Biology subjects

Billard, B.

Publications and source records attributed to Billard, B..

3 recordsLinked to original sources

bioRxiv2025

Adaptation of eukaryotic membrane homeostasis to species-specific cellular lipid landscapes

The physicochemical properties of biological membranes must be maintained within a range compatible with cellular physiology. In the face of external perturbations, membrane lipid homeostasis mechanisms sense and control membrane features. How such mechanisms evolve to function in organisms with different cellular lipid make-up is unknown. Here, we address this fundamental question by exploiting the natural divergence in membrane lipid composition between the related fission yeasts S. pombe and S. japonicus. Using lipidomics and transcriptomics, we show that the activity of the membrane-bound transcriptional activator Mga2, which regulates the {Delta}-9 desaturase Ole1 expression, is set to sense distinct levels of membrane unsaturation in the two species. Through retro-engineering and physiological experiments, we identify an evolutionary divergent but functionally constrained element within the juxtamembrane region of Mga2, which fine-tunes its performance to species-specific lipid composition. Our experiments indicate that high baseline expression of ole1, set by cis-regulatory elements in its upstream non-coding region, has redefined the dynamic range of Mga2 activation in S. pombe, supporting high lipidome unsaturation. Our work explores an "experiment of nature" to highlight the broad principles underlying the organisation and evolution of membrane homeostasis, which should be applicable to other genetic networks supporting cellular homeostatic processes.

cell biology↗

bioRxiv2023

Engineering heterothallic strains in fission yeast

In poor nitrogen conditions, fission yeast cells mate, undergo meiosis and form spores that are resistant to deleterious environments. Natural isolates of Schizosaccharomyces pombe are homothallic. This allows them to naturally switch between the two h- and h+ mating types with a high frequency, thereby ensuring the presence of both mating partners in a population of cells. However, alteration of the mating type locus can abolish mating type switching or reduce it to a very low frequency. Such heterothallic strains have been isolated and are common in research laboratories due to the simplicity of their use for Mendelian genetics. In addition to the standard laboratory strains, a large collection of natural S. pombe isolates is now available, representing a powerful resource for investigating the genetic diversity and biology of fission yeast. However, most of these strains are homothallic, and only tedious or mutagenic strategies have been described to obtain heterothallic cells from a homothallic parent. Here, we describe a simple approach to generate heterothallic strains. It takes advantage of an alteration of the mating type locus that was previously identified in a mating type switching-deficient strain and the CRISPR-Cas9 editing tool, allowing for a one-step engineering of heterothallic cells with high efficiency. Take away points- Conventional methods for obtaining heterothallic fission yeast strains are inefficient - We implemented a streamlined genetic editing approach to engineer heterothallism - All fission yeast isolates reported in Jeffares et al. 2015 can be engineered - This method enhances the exploration of genetic diversity in wild fission yeast

genetics↗

bioRxiv2022

Higher-order epistasis shapes natural variation in germ stem cell niche activity

SummaryNatural quantitative variation in developmental processes must be driven by allelic variation. Yet, the genotype-phenotype relationships underlying developmental system variation are understudied due to their inherent complexity. Taking advantage of the simple Caenorhabditis elegans germline stem cell system, we characterized natural differences in the germ stem cell niche activity of two distinct wild isolates--measured as differences in germline progenitor zone (PZ) size. Through quantitative trait locus (QTL) analysis, we detected multiple candidate causal loci, including two large-effect QTL on chromosomes II and V. Resolving the chromosome V QTL, we show that the isolate with a smaller PZ exhibits a unique 148 bp deletion in the promoter region of the Notch ligand, lag-2, a central signal promoting germ stem cell fate and proliferation. As predicted, introducing this deletion into the isolate with a large PZ resulted in a smaller PZ. Unexpectedly, re-introducing the deleted ancestral sequence in the isolate with a smaller PZ further reduced PZ size. Using allelic replacement lines, we show that these contradictory phenotypic effects are due to epistatic interactions among the lag-2 promoter, the chromosome II QTL, and additional loci in the genome. Although the lag-2 deletion appeared to explain natural variation in germ stem cell niche activity, its effects across multiple genetic backgrounds were unpredictable due to higher-order epistasis. Studying the genetic architecture of quantitative developmental systems without taking into account its natural variation may be misleading, emphasizing the need for a better integration of developmental and quantitative genetics.

genetics↗