Choanoflagellates and the ancestry of neurosecretory vesicles

Neurosecretory vesicles are highly specialized trafficking organelles that store neurotransmitters that are released at presynaptic nerve endings and are, therefore, important for animal cell–cell signalling. Despite considerable anatomical and functional diversity of neurons in animals, the protein composition of neurosecretory vesicles in bilaterians appears to be similar. This similarity points towards a common evolutionary origin. Moreover, many putative homologues of key neurosecretory vesicle proteins predate the origin of the first neurons, and some even the origin of the first animals. However, little is known about the molecular toolkit of these vesicles in non-bilaterian animals and their closest unicellular relatives, making inferences about the evolutionary origin of neurosecretory vesicles extremely difficult. By comparing 28 proteins of the core neurosecretory vesicle proteome in 13 different species, we demonstrate that most of the proteins are present in unicellular organisms. Surprisingly, we find that the vesicular membrane-associated soluble N-ethylmaleimide-sensitive factor attachment protein receptor protein synaptobrevin is localized to the vesicle-rich apical and basal pole in the choanoflagellate Salpingoeca rosetta. Our 3D vesicle reconstructions reveal that the choanoflagellates S. rosetta and Monosiga brevicollis exhibit a polarized and diverse vesicular landscape reminiscent of the polarized organization of chemical synapses that secrete the content of neurosecretory vesicles into the synaptic cleft. This study sheds light on the ancestral molecular machinery of neurosecretory vesicles and provides a framework to understand the origin and evolution of secretory cells, synapses and neurons. This article is part of the theme issue ‘Basal cognition: multicellularity, neurons and the cognitive lens’

Colonial choanoflagellate isolated from Mono Lake harbors a microbiome

Choanoflagellates offer key insights into bacterial influences on the origin and early evolution of animals. Here we report the isolation and characterization of a new colonial choanoflagellate species, Barroeca monosierra, that, unlike previously characterized species, harbors a stable microbiome. B. monosierra was isolated from Mono Lake, California and forms large spherical colonies that are more than an order of magnitude larger than those formed by the closely related Salpingoeca rosetta. By designing fluorescence in situ hybridization probes from metagenomic sequences, we found that B. monosierra colonies are colonized by members of the halotolerant and closely related Saccharospirillaceae and Oceanospirillaceae, as well as purple sulfur bacteria (Ectothiorhodospiraceae) and non-sulfur Rhodobacteraceae. This relatively simple microbiome in a close relative of animals presents a new experimental model for investigating the evolution of stable interactions among eukaryotes and bacteria

Structural diversity of supercoiled DNA

By regulating access to the genetic code, DNA supercoiling strongly affects DNA metabolism. Despite its importance, however, much about supercoiled DNA (positively supercoiled DNA, in particular) remains unknown. Here we use electron cryo-tomography together with biochemical analyses to investigate structures of individual purified DNA min icircle topoisomers with defined degrees of supercoiling. Our results reveal that each topoisomer, negative or positive, adopts a unique and surprisingly wide distribution of three-dimensional conformations. Moreover, we uncover striking differences in how the topoisomers handle torsional stress. As negative supercoiling increases, bases are increasingly exposed. Beyond a sharp supercoiling threshold, we also detect exposed bases in positively supercoiled DNA. Molecular dynamics simulations independently confirm the conformational heterogeneity and provide atomistic insight into the flexibility of supercoiled DNA. Our integrated approach reveals the three-dimensional structures of DNA that are essential for its function

On the Front Line of Community-Led Air Quality Monitoring

In this chapter, we explore the potential of community-led air quality monitoring. Community-led air quality monitoring differs from top-down monitoring in many aspects: it is focused on community needs and interests and a local problem and, therefore, has a limited geographical coverage as well as limited temporal coverage. However, localised air quality monitoring can potentially increase the spatial and temporal resolution of air quality information if there is a suitable information-sharing mechanism in place: information from multiple community-led activities can be shared at the city scale and used to augment official information. At the core of the chapter, we provide a detailed experiential description of the process of urban air quality practice, from which we draw our conclusion. We suggest that accessible and reliable community-led air quality monitoring can contribute to the understanding of local environmental issues and improve the dialogue between local authorities and communities about the impacts of air pollution on health and urban and transport planning. Document type: Part of book or chapter of boo

Management information systems managing the digital firm, Ed. 11

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xxxv. 897 hal.; 26 c

Evolutionary and biological mechanisms underpinning chitin degradation in aquatic fungi

Fungal biology underpins major processes in ecosystems. The Chytridiomycota (chytrids) is a group of early-diverging fungi, many of which function in ecosystems as saprotrophs processing high molecular weight biopolymers, however the mechanisms underpinning chytrid saprotrophy are poorly understood. Genome sequences from representatives across the group and the use of model chytrids offers the potential to determine new insights into their evolution. In this study, we focused on the biology underpinning chitin saprotrophy, a common ecosystem function of aquatic chytrids. The genomes of chitinophilic chytrids have expanded inventories of glycoside hydrolase genes responsible for chitin processing, complemented with bacteria-like chitin-binding modules (CBMs) that are absent in other chytrids. In the model chitinophilic saprotroph Rhizoclosmatium globosum JEL800, the expanded repertoire of chitinase genes is diverse and almost half were detected as proteins in the secretome when grown with chitin. Predicted models of the secreted chitinases indicate a range of active site sizes and domain configurations. We propose that increased diversity of secreted chitinases is an adaptive strategy that facilitates chitin degradation in the complex heterologous organic matrix of the arthropod exoskeleton. Free swimming R. globosum JEL800 zoospores are chemotactic to the chitin monomer N-acetylglucosamine and accelerate zoospore development when grown with chitin. Our study sheds light on the underpinning biology and evolutionary mechanisms that have supported the saprotrophic niche expansion of some chytrids to utilise lucrative chitin-rich particles in aquatic ecosystems and is a demonstration of the adaptive capability of this successful fungal grou