Cambon, M. | Search bioRxiv

bioRxiv2018

Changes in rearing conditions rapidly modify gut microbiota structure in Tenebrio molitor larvae

The gut microbiota of multicellular organisms has been shown to play a key role in their host biology. In mammals, it has an invariant component, responsible for establishing a mutualistic relationship with the host. It also contains a dynamic fraction which facilitates adaptation in response to changes in the environment. These features have been well described in mammals, but little is known about microbiota stability or plasticity in insects. We assessed changes in microbiota composition and structure in a reared insect after a change in rearing conditions. We reared Tenebrio molitor (Coleoptera, Tenebrioninae) larvae for five days in soil samples from two river banks and analyzed their gut microbial communities by a metabarcoding technique, using the V3-V4 region of the 16S rRNA gene and the housekeeping gene gyrB. We found that soil-reared insects had a significantly more diverse microbiota than the control insects and that insects reared in soil from different sites had significantly different microbiota. We confirmed this trend by absolute quantification of the two mains fluctuating taxonomic groups: the Enterobacteriaceae family and the Pseudomonas genus, dominant in the soil-reared insects and in the control insects, respectively. Our results suggest the existence of a resident microbiota in T. molitor gut, but indicate that rearing changes can induce rapid and profound changes in the relative abundance of some of the members of this resident microbiota.

microbiology↗

bioRxiv2018

Analysis of the transcriptional logic governing differential spatial expression in Hh target genes

This work provides theoretical tools to analyse the transcriptional effects of certain biochemical mechanisms (i.e. affinity and cooperativity) that have been proposed in previous literature to explain the differential spatial expression of Hedgehog target genes involved in Drosophila development. Specifically we have focused on the expression of decapentaplegic and patched. The transcription of these genes is believed to be controlled by opposing gradients of the activator and repressor forms of the transcription factor Cubitus interruptus (Ci). This study is based on a thermodynamic approach, which provides expression rates for these genes. These expression rates are controlled by transcription factors which are competing and cooperating for common binding sites. We have made mathematical representations of the different expression rates which depend on multiple factors and variables. The expressions obtained with the model have been refined to produce simpler equivalent formulae which allow for their mathematical analysis. Thanks to this, we can evaluate the correlation between the different interactions involved in transcription and the biological features observed at tissular level. These mathematical models can be applied to other morphogenes to help understand the complex transcriptional logic of opposing activator and repressor gradients.\n\nAuthor summaryMorphogenic differentiation is a complex process that involves emission, reception and cellular response to different signals. It is well known that the same morphogenic signal can give rise to different cellular transcriptional responses that usually depend, among other factors, on transcription factors. In concordance with the activator threshold model, classically it has been distinguished between high and low threshold target genes in order to explain how cells receiving the same signal can activate different genes. However, in particular cases where the transcription is controlled by two opposing transcription factors, it has been tested that this logic is not valid. This motivates the necessity for describing new theoretical models in order to understand better these cellular responses. By a theoretical analysis we have deduced different versions of transcriptional logic that are significantly determined by how the opposing transcription factors cooperate between them in the transcription process. We have also tested these different scenarios focussing on the Drosophila Hh target genes, and we have reproduced similar conclusions to the ones obtained by other methodologies.

systems biology↗