Genomic organization of Polycomb Response Elements and its functional implication in Drosophila and other insects

The epigenetic memory is an essential aspect of multicellular organisms to maintain several cell types and their geneexpression pattern. This complex process uses a number of protein factors and specific DNA elements within thedevelopmental cues to achieve this. The protein factors involved in the process are the Polycomb group (PcG)members, and, accordingly, the DNA sequences that interact with these proteins are called Polycomb ResponseElements (PREs). Since the PcG proteins are highly conserved among higher eukaryotes, including insects, andfunction at thousands of sites in the genomes, it is expected that PREs may also be present across the genome. However,the studies on PREs in insect species, other thanDrosophila, is currently lacking.We took a bioinformatics approach todevelop an inclusive PRE prediction tool, ‘PRE Mapper’, to address this need. By applying this tool on the Drosophilamelanogaster genome, we predicted[20,000 PREs. When compared with the available PRE prediction methods, thistool shows far better performance by correctly identifying the in vivo binding sites of PcG proteins, identified bygenome-scale ChIP experiments. Further analysis of the predicted PREs shows their cohabitation with chromatindomain boundary elements at several places in the Drosophila genome, possibly defining a composite epigeneticmodule. We analysed 10 insect genomes in this context and find several conserved features in PREs across the insectspecies with some variations in their occurrence frequency. These analyses leading to the identification of PRE in insectgenomes contribute to our understanding of epigenetic mechanisms in these organisms.

The CBX family of proteins in transcriptional repression and memory

For mammals to develop properly, master regulatory genes must be repressed appropriately in a heritable manner. This review concerns the Polycomb Repressive Complex 1 (PRC1) family and the relationshipbetween the establishment of repression and memory of the repressed state. The primary focus is on the CBXfamily of proteins in PRC1 complexes and their role in both chromatin compaction and phase separation.These two activities are linked and might contribute to both repression and memory.

Induced Pluripotent Stem (iPS) Cells in Dentistry: A Review

iPS cells are derived from somatic cells via transduction and expression of selective transcription factors. Both viral-integrating (like retroviral) and non-integrating (like, mRNA or protein-based) techniques are available for the production of iPS cells. In the field of dentistry, iPS cells have been derived from stem cells of apical papilla, dental pulp stem cells, and stem cells from exfoliated deciduous teeth, gingival and periodontal ligament fibroblasts, and buccal mucosa fibroblasts. iPS cells have the potential to differentiate into all derivatives of the 3 primary germ layers i.e. ectoderm, endoderm, and mesoderm. They are autogeneically accessible, and can produce patient-specific or disease-specific cell lines without the issue of ethical controversy. They have been successfully tested to produce mesenchymal stem cells-like cells, neural crest-like cells, ameloblasts-like cells, odontoblasts-like cells, and osteoprogenitor cells. These cells can aid in regeneration of periodontal ligament, alveolar bone, cementum, dentin-pulp complex, as well as possible Biotooth formation. However certain key issues like, epigenetic memory of iPS cells, viral-transduction, tumorgenesis and teratoma formation need to be overcome, before they can be successfully used in clinical practice. The article discusses the sources, pros and cons, and current applications of iPS cells in dentistry with an emphasis on encountered challenges and their solutions.