Biology subjects

Towbin, B. D.

Publications and source records attributed to Towbin, B. D..

4 recordsLinked to original sources

bioRxiv2023

Learning accelerates the evolution of slow aging but obstructs negligible senescence

BackgroundFor most animals, intrinsic senescence-induced mortality increases with age, while deaths from extrinsic threats, such as predation or accidents, decline during development as individuals grow and mature. Age-dependent modulation of extrinsic mortality is known to influence the evolution of aging, yet how the timing of mortality shapes evolutionary forces remains poorly understood. ResultsTo address this, we developed two complementary mathematical models that integrate survival benefits arising during development with the progressive increase in mortality associated with senescence. Agent-based simulations and deterministic analyses revealed a strong and consistent influence of the timing of developmental survival benefits on their evolutionary impact: early-life survival benefits reduced the selection for slower aging, while late-acting benefits enhanced it. This difference arises because early-life benefits more strongly accelerate population growth than late-life benefits, diminishing the relative evolutionary advantage of increased longevity. ConclusionsOur results underscore the importance of mortality timing in the evolution of aging and provide a theoretical framework for connecting developmental trajectories to aging dynamics.

evolutionary biology↗

bioRxiv2022

Ultra-sensitive coupling between organ growth and size by YAP-1 ensures uniform body plan proportions in C. elegans

Imbalance between the growth rate of different organs can amplify to large deviations of their size proportions during development. We show that, for the C. elegans pharynx, such size divergence is prevented by reciprocal coordination of pharyngeal growth with other tissues. Live imaging of hundreds of individuals revealed that small pharynxes grow more rapidly than large pharynxes, catching up in volume during development. Moreover, pharynx-to-body size proportions were robust to even strong tissue-specific inhibition of mTORC1 and insulin signalling. Tissue-specific depletion of these pathways slowed-down the growth of the respective tissue and additionally triggered a systemic growth response that ensured appropriate organ size proportions. By mathematical modelling, we show that the conservation of proportions requires a bi-directional ultra-sensitive coupling of body growth and pharynx size that cannot be explained by a reduction of food uptake alone. Instead, organ growth coordination requires regulation by the mechano-transducing transcriptional co-activator YAP/yap-1. Knock-down of yap-1 makes animals sensitive to tissue-specific inhibition mTORC1 inhibition, causing a disproportionate pharynx and developmental arrest. Our data suggests that mechano-transduction tightly coordinates organ growth during C. elegans development to ensure the uniformity of body plan proportions among individuals.

developmental biology↗

bioRxiv2022

The interplay between metabolic stochasticity and regulation in single E. coli cells

Metabolism is inherently stochastic at the cellular level. Whether cells actively regulate processes in response to these random internal variations is a fundamental problem that remains unaddressed, yet critical to understanding biological homeostasis. Here, we show that in E. coli cells, expression of the main catabolic enzymes is continuously adjusted in response to metabolic fluctuations under constant external conditions. This noise feedback is performed by the cAMP-CRP system, which controls transcription of the catabolic enzymes by modulating concentrations of the second messenger cAMP upon changes in metabolite abundance. Using time-lapse microscopy, genetic constructs that selectively disable cAMP-CRP noise feedback, and mathematical modelling, we show how fluctuations circulate through this hybrid metabolic-genetic network at sub cell-cycle timescales. This circulation of stochastic fluctuations is explained by four distinct noise propagation modes, one of which describes the continuous cAMP-CRP regulation. The model successfully predicts how noise circulation is impacted by C-sector under and over-expression. The results raise the question whether the cAMP-CRP system, as well as other metabolic regulation mechanisms, have evolved to manage internal metabolic fluctuations in addition to external growth conditions. We conjecture that second messengers may broadly function to control metabolic stochasticity and achieve cellular homeostasis.

systems biology↗

bioRxiv2021

A folder mechanism ensures size uniformity among C. elegans individuals by coupling growth and development

Animals increase by orders of magnitude in their volume during development. Hence, even small differences in the growth rates between individuals could generate large differences in their adult body size. Yet, such volume divergence among individuals is usually not observed in nature. We combined theory and experiment to understand the mechanisms of body size uniformity. Using live imaging, we measured the volume growth of hundreds of individuals of C. elegans over the entire span of their postembryonic development. We find that C. elegans grows exponentially in volume with a coefficient of variation of the growth rate of [~]7%, but that individuals diverge much less in volume than expected from this heterogeneity. The mechanism counteracting size divergence does not involve size thresholds for developmental milestones. Instead, an inverse coupling of the growth rate and the duration of development produces a constant volume fold change per larval stage. The duration of larval stages of C. elegans is determined by the period of a developmental oscillator. Using mathematical modelling, we show that an anti-correlation between the growth rate and the oscillatory period emerges as an intrinsic property of a genetic oscillator. We propose that the robustness of body volume fold change is a hard-wired characteristic of the oscillatory circuit and does not require elaborate mechanisms of size control by cellular signalling. Indeed, the coupling of growth and development was unaltered by mutation of canonical pathways of growth control. This novel concept of size homeostasis may broadly apply to other multicellular systems controlled by genetic oscillators.

developmental biology↗