Braendle C (2012) Curr Biol "Pheromones: evolving language of chemical communication in nematodes."

Braendle C

[Curr Biol, 2012]

New research reveals how the intricate repertoire of ascarosides--small molecules acting as multifaceted pheromones in the nematode worm Caenorhabditis elegans--has evolved in divergent nematode taxa occupying contrasted ecological niches.

Braendle C et al. (2006) Curr Biol "Sex determination: ways to evolve a hermaphrodite."

Braendle C, Felix MA

[Curr Biol, 2006]

Most species of the nematode genus Caenorhabditis reproduce through males and females; C. elegans and C. briggsae, however, produce self-fertile hermaphrodites instead of females. These transitions to hermaphroditism evolved convergently through distinct modifications of germline sex determination mechanisms.

Braendle C et al. (2008) Dev Cell "Plasticity and errors of a robust developmental system in different environments."

Braendle C, Felix MA

[Dev Cell, 2008]

Many developmental processes generate invariant phenotypes in a wide range of ecological conditions. Such robustness to environmental variation is a fundamental biological property, yet its extent, limits, and adaptive significance have rarely been assessed empirically. Here we tested how environmental variation affects vulval formation in Caenorhabditis nematodes. In different environments, a correct vulval pattern develops with high precision, but rare deviant patterns reveal the system's limits and how its mechanisms respond to environmental challenges. Key features of the apparent robustness are functional redundancy among vulval precursor cells and tolerance to quantitative variation in Ras, Notch, and Wnt pathway activities. The observed environmental responses and precision of vulval patterning vary within and between Caenorhabditis species. These results highlight the complex response of developmental systems to the environment and illustrate how a robust and invariant phenotype may result through cellular and molecular processes that are highly plastic--across environments and evolution.

Braendle C et al. (2010) PLoS Genet "Bias and evolution of the mutationally accessible phenotypic space in a developmental system."

Baer CF, Felix MA, Braendle C

[PLoS Genet, 2010]

Genetic and developmental architecture may bias the mutationally available phenotypic spectrum. Although such asymmetries in the introduction of variation may influence possible evolutionary trajectories, we lack quantitative characterization of biases in mutationally inducible phenotypic variation, their genotype-dependence, and their underlying molecular and developmental causes. Here we quantify the mutationally accessible phenotypic spectrum of the vulval developmental system using mutation accumulation (MA) lines derived from four wild isolates of the nematodes Caenorhabditis elegans and C. briggsae. The results confirm that on average, spontaneous mutations degrade developmental precision, with MA lines showing a low, yet consistently increased, proportion of developmental defects and variants. This result indicates strong purifying selection acting to maintain an invariant vulval phenotype. Both developmental system and genotype significantly bias the spectrum of mutationally inducible phenotypic variants. First, irrespective of genotype, there is a developmental bias, such that certain phenotypic variants are commonly induced by MA, while others are very rarely or never induced. Second, we found that both the degree and spectrum of mutationally accessible phenotypic variation are genotype-dependent. Overall, C. briggsae MA lines exhibited a two-fold higher decline in precision than the C. elegans MA lines. Moreover, the propensity to generate specific developmental variants depended on the genetic background. We show that such genotype-specific developmental biases are likely due to cryptic quantitative variation in activities of underlying molecular cascades. This analysis allowed us to identify the mutationally most sensitive elements of the vulval developmental system, which may indicate axes of potential evolutionary variation. Consistent with this scenario, we found that evolutionary trends in the vulval system concern the phenotypic characters that are most easily affected by mutation. This study provides an empirical assessment of developmental bias and the evolution of mutationally accessible phenotypes and supports the notion that such bias may influence the directions of evolutionary change.

Braendle C et al. (2008) Curr Top Dev Biol "Mechanisms and evolution of environmental responses in Caenorhabditis elegans."

Milloz J, Braendle C, Felix MA

[Curr Top Dev Biol, 2008]

We review mechanistic and evolutionary aspects of interactions between the model organism Caenorhabditis elegans and its environment. In particular, we focus on environmental effects affecting developmental mechanisms. We describe natural and laboratory environments of C. elegans and provide an overview of the different environmental responses of this organism. We then show how two developmental processes respond to changes in the environment. First, we discuss the development of alternative juvenile stages, the dauer and non-dauer larva. This example illustrates how development responds to variation in the environment to generate complex phenotypic variation. Second, we discuss the development of the C. elegans vulva. This example illustrates how development responds to variation in the environment while generating an invariant final phenotype.

Braendle C et al. (2009) J Biosci "The other side of phenotypic plasticity: a developmental system that generates an invariant phenotype despite environmental variation."

Felix MA, Braendle C

[J Biosci, 2009]

Understanding how the environment impacts development is of central interest in developmental and evolutionary biology. On the one hand, we would like to understand how the environment induces phenotypic changes (the study of phenotypic plasticity). On the other hand, we may ask how a development system maintains a stable and precise phenotypic output despite the presence of environmental variation. We study such developmental robustness to environmental variation using vulval cell fate patterning in the nematode Caenorhabditis elegans as a study system. Here we review both mechanistic and evolutionary aspects of these studies, focusing on recently obtained experimental results. First, we present evidence indicating that vulval formation is under stabilizing selection. Second, we discuss quantitative data on the precision and variability in the output of the vulval developmental system in different environments and different genetic backgrounds. Third, we illustrate how environmental and genetic variation modulate the cellular and molecular processes underlying the formation of the vulva. Fourth, we discuss the evolutionary significance of environmental sensitivity of this developmental system.

C Braendle et al. (2004) European Worm Meeting "FLEXIBILITY AND ROBUSTNESS OF VULVA DEVELOPMENT IN VARIABLE ENVIRONMENTS"

M Felix, C Braendle

[European Worm Meeting, 2004]

All organisms have to maintain great phenotypic stability (robustness) in the face of changes in their environment. To gain a better understanding of the mechanisms providing robustness, we study the developmental mechanisms underlying the expression of an invariant and reproducible phenotype: vulval cell fate specification in the nematode Caenorhabditis elegans. This cell patterning process is controlled by a network of tightly regulated and partially redundant signalling pathways (Ras/Notch/Wnt). The significance of these mechanisms is not fully understood, yet their properties, such as redundancy, may be important to maintain a correct vulva phenotype when development is perturbed. We have started to test this idea by studying vulva formation (of vulva mutants and wild type animals) in different environmental conditions (e.g. starvation, liquid culture, passing through the dauer stage). Such environmental conditions have previously been shown to affect the penetrance of several vulva mutations (Ferguson & Horvitz 1985, Battu et al. 2003, Moghal et al. 2003), indicating that vulval development is sensitive to environmental variation. We further aim to test whether pathway activation is differentially regulated in a context-dependent fashion, and to examine how such a differential regulation corresponds to changes in the precision of the vulval patterning process. If different environments alter the use of developmental mechanisms while maintaining precision of the vulva pattern, this would indicate that development exhibits flexibility, which serves to maintain phenotypic stability. This scenario would suggest that environmental variation plays a role in shaping and maintaining the mechanisms underlying vulva formation. We thus also aim to examine whether different C. elegans strains, potentially exhibiting different environmental histories, have evolved differences in the mechanisms controlling vulva development. References Ferguson & Horvitz (1985). Genetics: 110: 17-72.Battu et al.(2003). Development 130: 2567-2577. Moghal et al. (2003). Development 130: 4553-4566.

Poullet N et al. (2015) Methods Mol Biol "Sampling and Isolation of C. elegans from the Natural Habitat."

Poullet N, Braendle C

[Methods Mol Biol, 2015]

Wild populations of the model organism C. elegans allow characterization of natural genetic variation underlying diverse phenotypic traits. Here we provide a simple protocol on how to sample and rapidly identify C. elegans wild isolates. We outline how to find suitable habitats and organic substrates, followed by describing isolation and identification of C. elegans live cultures based on easily recognizable morphological characteristics, molecular barcodes and/or mating tests. This protocol uses standard laboratory equipment and requires no prior knowledge of C. elegans biology.

Felix MA et al. (2010) Curr Biol "The natural history of Caenorhabditis elegans."

Felix MA, Braendle C

[Curr Biol, 2010]

In the laboratory, the nematode Caenorhabditis elegans lives on the surface of nutrient agar in Petri dishes, feeding on a lawn of the uracil auxotroph strain OP50, an Escherichia coli mutant strain. This sentence sums up the fundamentals of C. elegans ecology, as most of us know it. While over 15,000 articles on diverse biological aspects of C. elegans attest to the worm's undisputable virtues as a major model organism, its biology in the wild remains mysterious. To properly interpret and fully understand the available wealth of genetic, molecular and other biological observations made in the laboratory, it will be important to know its natural history and to place the species in its ecological and evolutionary context. With the aim of connecting the discoveries that have been made about C. elegans biology to its 'real life', we shall discuss recent studies on the worm's natural habitat and population biology, and outline key issues in attaining a modern natural history of C. elegans.

Gimond C et al. (2022) Methods Mol Biol "Isolating Caenorhabditis elegans from the Natural Habitat."

Gimond C, Poullet N, Braendle C

[Methods Mol Biol, 2022]

Wild populations of the model organism C. elegans represent a valuable resource, allowing for genetic characterization underlying natural phenotypic variation. Here we provide a simple protocol on how to sample and rapidly identify C. elegans wild isolates. We outline how to find suitable habitats and organic substrates, followed by describing isolation and identification of C. elegans live cultures based on easily recognizable morphological characteristics, molecular barcodes, and mating tests. This protocol uses standard laboratory equipment and requires little prior knowledge of C. elegans biology.