Biology subjects

Merrow, M.

Publications and source records attributed to Merrow, M..

6 recordsLinked to original sources

bioRxiv2024

Desynchronization between timers provokes transient arrest during C. elegans development

In multicellular organisms, development entails the progression of diverse cellular processes that need to be temporally coordinated. During C. elegans postembryonic development, the events of molting and cell divisions progress in parallel during four larval stages and are modulated by external cues such as temperature and nutrient availability. While seam cell divisions occur predominantly before ecdysis of the cuticle, the order of the events can change, suggesting that they are controlled by independent mechanisms. Here, we have analyzed the impact of reduced insulin signaling in molting and in stage-specific cell divisions. We find that reduced insulin signaling in the daf-2(e1370) allele delays both of these events but has a larger impact on the timing of cell divisions, thus increasing the desynchrony between the events. The relative delay in seam cell divisions leads to a delay in the initiation of the subsequent stage of the molting program, providing a mechanism for resynchronization of developmental processes to the beginning of the larval stages.

developmental biology↗

bioRxiv2021

A Unified Model for Entrainment by Circadian Clocks: Dynamic Circadian Integrated Response Characteristic (dCiRC)

Circadian rhythm is a ubiquitous phenomenon, and it is observed in all biological kingdoms. In nature, their primary characteristic or phenotype is the phase of entrainment. There are two main hypotheses related to how circadian clocks entrain, parametric and non-parametric models. The parametric model focuses on the gradual changes of the clock parameters in response to the changing ambient condition, whereas the non-parametric model focuses on the instantaneous change of the phase of the clock in response to the zeitgeber. There are ample empirical data supporting both models. However, only recently has a unifying model been proposed, the circadian integrated response characteristic (CiRC). In the current study, we developed a system of ordinary differential equations, dynamic CiRC (dCiRC), that describes parameters of circadian rhythms and predicts the phase of entrainment in zeitgeber cycles. dCiRC mathematically extracts the underlying information of velocity changes of the internal clock that reflects the parametric model and the phase shift trajectory that reflects the non-parametric model from phase data under entraining conditions. As a proof of concept, we measured clock parameters of 26 Neurospora crassa ecotypes in both cycling and constant conditions using dCiRC. Our data showed that the morning light shortens the period of the clock while the afternoon light lengthens it. We also found that individual ecotypes have different strategies of integrating light effects to accomplish the optimal phase of entrainment, a model feature that is consistent with our knowledge of how circadian clocks are organized and encoded. The unified model dCiRC will provide new insights into how circadian clocks function under different zeitgeber conditions. We suggest that this type of model may be useful in the advent of chronotherapies.

systems biology↗

bioRxiv2021

Differential regulation of developmental stages supports a linear model for C. elegans postembryonic development

The repetitive nature of C. elegans postembryonic development is considered an oscillatory process, a concept that has gained traction from regulation by a circadian clock gene homolog. Nevertheless, each larval stage has a defined duration and entails specific events. We have measured the duration of each stage of development for over 2,500 larvae, under varied environmental conditions known to alter overall developmental rate. Our results show that distinct developmental stages respond differently to environmental perturbations, including changes in temperature, in food quantity and quality, and amount of insulin signaling. Furthermore, our high-resolution measurement of the effect of temperature on the stage-specific duration of development has unveiled novel features of temperature dependence in C. elegans postembryonic development. Altogether, our results support a model of linear progression of C. elegans development, with the duration of each stage determined by a unique program.

developmental biology↗

bioRxiv2021

Mechanisms Underlying the Complex Dynamics of Temperature Entrainment by a Circadian Clock

Autonomously oscillating circadian clocks resonate with daily environmental (zeitgeber) rhythms to organize physiology around the solar day. While entrainment properties and mechanisms have been studied widely and in great detail for light-dark cycles, entrainment to daily temperature rhythms remains poorly understood despite that they are potent zeitgebers. Here we investigate the entrainment of the chronobiological model organism Neurospora crassa, subject to thermocycles of different periods and fractions of warm versus cold phases, mimicking seasonal variations. Depending on the properties of these thermocycles, regularly entrained rhythms, period-doubling (frequency demultiplication) but also irregular aperiodic behavior occurs. We demonstrate that the complex nonlinear phenomena of experimentally observed entrainment dynamics can be understood by molecular mathematical modeling. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=152 SRC="FIGDIR/small/441752v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@17494b0org.highwire.dtl.DTLVardef@cdd47dorg.highwire.dtl.DTLVardef@1395d01org.highwire.dtl.DTLVardef@1092092_HPS_FORMAT_FIGEXP M_FIG C_FIG

systems biology↗

bioRxiv2018

Prolonged quiescence delays somatic stem cell-like division in Caenorhabditis elegans and is controlled by insulin signalling

Cells can enter quiescence in adverse conditions and resume proliferation when the environment becomes favourable. Prolonged quiescence comes with a cost, reducing proliferation potential and survival. Interestingly, cellular quiescence also occurs in normal development, with many cells spending most of their lifetime at this state. Elucidating the mechanisms involved in surviving long-term quiescence and in maintenance of cellular proliferation potential will contribute to a better understanding of the process of tissue regeneration. Developmental arrest of C. elegans at the L1 stage is an emerging model for the study of cellular quiescence and reactivation. During arrest, L1 larvae undergo a process that shares phenotypic hallmarks with the ageing of the adult. Interestingly, insulin signalling, a prominent pathway in the regulation of ageing, also balances cell proliferation and activation of stress resistance pathways during quiescence, becoming a candidate regulator of proliferation potential. Here we report that prolonged L1 quiescence delays reactivation of blast cell divisions in C. elegans, leading to a delay in the initiation of postembryonic development. This delay is accompanied by increased inter-individual variability. We propose that the delay in cell division results from the decline that animals suffer during L1 arrest. To that end, we show that insulin signalling modulates the rate of L1 ageing, affecting proliferative potential after quiescence. These findings support that the insulin signalling pathway has a comparable role in L1 arrest to that in ageing adults. Furthermore, we show that variable yolk provisioning to the embryos as a consequence of maternal age is one of the sources of inter-individual variability in recovery after quiescence of genetically identical animals. Taken together, these results support the relevance of L1 arrest as a model to study in vivo proliferation after quiescence and to understand the mechanisms for maintenance of proliferation potential.

developmental biology↗

bioRxiv2018

PREMONition: An algorithm for predicting the circadian clock-regulated molecular network

A transcriptional feedback loop is central to clock function in animals, plants and fungi. The clock genes involved in its regulation are specific to - and highly conserved within - the kingdoms of life. However, other shared clock mechanisms, such as phosphorylation, are mediated by proteins found broadly among living organisms, performing functions in many cellular sub-systems. Use of homology to directly infer involvement/association with the clock mechanism in new, developing model systems, is therefore of limited use. Here we describe the approach PREMONition, PREdicting Molecular Networks, that uses functional relationships to predict molecular circadian clock associations. PREMONition is based on the incorporation of proteins encoded by known clock genes (when available), rhythmically expressed clock-controlled genes and non-rhythmically expressed but interacting genes into a cohesive network. After tuning PREMONition on the networks derived for human, fly and fungal circadian clocks, we deployed the approach to predict a molecular clock network for Saccharomyces cerevisiae, for which there are no readily-identifiable clock gene homologs. The predicted network was validated using gene expression data and a growth assay for sensitivity to light, a zeitgeber of circadian clocks of most organisms. PREMONition may be used to identify candidate clock-regulated processes and thus candidate clock genes in other organisms.

bioinformatics↗