Biology subjects

Ellis, P. J. I.

Publications and source records attributed to Ellis, P. J. I..

3 recordsLinked to original sources

bioRxiv2020

Myosin VI moves on nuclear actin filaments and supports long-range chromatin rearrangements

Nuclear myosin VI (MVI) enhances RNA polymerase II - dependent transcription, but the molecular mechanism is unclear. We used live cell single molecule tracking to follow individual MVI molecules inside the nucleus and observed micrometer-long motion of the motor. Besides static chromatin interactions lasting for tens of seconds, ATPase-dependent directed motion occurred with a velocity of 2 {micro}m/s. The movement was frequently interrupted by short periods of slow restricted diffusion and increased in frequency upon stimulation of transcription. Mutagenesis and perturbation experiments demonstrated that nuclear MVI motion is independent of dimerization and occurs on nuclear actin filaments, which we also observed by two-color imaging. Using chromosome paint to quantify distances between chromosomes, we found that MVI is required for transcription-dependent long-range chromatin rearrangements. Our measurements reveal a transcription-coupled function of MVI in the nucleus, where it actively undergoes directed movement along nuclear actin filaments. Motion is potentially mediated by cooperating monomeric motors and might assist in enhancing transcription by supporting long-range chromatin rearrangements.

cell biology↗

bioRxiv2018

Automated nuclear cartography reveals conserved sperm chromosome territory localization across 2 million years of mouse evolution

Measurements of nuclear organization in asymmetric nuclei in 2D images have traditionally been manual. This is exemplified by attempts to measure chromosome position in sperm samples, typically by dividing the nucleus into zones, and manually scoring which zone a FISH signal lies in. This is time consuming, limiting the number of nuclei that can be analyzed, and prone to subjectivity. We have developed a new approach for automated mapping of FISH signals in asymmetric nuclei, integrated into an existing image analysis tool for nuclear morphology. Automatic landmark detection defines equivalent structural regions in each nucleus, then dynamic warping of the FISH images to a common shape allows us to generate a composite of the signal within the entire cell population. Using this approach, we mapped the positions of the sex chromosomes and two autosomes in three mouse lineages (Mus musculus domesticus, Mus musculus musculus and Mus spretus). We found that in all three, chromosomes 11 and 19 tend to interact with each other, but are shielded from interactions with the sex chromosomes. This organization is conserved across 2 million years of mouse evolution.

genomics↗

bioRxiv2018

A high-throughput method for unbiased quantitation and categorisation of nuclear morphology

The physical arrangement of chromatin in the nucleus is cell type and species specific. This is particularly evident in sperm, in which most of the cytoplasm has been lost; the shape of the nucleus reflects the shape of the cell. Mice have distinctive falciform ( hook shaped) sperm heads and nuclei. Quantification of the differences in shape variation between mouse species and lines often relies on manual measurement and classification that leads to subjective results, making comparisons within and between samples difficult.\n\nWe have developed an analysis program for assessing the morphology of asymmetric nuclei, and characterised the sperm of mice from a range of inbred, outbred and wild-derived mouse lines. We find that laboratory lines have elevated sperm shape variability both within and between samples in comparison to wild-derived inbred lines, and that sperm shape in the F1 offspring of CBA and C57Bl6J lines is subtly affected by the direction of the cross.\n\nHierarchical clustering can distinguish distinct sperm shapes with greater efficiency and reproducibility than even experienced manual assessors. We quantified the range of morphological defects in the inbred BALB/c line, demonstrating we can identify different morphological subgroups. This approach has applications for studies of sperm development, infertility and toxicology.

genomics↗