Zygotic contractility awakening during mouse preimplantation development

Actomyosin contractility is a major engine of preimplantation morphogenesis, which starts at the 8-cell stage during mouse embryonic development. Contractility becomes first visible with the appearance of periodic cortical waves of contraction (PeCoWaCo), which travel around blastomeres in an oscillatory fashion. How contractility of the mouse embryo becomes active remains unknown. We have taken advantage of PeCoWaCo to study the awakening of contractility during preimplantation development. We find that PeCoWaCo become detectable in most embryos only after the 2nd cleavage and gradually increase their oscillation frequency with each successive cleavage. To test the influence of cell size reduction during cleavage divisions, we use cell fusion and fragmentation to manipulate cell size across a 20-60 μm range. We find that the stepwise reduction in cell size caused by cleavage divisions does not explain the presence of PeCoWaCo or their accelerating rhythm. Instead, we discover that blastomeres gradually decrease their surface tensions until the 8-cell stage and that artificially softening cells enhances PeCoWaCo prematurely. Therefore, during cleavage stages, cortical softening awakens zygotic contractility before preimplantation morphogenesis.

Cortical waves mediate the cellular response to electric fields

The molecular mechanisms by which electric fields direct cell migration remain largely unknown, because the cortical waves of signal transduction and cytoskeletal activity that drive cell protrusions are comparable in size to the cells themselves. To address this problem, here, we employ electro-fused giant cells, which are considerably larger than these waves, and nanotopography, which decreases the lifetime of waves on the basal surface. We find that electric fields increase the wave area and lifetime in the region of the cell nearer the cathode, and bias the wave direction. We also notice that shorter-lived waves on nanotopography lead to a faster cell response to electrical-field reversal. Our findings indicate that the directions and durations of waves have a dominant effect on cellular response to electric fields.

Slow Cortical Waves via Cyclicity

Fine-grained information about dynamic structure of cortical networks is crucial in unpacking brain function. Here,we introduced a novel analytical method to characterize the dynamic interaction between distant brain regions,based on cyclicity analysis, and applied it to data from the Human Connectome Project. Resting-state fMRI time series are aperiodic and, hence, lack a base frequency. Cyclicity analysis, which is time-reparametrization invariant, is effective in recovering dynamic temporal ordering of such time series along a circular trajectory without assuming any time scale. Our analysis detected the propagation of slow cortical waves across thebrain with consistent shifts in lead-lag relationships between specific brain regions. We also observed short bursts of strong temporal ordering that dominated overall lead-lag relationships between pairs of regions in the brain, which were modulated by tasks. Our results suggest the possible role played by slow waves of ordered information between brain regions that underlie emergent cognitive function.

Spontaneous Traveling Cortical Waves Gate Perception in Awake Behaving Primates

Perceptual sensitivity varies from moment to moment. One potential source of variability is spontaneous fluctuations in cortical activity that can travel as a wave. Spontaneous traveling waves have been reported during anesthesia, but questioned as to whether they are relevant to waking cortical function. Using newly developed analytic techniques, we find spontaneous waves of activity in extrastriate visual cortex of awake marmosets (Callithrix jacchus). In monkeys trained to detect faint visual targets, the timing and position of spontaneous traveling waves, prior to target onset, predict the magnitude of evoked activity and the likelihood of detection. In contrast, spatially disorganized fluctuations of neural activity are much less predictive. These results reveal an important role for spontaneous traveling waves in sensory processing through modulating neural and perceptual sensitivity.One Sentence SummaryFluctuations in cortical activity often travel as waves, shape incoming sensory information, and affect conscious perception.