The neurogenic fate of the hindbrain boundaries relies on Notch-dependent asymmetric cell divisions

Abstract

The generation of cell diversity in the central nervous system occurs during embryogenesis and requires a precise balance between stem cell proliferation, neuronal commitment to specific fates, and further differentiation. Understanding the cellular and molecular mechanisms regulating this balance in the embryonic brain is challenging. Here we reveal how the neurogenic capacity in the hindbrain is differently allocated to distinct domains over time, and how the boundary cells undergo a functional transition to become neurogenic during zebrafish hindbrain segmentation. By generating a CRISPR-based knock-in transgenic line to specifically label the boundary cell population, we tracked their derivatives over time and followed their behavior, allowing us to identify how asymmetric cell divisions arise and to reconstruct the trajectories of the boundary derivatives through the progenitor and differentiated domains. The behavioral switch in boundary cells is triggered by the onset of Notch signaling, based on lateral inhibition at the dorsoventral level. Our findings reveal that distinct neurogenic phases take place during hindbrain growth and suggest that boundary cells contribute to refine the final number, identity, and proportion of neurons in the brain.

A quantitative characterization of early neuron generation in the developing zebrafish telencephalon

“…Moreover, such studies have demonstrated that individual neural progenitor undergo probabilistic and deterministic decisions in generating neuron and glial cell diversity (Gao et al, 2014;Llorca et al, 2019). Similar studies have been performed in zebrafish hindbrain and retina to elucidate the rules and molecular regulators governing NPC lineage decisions and how NPC competence to generate diverse cell types changes as development proceeds (Boije et al, 2015;Hevia et al, 2021;Nerli et al, 2022;Zhao et al, 2021). Moreover, studies using live imaging microscopy can provide valuable insights into the mechanisms underlying asymmetric versus symmetric division modes (Clark et al, 2021;Kressmann et al, 2015;Nerli et al, 2020).…”

“…described for areas of the zebrafish nervous system such as the hindbrain, spinal cord and retina (Boije et al, 2015;He et al, 2012;Hevia et al, 2021;Kimura et al, 2008;Nerli et al, 2022;Satou et al, 2012). In this experimental work, we extend the existing body of work with an quantitative characterization of the first wave of neurogenesis in the developing zebrafish telencephalon using machine-learning based nuclear segmentation and clonal analysis methods.…”

“…Despite the advances made in understanding how the production of neuronal diversity from embryonic NPCs is regulated (Ge et al, 2022;Lodato and Arlotta, 2015), our understanding of the molecular and cell biological mechanisms underlying individual NPC division mode and fate decisions is limited. For instance, studies using various NPC lineage-tracing methods have demonstrated that there is remarkable heterogeneity in the division modes used by individual NPCs in the vertebrate nervous system (Dong et al, 2012;Gao et al, 2014;Gomes et al, 2011;He et al, 2012;Hevia et al, 2021;Llorca et al, 2019). Also, it is not clear whether the embryonic NPCs present at the onset of neurogenesis are equipotent in their ability to produce the different types of neurons (Ge et al, 2022;Zechner et al, 2020).…”

The Symmetry of Neural Stem Cell and Progenitor Divisions in the Vertebrate Brain

“…For instance, in the zebrafish and rat retina, tracking of individual clones through time-lapse imaging with cell fate markers shows high variability in the clonal size and composition of the lineages generated by individual NPCs ( Figure 1G , Gomes et al, 2011 ; He et al, 2012 ). Similarly, live imaging of NPCs in the developing zebrafish telencephalon and hindbrain show heterogeneity in the NPC division modes present at neurogenic stages ( Dong et al, 2012 ; Hevia et al, 2021 ). Intriguingly, in the zebrafish retina, the probabilities for retinal NPCs to undergo P-P, P-N or N-N divisions change over time ( Figure 1G ).…”

The Digital 3D-Atlas MAKER (DAMAKER): a dynamic and expandable digital 3D-tool for monitoring the temporal changes in tissue growth during hindbrain morphogenesis

“…This morphogenetic process is accompanied with the initial neuronal differentiation, which starts prior 24 hours post-fertilization (hpf) with a pronounced increase from 30 hpf onwards (Voltes et al, 2019). Neuronal differentiation involves changes in cell proliferative capacity and an extraordinary displacement of neurons from their birth site, and occurs while other dramatic changes take place, such as the generation of the brain ventricle (Belzunce et al, 2020; Gutzman et al, 2008; Hevia et al, 2021; Lyons et al, 2003). Although previous work evoked the importance of the order of neuronal differentiation in ascribing final neuronal position within specific circuits (Kinkhabwala et al, 2011; Pujala and Koyama, 2019; Wan et al, 2019), little is known about the role of the neuronal birthdate in the final organization of differentiated neurons within the hindbrain.…”