A dynamic, spatially periodic, micro‐pattern of HES5 underlies neurogenesis in the mouse spinal cord

Abstract

Ultradian oscillations of HES Transcription Factors (TFs) at the single-cell level enable cell state transitions. However, the tissuelevel organisation of HES5 dynamics in neurogenesis is unknown. Here, we analyse the expression of HES5 ex vivo in the developing mouse ventral spinal cord and identify microclusters of 4-6 cells with positively correlated HES5 level and ultradian dynamics. These microclusters are spatially periodic along the dorsoventral axis and temporally dynamic, alternating between high and low expression with a supra-ultradian persistence time. We show that Notch signalling is required for temporal dynamics but not the spatial periodicity of HES5. Few Neurogenin 2 cells are observed per cluster, irrespective of high or low state, suggesting that the microcluster organisation of HES5 enables the stable selection of differentiating cells. Computational modelling predicts that different cell coupling strengths underlie the HES5 spatial patterns and rate of differentiation, which is consistent with comparison between the motoneuron and interneuron progenitor domains. Our work shows a previously unrecognised spatiotemporal organisation of neurogenesis, emergent at the tissue level from the synthesis of single-cell dynamics.

Dynamic switching of lateral inhibition spatial patterns

“…The inclusion of DBP in the model resulted in a region of parameter space being identified where dynamic spatial patterning occurs, indicating that with sufficient and regular perturbation, high and low states generated by the underlying Notch LI circuit can be dynamically switched and reorganized. In addition, nested dynamics of ultradian oscillations on top of the larger amplitude switching dynamics were observed in the model-generated single-cell time traces (figure 9), similar to that observed ex vivo [14]. One aspect that remains unclear due to experimental limits of the observation time of the ex vivo slices, is the regularity of switching.…”

“…where D thresh is the differentiation threshold (set as the population mean expression), and R is the rate of differentiation. For further details on the differentiation algorithm, see [14].…”

Signalling dynamics in embryonic development

“…When pro-neural genes are stabilized and Hes genes down-regulated, neural differentiation is initiated ( Figure 3B ). Similar oscillation dynamics of Hes5 have been observed in the developing spinal cord [ 75 , 76 ]. To test the functional significance of Hes dynamics in regulating cell behaviour, Imayoshi et al generated an optogenetic system to modulate Ascl1 expression in cells by light pulses [ 4 , 77 ].…”

A lateral protrusion latticework connects neuroepithelial cells and is regulated during neurogenesis

“…S7 " type="url"/> ). One possibility is that lateral protrusions (which with their filopodia radially contact cells several endfeet away) facilitate cell–cell coupling within cell micro-clusters, which have recently been shown to exhibit synchronous Hes gene (Notch signalling) oscillations, and so may serve to regulate neuron production ( Biga, 2021 ). Indeed, a role in local coordination of cell signalling is consistent with lateral protrusion withdrawal in newborn neurons, which might then experience reduced signalling from neighbouring cells, while subsequently delivering Notch ligand via adherens junctions ( Hatakeyama et al, 2014 ; Falo-Sanjuan and Bray, 2021 ).…”