Chauve, Laetitia et al. (2017) International Worm Meeting "Analysis of inter-individual transcriptional variability of stress response genes in C. elegans by high-throughput qRT-PCR in single worms."

Chauve, Laetitia, Vallejos, Catalina, Marioni, John, Casanueva, Olivia, Hastings, Janna

[International Worm Meeting, 2017]

Across species, it has been noted that lifespan is highly variable among individuals. Understanding the basis for such variability is crucial for personalized medicine where not the average population, but rather the individual is center stage. It is also crucial for the identification of new factors that that can have an impact for human ageing and health and that may have been missed by the analysis of population averages. Remarkably, lifespan is highly variable across C. elegans individuals, although they are genetically identical and reared in controlled environmental conditions. Individual nematodes will experience lifespans ranging over 20% of the population mean. Both genetic and environmental factors are known to control lifespan. The widespread phenotypic variability, however, may point at additional non-genetic factors influencing ageing. C. elegans lifespan is controlled by several genetic pathways, including Insulin-Like Signalling and Target Of Rapamycin. These longevity pathways converge, among other transcriptional targets, on stress response genes and molecular chaperones. Remarkably, inter-individual variability in stress response genes has consequences for the robustness to both genetic and environmental perturbations in Caenorhabditis elegans and correlates with lifespan and mutation penetrance (Rea at al., 2005, Casanueva et al., Science 2011). To monitor inter-individual variability in gene expression, we have established a high throughput quantitative real time PCR assay on single worms using nano-fluidic technology. We have also developed an integrative Bayesian statistical method to estimate biological variability from PCR datasets, while accounting for technical variability. This technique allows us to identify highly variable genes throughout ageing. Our aim is to understand the molecular basis of the recorded probabilistic nature of gene expression and to exploit inter-individual variability in gene expression as a method to study gene network architecture in a metazoan model organism.

Chauve, Laetitia et al. (2019) International Worm Meeting "Inter-individual variability in neuronal stress creates phenotypic variability."

Marioni, John, Hastings, Janna, Chauve, Laetitia, Biggins, Laura, Todtenhaupt, Pia, Murdoch, Sharlene, Vallejos, Catalina, Casanueva, Olivia

[International Worm Meeting, 2019]

We use isogenic C. elegans to study non-genetic influences on phenotypic heterogeneity. Heat shock proteins (hsps) are collectively controlled by the transcription factor HSF-1 and are essential to maintain protein-folding homeostasis. Despite their essentiality, previous works has shown that upon exposure to stress, hsp induction is variable across worms dictating an individual's ability to both cope with stress and to reproduce. The dose-sensitive and critical nature of these phenotypes for survival, prompted us to study inter-individual transcriptional variability under normal, unstressed conditions. We developed a sensitive high-throughput quantitative PCR method and incorporated a Bayesian statistical approach to accurately quantify inter-individual steady-state transcript variability in single worms. We find that hsp transcripts are highly variable across worms even in the absence of exogenous stress. Surprisingly we observed that in vivo, inter-individual variability stems primarily from head neurons (n-hsp). It has been previously shown that ectopic hsf-1 expression in head neurons (n-hsf-1) protects better against exogenous stress. We find a similar phenotype happens to individual worms with greater number of n-hsps under physiological conditions. In addition, we observe that the number of n-hsps is temperature sensitive, suggesting that neuronal stress could modulate adaptation to ambient temperatures. We find that n-hsps anti-correlate with fat desaturases, known to contribute unsaturated fatty acids (UFAs) to both fat storages and membranes. Negative regulation of UFAs is also caused by n-HSF-1, demonstrating causality. We have identified the neurons and the signals critical to relay information across tissues and propose a model where neurons act as a sensitive thermostat that orchestrates homeo-viscous adaptation. The variable activation of the thermostat at normal ambient temperatures creates phenotypic heterogeneity with potential adaptive value.