Biology subjects

Yagound, B.

Publications and source records attributed to Yagound, B..

6 recordsLinked to original sources

bioRxiv2023

Is developmental plasticity triggered by DNA methylation changes in the invasive cane toad (Rhinella marina)?

Many organisms can adjust their development according to environmental conditions, including the presence of conspecifics. Although this developmental plasticity is common in amphibians, its underlying molecular mechanisms remain largely unknown. Exposure during development to either cannibal cues from older conspecifics, or alarm cues from injured conspecifics, causes reduced growth and survival in cane toad (Rhinella marina) tadpoles. Epigenetic modifications, such as changes in DNA methylation patterns, are a plausible mechanism underlying these developmental plastic responses. Here we tested this hypothesis, and asked whether cannibal cues and alarm cues trigger the same DNA methylation changes in developing cane toads. We found that exposure to both cannibal cues and alarm cues induced local changes in DNA methylation patterns. These DNA methylation changes affected genes putatively involved in developmental processes, but in different genomic regions for different conspecific-derived cues. Genetic background explained most of the epigenetic variation among individuals. Overall, the molecular mechanisms triggered by exposure to cannibal cues seem to differ from those triggered by alarm cues. Studies linking epigenetic modifications to transcriptional activity are needed to clarify the proximate mechanisms that regulate developmental plasticity in cane toads.

molecular biology↗

bioRxiv2023

Infection by the lungworm Rhabdias pseudosphaerocephala affects the expression of immune-related microRNAs by its co-evolved host, the cane toad Rhinella marina.

Parasites may suppress the immune function of an infected host using microRNAs (miRNAs) to prevent protein production. Nonetheless, little is known about the diversity of miRNAs and their mode(s) of action. In this study, we investigated the effects of infection by a parasitic lungworm (Rhabdias pseudosphaerocephala) on miRNA and mRNA expression of its host, the invasive cane toad (Rhinella marina). We compared miRNA and mRNA expression in naive toads that had never been infected by lungworms to toads that were infected with lungworms for the first time in their lives, and to toads that were infected the second time in their lives (i.e., had two consecutive infections). In total, we identified 434 known miRNAs and 106 potential novel miRNAs. Compared to uninfected toads, infected animals upregulated five (single-infection treatment) or four (multiple-infection treatment) miRNAs. Seven of these differentially expressed miRNAs were associated with gene pathways related to the immune response, potentially reflecting immunosuppression of cane toads by their parasites. Infected hosts did not respond with substantial mRNA transcription, with only one differentially expressed gene between control and single-infection hosts. Our study suggests that miRNA-mediated interactions may play a role in mediating the interaction between the parasite and its host. Our findings clarify the role of miRNAs in host-parasite interactions, in a system in which an ongoing range expansion by the host has generated substantial divergence in host-parasite interactions.

genetics↗

bioRxiv2021

Brain transcriptome analysis reveals gene expression differences associated with dispersal behaviour between range-front and range-core populations of invasive cane toads in Australia

Understanding the mechanisms underlying rapid adaptation of invasive species in novel environments is key to improving our ability to manage these species. Many invaders demonstrate rapid evolution of behavioural traits involved in range expansion such as locomotor activity, exploration and risk-taking. However, the molecular mechanisms that underpin these changes are poorly understood. In 86 years, invasive cane toads (Rhinella marina) in Australia have drastically expanded their geographic range westward from coastal Queensland to Western Australia. During their range expansion, toads have undergone extensive phenotypic changes, particularly in behaviours that enhance the toads dispersal ability. Common-garden experiments have shown that some changes in behavioural traits related to dispersal are heritable. However, genetic diversity is greatly reduced across the invasive range due to a strong founder effect, and the genetic basis underlying dispersal-related behavioural changes remains unknown. Here we used RNA-seq to compare the brain transcriptomes of toads from the Hawaiian source population, as well as three distinct populations from across the Australian invasive range. We found markedly different gene expression profiles between the source population and Australian toads. By contrast, cane toads from across the Australian invasive range had very similar transcriptomic profiles. Yet, key genes with functions putatively related to dispersal behaviour showed differential expression between range-core and range-front populations. These genes could play an important role in the behavioural changes characteristic of range expansion in Australian cane toads.

genomics↗

bioRxiv2021

Abundant small RNAs in the reproductive tissues of the honey bee, Apis mellifera, are a plausible mechanism for epigenetic inheritance and parental manipulation of gene expression

Polyandrous social insects such as the honey bee are prime candidates for parental manipulation of gene expression in offspring. Although there is good evidence for parent-of-origin effects in honey bees the epigenetic mechanisms that underlie these effects remain a mystery. Small RNA molecules such as miRNAs, piRNAs and siRNAs play important roles in transgenerational epigenetic inheritance and in the regulation of gene expression during development. Here we present the first characterisation of small RNAs present in honey bee reproductive tissues: ovaries, spermatheca, semen, fertilised and unfertilised eggs, and testes. We show that semen contains fewer piRNAs relative to eggs and ovaries, and that piRNAs and miRNAs which map antisense to genes involved in DNA regulation and developmental processes are differentially expressed between tissues. tRNA fragments are highly abundant in semen and have a similar profile to those seen in semen in other animals. Intriguingly we find abundant piRNAs that target the sex determination locus, suggesting that piRNAs may play a role in honey bee sex determination. We conclude that small RNAs play a fundamental role in honey bee gametogenesis and reproduction and provide a plausible mechanism for parent-of origin-effects on gene expression and reproductive physiology.

genomics↗

bioRxiv2021

DNA methylation is not a driver of gene expression reprogramming in young honey bee workers

Intragenic DNA methylation, also called gene body methylation, is an evolutionarily-conserved epigenetic mechanism in animals and plants. In social insects, gene body methylation is thought to contribute to behavioral plasticity, for example between foragers and nurse workers, by modulating gene expression. However, recent studies have suggested that the majority of DNA methylation is sequence-specific, and therefore cannot act as a flexible mediator between environmental cues and gene expression. To address this paradox, we examined whole-genome methylation patterns in the brains and ovaries of young honey bee workers that had been subjected to divergent social contexts: the presence or absence of the queen. Although these social contexts are known to bring about extreme changes in behavioral and reproductive traits through differential gene expression, we found no significant differences between the methylomes of workers from queenright and queenless colonies. In contrast, thousands of regions were differentially methylated between colonies, and these differences were not associated with differential gene expression in a subset of genes examined. Methylation patterns were highly similar between brain and ovary tissues and only differed in nine regions. These results strongly indicate that DNA methylation is not a driver of differential gene expression between tissues or behavioral morphs. Finally, despite the lack of difference in methylation patterns, queen presence affected the expression of all four DNA methyltransferase genes, suggesting that these enzymes have roles beyond DNA methylation. Therefore, the functional role of DNA methylation in social insect genomes remains an open question.

genomics↗

bioRxiv2018

Vector-mediated viral transmission favours less virulent viruses

While it is well-established that the ectoparasitic mite Varroa destructor is largely responsible for the widely-reported decline of populations of the Western honeybee Apis mellifera, the exact role the mite plays in honeybee health remains unclear. The last few years have seen a surge in studies associating RNA viruses vectored by the mite with the death of honeybee colonies. Varroa facilitates the spread of RNA viruses because it feeds on developing bee brood and transfers haemolymph from bee-to-bee. Such a change in transmission, from horizontal and vertical to vector-based, is predicted to lead to an increase in virulence of RNA viruses, thus potentially providing an explanation for the observed association between Varroa and certain viruses. Here we document the effect of changing the route of transmission of honeybee viruses contained in the haemolymph of honeybee pupae. We find that a change in mode of transmission rapidly increases viral titres of two honeybee viruses, Sacbrood virus (SBV) and Black queen cell virus (BQCV). This increase in viral titre is accompanied by an increase in virulence. In contrast, the virus most often associated with Varroa, Deformed wing virus (DWV), shows a reduction in viral titre in the presence of SBV and BQCV. In addition, DWV does not cause mortality to honeybee pupae in isolation. Most likely a change in mode of transmission due to the arrival of a vector quickly eliminates the most virulent honeybee viruses resulting in an association between Varroa and less virulent viruses such as DWV. Our work therefore provides empirical evidence for an alternative explanation for the widely-observed association between Varroa and DWV.

evolutionary biology↗