Suv4-20h2 mediates chromatin compaction and is important for cohesin recruitment to heterochromatin.

Cohesin plays an important role in chromatid cohesion and has additional functions in higher-order chromatin organization and in transcriptional regulation. The binding of cohesin to euchromatic regions is largely mediated by CTCF or the mediator complex. However, it is currently unknown how cohesin is recruited to pericentric heterochromatin in mammalian cells. Here we define the histone methyltransferase Suv4-20h2 as a major structural constituent of heterochromatin that mediates chromatin compaction and cohesin recruitment. Suv4-20h2 stably associates with pericentric heterochromatin through synergistic interactions with multiple heterochromatin protein 1 (HP1) molecules, resulting in compaction of heterochromatic regions. Suv4-20h mutant cells display an overall reduced chromatin compaction and an altered chromocenter organization in interphase referred to as "chromocenter scattering." We found that Suv4-20h-deficient cells display chromosome segregation defects during mitosis that coincide with reduced sister chromatid cohesion. Notably, cohesin subunits interact with Suv4-20h2 both in vitro and in vivo. This interaction is necessary for cohesin binding to heterochromatin, as Suv4-20h mutant cells display substantially reduced cohesin levels at pericentric heterochromatin. This defect is most prominent in G0-phase cells, where cohesin is virtually lost from heterochromatin, suggesting that Suv4-20h2 is involved in the initial loading or maintenance of cohesion subunits. In summary, our data provide the first compelling evidence that Suv4-20h2 plays essential roles in regulating nuclear architecture and ensuring proper chromosome segregation.

Development of a new software and test setup for analyzing hVOR in very young children by vHIT.

INTRODUCTION: Earlier work revealed that vHIT examination is often difficult to perform on very young children. In particular, the calibration of the system can be difficult, as active cooperation of the patient is required. Additionally, the patient must be able to follow the examiner's instructions, which is challenging for very young children. Therefore, the aim of the present study was to develop and validate a new, software-based approach enabling vHIT testing of young children and infants. METHODS AND MATERIALS: Six patients (3 boys and 3 girls) aged 5-36 months were included in a prospective, monocentric study between January 2015 and August 2015.The newly developed intuitive software enabled calibration of the eye position signal with the subjects fixating on animated animal graphics which were projected on a screen. Testing ten healthy adults validated this new calibration and measurement method. After calibration, a vHIT goggle (EyeSeeCam ©) was used to perform head impulses in the horizontal plane while the patient was watching a movie sitting on their parent's lap or in a baby chair. At least 15 impulses to each side were obtained and the occurrence of refixation saccades was analyzed. All tests were performed by one of two experienced examiners. RESULTS: The new calibration method and modified test setup provided reproducible results for all patients tested. An increased incidence of artifacts was not observed. In 2 patients, more than one test was needed. None of the included children showed catch-up overt or catch-up covert saccades. There was no gain reduction of more than two standard deviations as compared to the normative results published in the literature on vHIT examinations of children. CONCLUSION: The proposed protocol allows vHIT testing in very young children and infants (aged 5 months to 3 years). The study emphasizes that vHIT is an easy and sensitive screening tool to evaluate vestibular function in children and should be used as the gold standard in pediatric vestibular assessment.

A spherical harmonics intensity model for 3D segmentation and 3D shape analysis of heterochromatin foci.

The genome is partitioned into regions of euchromatin and heterochromatin. The organization of heterochromatin is important for the regulation of cellular processes such as chromosome segregation and gene silencing, and their misregulation is linked to cancer and other diseases. We present a model-based approach for automatic 3D segmentation and 3D shape analysis of heterochromatin foci from 3D confocal light microscopy images. Our approach employs a novel 3D intensity model based on spherical harmonics, which analytically describes the shape and intensities of the foci. The model parameters are determined by fitting the model to the image intensities using least-squares minimization. To characterize the 3D shape of the foci, we exploit the computed spherical harmonics coefficients and determine a shape descriptor. We applied our approach to 3D synthetic image data as well as real 3D static and real 3D time-lapse microscopy images, and compared the performance with that of previous approaches. It turned out that our approach yields accurate 3D segmentation results and performs better than previous approaches. We also show that our approach can be used for quantifying 3D shape differences of heterochromatin foci.