibodies against HyYY1 and otherHydra PcG proteins render chromatin-IPs to identify target genes possible. Next-generation sequencing technologies will enable large-scale ChIP-Seq experiments and the future identification of PcG target genes in Hydra. 
ER  -