Dissecting Cell Lineage Specification and Sex Fate Determination in Gonadal Somatic Cells Using Single-Cell Transcriptomics

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The UK cellular microbiology network: Exploring the host‐bacterial interface

The UK Cellular Microbiology Network held its inaugural conference in February 2019. This stimulating day of scientific exchange will be the first of many, its organisers hope.     

Type I Interferon Controls Propagation of Long Interspersed Element-1

Type I interferons (IFN) including IFNα and IFNβ are critical for the cellular defense against viruses. Here we report that increased levels of IFNβ were found in testes from mice deficient in MOV10L1, a germ cell-specific RNA helicase that plays a key role in limiting the propagation of retrotransposons including Long Interspersed Element-1 (LINE-1). Additional experiments revealed that activation of LINE-1 retrotransposons increases the expression of IFNβ and of IFN-stimulated genes. Conversely, pretreatment of cells with IFN suppressed the replication of LINE-1. Furthermore, the efficacy of LINE-1 replication was increased in isogenic cell lines harboring inactivating mutations in diverse elements of the IFN signaling pathway. Knockdown of the IFN receptor chain IFNAR1 also stimulated LINE-1 propagation in vitro. Finally, a greater accumulation of LINE-1 was found in mice that lack IFNAR1 compared with wild type mice. We propose that LINE-1-induced IFN plays an important role in restricting LINE-1 propagation and discuss the putative role of IFN in preserving the genome stability.     

Integrative Conjugative Elements Are Widespread in Field Isolates of Mycoplasma Species Pathogenic for Ruminants

Comparative genomics have revealed massive horizontal gene transfer (HGT) between Mycoplasma species sharing common ruminant hosts. Further results pointed toward an integrative conjugative element (ICE) as an important contributor of HGT in the small-ruminant-pathogen Mycoplasma agalactiae. To estimate the prevalence of ICEs in ruminant mycoplasmas, we surveyed their occurrence in a collection of 166 field strains representing 4 (sub)species that are recognized as major pathogens. Based on available sequenced genomes, we first defined the conserved, minimal ICE backbone as composed of 4 coding sequences (CDSs) that are evenly distributed and predicted to be essential for ICE chromosomal integration-excision and horizontal transfer. Screening of the strain collection revealed that these 4 CDSs are well represented in ruminant Mycoplasma species, suggesting widespread occurrence of ICEs. Yet their prevalence varies within and among species, with no correlation found with the individual strain history. Extrachromosomal ICE forms were also often detected, suggesting that ICEs are able to circularize in all species, a first and essential step in ICE horizontal transfer. Examination of the junction of the circular forms and comparative sequence analysis of conserved CDSs clearly pointed toward two types of ICE, the hominis and spiroplasma types, most likely differing in their mechanism of excision-integration. Overall, our data indicate the occurrence and maintenance of functional ICEs in a large number of field isolates of ruminant mycoplasmas. These may contribute to genome plasticity and gene exchanges and, presumably, to the emergence of diverse genotypes within pathogenic mycoplasmas of veterinary importance.     

Influence of amylopectin structure and degree of phosphorylation on the molecular composition of potato starch lintners

Morphology, molecular structure, and thermal properties of potato starch granules with low to high phosphate content were studied as an effect of mild acid hydrolysis (lintnerization) to 80% solubilization at two temperatures (25 and 45°C). Light microscopy showed that the lintners contained apparently intact granules, which disintegrated into fragments upon dehydration. Transmission electron microscopy of rehydrated lintners revealed lacy networks of smaller subunits. The molecular composition of the lintners suggested that they largely consisted of remnants of crystalline lamellae. When lintnerization was performed at 45°C, the lintners contained more of branched dextrins compared to 25°C in both low and intermediate phosphate‐containing samples. High‐phosphate‐containing starch was, however, unaffected by temperature and this was probably due to an altered amylopectin structure rather than the phosphate content. After lintnerization, the melting endotherms were broad with decreased onset and increased peak melting temperatures. The relative crystallinity was lower in lintners prepared at 45°C. A hypothesis that combines the kinetics of lintnerization with the molecular and thermal characteristics of the lintners is presented. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 257–271, 2014.     

Co‐occurrence and phylogenetic distance in communities of mammalian ectoparasites: limiting similarity versus environmental filtering

Similarity between species plays a key role in the processes governing community assembly. The co‐occurrence of highly similar species may be unlikely if their similar needs lead to intense competition (limiting similarity). On the other hand, persistence in a particular habitat may require certain traits, such that communities end up consisting of species sharing the same traits (environmental filtering). Relatively little information exists on the relative importance of these processes in structuring parasite communities. Assuming that phylogenetic relatedness reflects ecological similarity, we tested whether the co‐occurrence of pairs of flea species (Siphonaptera) on the same host individuals was explained by the phylogenetic distance between them, among 40 different samples of mammalian hosts (rodents and shrews) from different species, areas or seasons. Our results indicate that frequency of co‐occurrence between flea species increased with decreasing phylogenetic distance between them in 37 out of 40 community samples, with 14 of these correlations being statistically significant. A meta‐analysis across all samples confirmed the overall trend for closely related species to co‐occur more frequently on the same individual hosts than expected by chance, independently of the identity of the host species or of environmental conditions. These findings suggest that competition between closely related, and therefore presumably ecologically similar, species is not important in shaping flea communities. Instead, if only fleas with certain behavioural, ecological and physiological properties can encounter and exploit a given host, and if phylogenetic relationships determine trait similarity among flea species, then a process akin to environmental filtering, or host filtering, could favour the co‐occurrence of related species on the same host.