The limited specimen tilting range that is typically available in electron tomography gives rise to a region in the Fourier space of the reconstructed object where experimental data are unavailable - the missing wedge. Since this region is sharply delimited from the area of available data, the reconstructed signal is typically hampered by convolution with its impulse response, which gives rise to the well-known missing wedge artefacts in 3D reconstructions. Despite the recent progress in the field of reconstruction and regularization techniques, the missing wedge artefacts remain untreated in most current reconstruction workflows in structural biology. Therefore we have designed a simple Fourier angular filter that effectively suppresses the ray artefacts in the single-axis tilting projection acquisition scheme, making single-axis tomographic reconstructions easier to interpret in particular at low signal-to-noise ratio in acquired projections. The proposed filter can be easily incorporated into current electron tomographic reconstruction schemes.

• Keywords
• Electron tomography, Missing wedge, Missing wedge artefacts, Single-axis tilting,
• MeSH
• Artifacts MeSH
• Fourier Analysis MeSH
• Rats MeSH
• Corylus ultrastructure   MeSH
• Cerebellum ultrastructure   MeSH
• Image Processing, Computer-Assisted * MeSH
• Signal-To-Noise Ratio MeSH
• Pollen ultrastructure   MeSH
• Electron Microscope Tomography methods   MeSH
• Trypanosoma brucei brucei ultrastructure   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, N.I.H., Extramural MeSH

The study of embryonic stem cells is in the spotlight in many laboratories that study the structure and function of chromatin and epigenetic processes. The key properties of embryonic stem cells are their capacity for self-renewal and their pluripotency. Pluripotent stem cells are able to differentiate into the cells of all three germ layers, and because of this property they represent a promising therapeutic tool in the treatment of diseases such as Parkinson's disease and diabetes, or in the healing of lesions after heart attack. As the basic nuclear unit, chromatin is responsible for the regulation of the functional status of cells, including pluripotency and differentiation. Therefore, in this review we discuss the functional changes in chromatin during differentiation and the correlation between epigenetics events and the differentiation potential of embryonic stem cells. In particular we focus on post-translational histone modification, DNA methylation and the heterochromatin protein HP1 and its unique function in mouse and human embryonic stem cells.

• Keywords
• Chromatin, Differentiation, Embryonic stem cells, Epigenetics, Nucleus, Pluripotency,
• Publication type
• Journal Article MeSH