Lopez, S. L. | Search bioRxiv

bioRxiv2020

Segregation of brain and organizer precursors is differentially regulated by Nodal signaling at blastula stage

The Blastula Chordin- and Noggin Expressing Center (BCNE) comprises animal-dorsal and marginal-dorsal cells of the amphibian blastula and contains the precursors of the brain and of the gastrula organizer. Previous findings suggested that the BCNE behaves as a homogeneous cell population that depends only on nuclear {beta}-catenin activity but does not require Nodal and segregates into its descendants later, during gastrulation. In this work, we analyzed if the BCNE is already compartmentalized at the blastula stage. In contrast to previous findings, we show that the BCNE does not behave as a homogeneous cell population in response to Nodal antagonists. In fact, we found that the chordin.1 expression in a marginal subpopulation of notochordal precursors indeed requires Nodal input. We also establish that an animal BCNE subpopulation of cells that express both, chordin.1 and sox2 (a marker of pluripotent neuroectodermal cells), and gives rise to most of the brain, persisted at blastula stage after blocking Nodal. Moreover, RT-qPCR analysis showed that chordin.1 and sox2 expression increased at blastula stage after blocking Nodal. Therefore, Nodal signaling is required to define a population of chordin.1+ cells and to restrict the recruitment of brain precursors within the BCNE as early as at blastula stage.

developmental biology↗

bioRxiv2019

Temporal and spatiotemporal perturbations in paced finger tapping point to a common mechanism for the processing of time errors

Paced finger tapping is a sensorimotor synchronization task where a subject is instructed to keep pace with an external metronome, as when following along with the beat of music, and the time differences (asynchronies) between each stimulus and its response are recorded. The usual way to study the underlying error correction mechanism is to make unexpected temporal perturbations to the stimuli sequence and then let the subject recover average synchronization. A critical but overlooked issue in traditional temporal perturbations, however, is that at the moment of perturbation two things change: both the stimuli period (a parameter) and the asynchrony (a variable). In terms of experimental manipulation, it would be desirable to have separate, independent control of parameter and variable values. In this work we perform paced finger tapping experiments combining simple temporal perturbations (tempo step change) and spatial perturbations with temporal effect (raised or lowered point of contact). In this way we decouple the parameter-and-variable confounding of traditional temporal perturbations and perform novel perturbations where either the parameter only changes or the variable only changes. Our results show nonlinear features like asymmetry and are compatible with the idea of a common mechanism for the correction of all types of asynchronies. We suggest taking this confounding into account when analyzing perturbations of any kind in finger tapping tasks but also in other areas of sensorimotor synchronization, like music performance experiments and paced walking in gait coordination studies.

neuroscience↗