1,721,038 research outputs found
Genetic control of the diamondback moth (Plutella xylostella L.)
Full text linkInsect pests represent major threats to food production, biodiversity conservation, and human and animal health. Currently, the most widespread strategy to control their populations is through the spraying of synthetic chemical insecticides. However, the overuse of these compounds has had significant negative environmental consequences. Additionally, our reliance on insecticides has resulted in major reductions in their efficacy through pest-evolved resistance. To successfully manage insect pests, while avoiding environmental degradation, thus requires the development of novel, more sustainable, pest management strategies. Recent advances in our understanding of recombinant DNA methods and molecular biology have allowed the application of transgenic tools to pest management. Here, synthetic genes can be engineered, transformed into the genomes of pest species, and transported into wild target populations through the natural mating behaviour of the insect. A strategy in which these transgenes are lethal to those insects inheriting them in the field is known as RIDL – Release of Insects carrying a Dominant Lethal. A variant of RIDL limits this lethality to females – female specific RIDL (fsRIDL) – which explicitly targets the reproductive capacity of a target population. The aim of this thesis is to investigate the application of such an fsRIDL strategy to the diamondback moth (Plutella xylostella L.). This economically important pest of brassica crops is highly adept at developing resistance to insecticides and is considered extremely difficult to manage effectively. I present findings which demonstrate the power of diamondback moth lines transformed with fsRIDL transgenes to eliminate target pest populations, and combine synergistically with other transgenic control strategies such as Bt crops in counteracting the evolution of pesticide resistance. Additionally, an exploration into an alternative gene expression system to that used in current RIDL strategies – the Q system – suggests that not all expression systems will be suitable for transgene control within this highly specific framework. It is hoped that this work will contribute towards the effective control of the diamondback moth, and form a model for the sustainable control of other lepidopteran species through genetic pest management
Recommended from our members
Protochordate Zic genes define primitive somite compartments and highlight molecular changes underlying neural crest evolution
No full textThe vertebrate Zic gene family encodes C2H2 zinc finger transcription factors closely related to the Gli proteins. Zic genes are expressed in multiple areas of developing vertebrate embryos, including the dorsal neural tube where they act as potent neural crest inducers. Here we describe the characterization of a Zic ortholog from the amphioxus Branchiostoma floridae and further describe the expression of a Zic ortholog from the ascidian Ciona intestinalis. Molecular phylogenetic analysis and sequence comparisons suggest the gene duplications that formed the vertebrate Zic family were specific to the vertebrate lineage. In Ciona maternal CiZic/Ci-macho1 transcripts are localized during cleavage stages by asymmetric cell division, whereas zygotic expression by neural plate cells commences during neurulation. The amphioxus Zic ortholog AmphiZic is expressed in dorsal mesoderm and ectoderm during gastrulation, before being eliminated first from midline cells and then from all neurectoderm during neurulation. After neurulation, expression is reactivated in the dorsal neural tube and dorsolateral somite. Comparison of CiZic and AmphiZic expression with vertebrate Zic expression leads to two main conclusions. First, Zic expression allows us to define homologous compartments between vertebrate and amphioxus somites, showing primitive subdivision of vertebrate segmented mesoderm. Second, we show that neural Zic expression is a chordate synapomorphy, whereas the precise pattern of neural expression has evolved differently on the different chordate lineages. Based on these observations we suggest that a change in Zic regulation, specifically the evolution of a dorsal neural expression domain in vertebrate neurulae, was an important step in the evolution of the neural crest
Developmental signature, synaptic connectivity and neurotransmission are conserved between vertebrate hair cells and tunicate coronal cells
No full textIn tunicates, the coronal organ represents a sentinel checking particle entrance into the pharynx. The organ differentiates from an anterior embryonic area considered a proto-placode. For their embryonic origin, morphological features and function, coronal sensory cells have been hypothesized to be homologues to vertebrate hair cells. However, vertebrate hair cells derive from a posterior placode. This contradicts one of the principle historical criteria for homology, similarity of position, which could be taken as evidence against coronal cells/hair cells homology. In the tunicates Ciona intestinalis and C. robusta, we found that the coronal organ expresses genes (Atoh, Notch, Delta-like, Hairy-b, and Musashi) characterizing vertebrate neural and hair cell development. Moreover, coronal cells exhibit a complex synaptic connectivity pattern, and express neurotransmitters (Glu, ACh, GABA, 5-HT, and catecholamines), or enzymes for their synthetic machinery, involved in hair cell activity. Lastly, coronal cells express the Trpa gene, which encodes an ion channel expressed in hair cells. These data lead us to hypothesize a model in which competence to make secondary mechanoreceptors was initially broadly distributed through placode territories, but has become confined to different placodes during the evolution of the vertebrate and tunicate lineages
A Notch-regulated proliferative stem cell zone in the developing spinal cord is an ancestral vertebrate trait
No full textThe genetics of cranial sensory ganglia development and evolution
Full text linkVertebrates perceive the world through sensory neurons of their cranial nerves that connect primary sensory receptors to the brain. The bodies of these neurons are organized in cranial sensory ganglia (CSG) in the head. CSG are considered a vertebrate novelty and they develop from neurogenic placodes and neural crest. The genetic network underlying their early development has been relatively well studied and placodal cell homologs have been suggested in other chordates. However, knowledge has been lacking on the evolution of different ganglia and their neurons. Undertaking a comparative approach, cyclostomes and tunicates are used here to look into the molecular identity and evolution of CSG sensory cells. First, conserved pan-vertebrate markers of the ganglia are identified by exploring the expression and specificity of candidate genes in lamprey embryos. Two of these marker gene families are the starting ground for a comparative investigation of sensory cell types between vertebrates and other chordates. Conserved expression and regulation of the estrogen related receptor (ERR) between lamprey and gnathostomes is presented. It is revealed that a single ERR homolog acquired a role in the development of the vestibuloacoustic ganglion in early vertebrates. Invertebrate sensory expression highlights ERR as an ancient sensory cell marker in bilaterian animals, suggesting a mode of evolution at cell type level. The Hmx homeobox gene family is then identified to ubiquitously mark all CSG and possess conserved genomic architecture across vertebrates. A unique enhancer pair is reported, derived by tandem duplication, connected to ancestral regulation of expression in the central and peripheral nervous systems. Hmx expression and function in Ciona embryos, combined with vertebrate data, provide evidence of homology between CSG and tunicate sensory neurons. Finally, a review is carried out, discussing how placodal and CSG components gradually evolved and assembled under new genomic organization and control in vertebrates
Lamprey neural Helix-Loop-Helix (HLH) genes and the evolution of the vertebrate nervous system
Full text linkTranscription factors of the helix-loop-helix (HLH) gene family are widespread in the animal kingdom. Among them, members of HLH subfamilies such as ASCL, Neurogenin, NeuroD, COE, Atonal, Oligo, NSCL, Hairy/E(spl) and Hey (here referred to as neural HLH genes) have been shown to be fundamental for the development of the nervous system. They are expressed at different time periods of neuronal differentiation, from the specification of ectoderm towards a neural lineage, to the ultimate differentiation of neurons. Few HLH genes have been identified in the lamprey; however, considering the wide diversity of HLH gene subfamilies in metazoans, including vertebrates, it is very likely that lampreys possess a large repertoire of HLH genes in their genome. In the present study, the identification of several HLH genes in the lamprey genome, as well as the isolation and expression of different lamprey neural HLH genes is reported. As expected, a wide repertoire of HLH genes was identified in the sea lamprey (Petromyzon marinus) genome. On the other hand, the identification and expression analysis of different neural HLH genes of the ASCL, Neurogenin, COE and Hairy/E(spl) in the brook lamprey Lampetra planeri showed an overall conservation with other vertebrates, both at the sequence and expression pattern levels. In addition, novel features of the lamprey nervous system are revealed, such as the identification of possible new sensory cranial placodes in pharyngeal arches. Furthermore, these genes can serve as molecular markers for different cranial placodes and dorsal root ganglia (DRG), and their expression also highlights the presence of a ventricular zone in the brain and spinal cord, along with a complementary marginal zone. Finally, with the use of a Notch pathway inhibitor in developing L. planeri embryos, the regulation of expression of the isolated genes by the Notch signaling pathway was shown to be generally conserved between lampreys and gnathostomes in the spinal cord. This functional study also revealed that the lamprey spinal cord likely presents an independent developmental programme from the brain. All together, the present study shows that the analysis of neural HLH genes represents an excellent tool to understand the lamprey nervous system
Asymmetry in spiralian development
Full text linkIn animal development, how an animal builds its body has been a fundamental and central question. Spanning different fields, we have a good understanding of how animals build their body axes (anterior-posterior, dorsal-ventral) and this understanding is now a routine concept when learning about animal development. There are a number of mysteries left when considering early development, and the establishment of left-right (LR) asymmetry remains one of them. One key problem is how initial symmetry is broken early in animal development and how this translates into molecular asymmetry. Our lack of understanding is based on the difficulty of adapting available techniques to non-model species. This thesis uses an alternative approach to the current LR asymmetry models, and reveals that by adapting techniques to non-model organisms and by using newly available technologies, there is still much to be learned and discovered in embryology
Why do whales exist? cancer resistance in cetaceans
Full text linkCancer is the inevitable fate for all multicellular organisms should they live long enough. However, if all mammalian cells have approximately equivalent probabilities of cancer-associated gene mutation then, all else being equal, the number of cells susceptible to transformation should scale with body size and longevity, implying larger, longer-lived mammals such as whales should be disproportionately more prone to cancer than smaller mammals, such as mice, simply due to cell number alone. Empirical evidence to date does not support this prediction, and the discrepancy between theory and observation is known as Peto’s paradox.
The mere existence of whales and other large mammals demands the evolution of a suite of cancer suppressive mechanisms in order to resolve the paradox; the establishment and understanding of which being the focus of this research.
First, cancer incidence rates across the animal kingdom are collected and assessed, quantitatively revealing the veracity of Peto’s paradox and the relationship between incidence risk and scaling basal metabolic rate. Next, computational models are developed to test the hypothesis that intrinsic metabolic scaling may itself be sufficient to explain Peto’s paradox. Results reveal that though incorporating scaling life-history traits into the narrative helps, they alone aren’t sufficient to explain cancer suppression in large mammals. Instead, genetic control is established as playing a crucial role. Finally, comparative analysis of the available cetacean genomes and transcriptomes uncovers several gene duplication events in key cancer-associated pathways, alongside lineage-specific and
size-dependent selection in gene families associated with cancer resistance. This work demonstrates though there exists no singular explanation for Peto’s paradox, the disparate mechanisms that underlie the trajectory towards cancer resistance in independent lineages are all variations on a theme - the understanding of which may elucidate insight towards the development of future targets for human cancer therapies
Evolution and development of the olfactory neurons in the olfactores clade
Full text linkIn vertebrates, specialised olfactory systems and associated neurons are crucial to sense the outside chemical world. They also play a notable part in reproduction with the role of GnRH-producing neurons, derived from the olfactory placode, in sexual maturation and fertility. Despite the vital importance of these olfactory cell types, our knowledge of their evolutionary origin remains limited. In this work, a comparative approach is undertaken to study the development of olfactory neurons and provide insights into their evolutionary history. Two main organisms are used for comparison: the lamprey Lampetra planeri and the ascidian Ciona intestinalis. These model species are used to investigate the expression, regulation, and function of specific genes to trace olfactory cell type relationships across vertebrates and their chordate relatives. First, the embryonic origin and specification of hypothalamic GnRH secretory neurons in lamprey is examined to develop a pan-vertebrate view of the origin and specification of these crucial neurosecretory cells. The potential association during embryogenesis with the developing olfactory system is investigated and this study provides support for the hypothesis that lamprey hypothalamic GnRH cells do not derive from the nasal placode, despite some specification mechanisms appearing conserved with olfactory-derived GnRH neurons of jawed vertebrates. Second, it is revealed that the palp axial columnar cells (ACCs) of Ciona have homologies with olfactory sensory and secretory neurons of vertebrates. The regulation, expression, and function of MS4A and GnRH genes in the palp ACCs, combined with data from vertebrates, suggest a common evolutionary origin at cell-type level to explain how the olfactory-derived cell types in vertebrates derived from an ACC-like GnRH/chemosensory multifunctional precursor by segregation of functions. Finally, a microfluidic chip for immobilisation and controlled stimulation of Ciona larvae is designed and built to interrogate whether the larva responds to chemical stimuli. The detection by live cell calcium imaging of a CO2-evoked response upon chemical stimulation represents the first experimental evidence that ascidian larva sense chemical cues in their environment and provides a valuable tool for further investigations
- …
