Biology subjects

Soto, X.

Publications and source records attributed to Soto, X..

3 recordsLinked to original sources

bioRxiv2022

Cell coupling compensates for changes in single-cell Her6 dynamics and provides phenotypic robustness

her6 is a zebrafish ortholog of Hes1, known for its role in maintaining neural progenitors during neural development. Here, we characterise the population-level effect of altering Her6 protein expression dynamics at the single-cell level in the embryonic zebrafish telencephalon. Using an endogenous Her6:Venus reporter and 4D single-cell tracking, we show that Her6 oscillates in neural telencephalic progenitors and that fusion of a protein destabilisation domain (PEST) to Her6:Venus alters its expression dynamics causing most cells to downregulate Her6 prematurely. However, in PEST mutants, a higher proportion of cells exhibit Her6 oscillations and while expression is reduced in most cells, some cells express Her6 at wild-type levels resulting in increased heterogeneity of Her6 expression in the population. Despite the profound differences in the single-cell Her6 dynamics, differentiation markers do not exhibit major differences early on, while an increase in differentiation is observed at later developmental stages (vglut2a, gad1 and gad2). At the same time, at late stage the overall size of the telencephalon remains the same. Computational modelling that simulates changes in Her6 protein stability reveals that the increase in population Her6 expression heterogeneity is an emergent property of finely tuned Notch signalling coupling between single cells. Our study suggests that such cell coupling provides a compensation strategy whereby a normal phenotype is maintained while single-cell dynamics are abnormal, although the limit of this compensation is reached at late developmental stages. We conclude that in the neural progenitor population, cell coupling controls Her6 expression heterogeneity and in doing so, it provides phenotypic robustness when individual cells lose Her6 expression prematurely.

developmental biology↗

bioRxiv2020

Sequential onset and concurrent expression of miR-9 genomic loci in single cells contributes to the temporal increase of mature miR-9 in zebrafish neurogenesis

MicroRNAs (miRs) have important quantitative roles in tuning dynamical gene expression. Hes/Her transcription factor dynamics are sensitive to the increasing amount of miR-9 in the cell, transitioning from noisy high-level expression to oscillatory expression and then to downregulation. However, the mechanism by which miR-9 is quantitatively controlled is not known. In vertebrates, several distinct genomic loci produce the same mature miR-9, but the functional significance of multiple primary transcripts remains unknown. Here, we show that the amount of mature miR-9 increases during zebrafish neurogenesis in a sharp stepwise manner. We characterize the spatiotemporal profile of 7 distinct pri-mir-9s and show that they are sequentially expressed during hindbrain neurogenesis. Quantitative analysis of expression at the single-cell level, shows that expression of late-onset pri-mir-9-1 is added on, rather than replacing the expression of early onset pri-mir-9-4 and 9-5. Mutating the late-onset pri-mir-9-1 with CRISPR/Cas9 prevents the developmental increase of mature miR-9 and reduces late neuronal differentiation. Finally, we use mathematical modelling to explore possible benefits of a stepwise increase of miR-9 over a linear increase. We find that an adaptive network containing Her6 can be insensitive to a linear increase in miR-9 and show that such adaptation can be overcome by step-wise increases of miR-9. In conclusion, our work suggests that a sharp stepwise increase of mature miR-9 is contributed by sequential temporal activation of distinct loci. This may be a strategy to overcome adaptation and facilitate a transition to a new state of Her6 dynamics or level.

developmental biology↗

bioRxiv2019

miR-9 mediated noise optimization of the her6 oscillator is needed for cell state progression in the Zebrafish hindbrain

Ultradian oscillations of key transcription factors, such as members of the Hes family, are thought to be important in Neural Progenitor Cell (NPC) maintenance and miR-9 acts as a tuner of these oscillations in vitro. However, the existence and the role of such dynamic oscillatory expression in vivo is poorly understood. Here, we have generated a Zebrafish CRISPR knock-in Her6::venus fusion (Hes1 orthologue) to study endogenous dynamic gene expression in the embryonic hindbrain. We show that Her6 undergoes a transition from irregular, noisy, fluctuations to periodic oscillations as neurogenesis proceeds. In the absence of miR-9 input, noise in the Her6 oscillator increases and NPCs are unable to transit away from an intermediary state where they co-express progenitor and early differentiation markers. Thus, Her6 oscillations are facilitated by noise optimization mediated by miR-9 and this noise-tuning step is functionally important for cells to transition to differentiation.

developmental biology↗