Studying Apoptosis in Drosophila

Comparison of Transcriptome Responses between Sogatella furcifera Females That Acquired Southern Rice Black-Streaked Dwarf Virus and Not

Simple Summary

The southern rice black-streaked dwarf virus (SRBSDV) is transmitted horizontally by the planthopper, Sogatella furcifera. During feeding on virus-infected plants, S. furcifera may acquire or fail to acquire SRBSDV. In this study, the responses were compared among the S. furcifera successfully acquiring the virus, those failing to acquire the virus, and those not exposed to SRBSDV (the control). A total of 1043 and 2932 differentially expressed genes (DEGs) were obtained in S. furcifera females that acquired SRBSDV and that failed to, in comparison with the control, respectively. Functionally, these DEGs are primarily involved in diverse signaling pathways related to primary metabolism and innate immunity, such as apoptosis. Additional bioassays confirmed the activation of apoptosis in S. furcifera by SRBSDV exposure. Interestingly, we also found that six female-specific genes were also upregulated in S. furcifera females exposed to SRBSDV. Our results further the understanding of the interactions between the vector S. furcifera females and SRBSDV at the molecular level.

Abstract

The southern rice black-streaked dwarf virus (SRBSDV) is transmitted horizontally by Sogatella furcifera in a persistent, propagative manner. Exposure of S. furcifera females to SRBSDV-infected rice plants may trigger transcriptomic changes in the insects, the transcriptomes of females that acquired SRBSDV and those that failed to, as well as females fed on healthy rice plants as control, were sequenced and compared. Nine transcriptomic libraries were constructed, from which a total of 53,084 genes were assembled. Among the genes, 1043 and 2932 were differentially expressed genes (DEGs) in S. furcifera females that acquired SRBSDV and that failed to, in comparison with the control, respectively. Functional enrichment analysis showed that DEGs identified in S. furcifera females exposed to SRBSDV are primarily involved in diverse signaling pathways related to primary metabolism and innate immunity. The DEGs in the S. furcifera females that failed to acquire the virus significantly outnumbered that in the insects that acquired the virus, and the virus exposure activated the humoral and cellular immune responses of the vectors, especially the apoptosis. The key gene in apoptosis encoding caspase 1 was upregulated by SRBSDV exposure, especially in S. furcifera females that failed to acquire the virus. Analysis of caspase 1 activity validated that SRBSDV exposure induced caspase 1 accumulation. Surprisingly, the expression of six female-specific genes was also upregulated by SRBSDV exposure, which was confirmed by RT-qPCR analysis. This study provides evidence to explain the differential virus acquisition at the transcriptome level.

Comparative transcriptome analyses of the Drosophila pupal eye

Tissue function is dependent on correct cellular organization and behavior. As a result, the identification and study of genes that contribute to tissue morphogenesis is of paramount importance to the fields of cell and developmental biology. Many of the genes required for tissue patterning and organization are highly conserved between phyla. This has led to the emergence of several model organisms and developmental systems that are used to study tissue morphogenesis. One such model is the Drosophila melanogaster pupal eye that has a highly stereotyped arrangement of cells. In addition, the pupal eye is postmitotic that allows for the study of tissue morphogenesis independent from any effects of proliferation. While the changes in cell morphology and organization that occur throughout pupal eye development are well documented, less is known about the corresponding transcriptional changes that choreograph these processes. To identify these transcriptional changes, we dissected wild-type Canton S pupal eyes and performed RNA-sequencing. Our analyses identified differential expression of many loci that are documented regulators of pupal eye morphogenesis and contribute to multiple biological processes including signaling, axon projection, adhesion, and cell survival. We also identified differential expression of genes not previously implicated in pupal eye morphogenesis such as components of the Toll pathway, several non-classical cadherins, and components of the muscle sarcomere, which could suggest these loci function as novel patterning factors.

Mask, a component of the Hippo pathway, is required for Drosophila eye morphogenesis

Hippo signaling is an important regulator of tissue size, but it also has a lesser-known role in tissue morphogenesis. Here we use the Drosophila pupal eye to explore the role of the Hippo effector Yki and its cofactor Mask in morphogenesis. We found that Mask is required for the correct distribution and accumulation of adherens junctions and appropriate organization of the cytoskeleton. Accordingly, disrupting mask expression led to severe mis-patterning and similar defects were observed when yki was reduced or in response to ectopic wts. Further, the patterning defects generated by reducing mask expression were modified by Hippo pathway activity. RNA-sequencing revealed a requirement for Mask for appropriate expression of numerous genes during eye morphogenesis. These included genes implicated in cell adhesion and cytoskeletal organization, a comprehensive set of genes that promote cell survival, and numerous signal transduction genes. To validate our transcriptome analyses, we then considered two loci that were modified by Mask activity: FER and Vinc, which have established roles in regulating adhesion. Modulating the expression of either locus modified mask mis-patterning and adhesion phenotypes. Further, expression of FER and Vinc was modified by Yki. It is well-established that the Hippo pathway is responsive to changes in cell adhesion and the cytoskeleton, but our data indicate that Hippo signaling also regulates these structures.

Cell Biology During Infection of Plant Viruses in Insect Vectors and Plant Hosts

Plant viruses typically cause severe pathogenicity in plants, even resulting in the death of plants. Many pathogenic plant viruses are transmitted in a persistent manner via insect vectors. Interestingly, unlike in the plant hosts, persistent viruses are either nonpathogenic or show limited pathogenicity in their insect vectors, while taking advantage of the cellular machinery of insect vectors for completing their life cycles. This review discusses why persistent plant viruses are nonpathogenic or have limited pathogenicity to their insect vectors while being pathogenic to plants hosts. Current advances in cell biology of virus-insect vector interactions are summarized, including virus-induced inclusion bodies, changes of insect cellular ultrastructure, and immune response of insects to the viruses, especially autophagy and apoptosis. The corresponding findings of virus-plant interactions are compared. An integrated view of the balance strategy achieved by the interaction between viral attack and the immune response of insect is presented. Finally, we outline progress gaps between virus-insect and virus-plant interactions, thus highlighting the contributions of cultured cells to the cell biology of virus-insect interactions. Furthermore, future prospects of studying the cell biology of virus-vector interactions are presented.

Fibrillar structures induced by a plant reovirus target mitochondria to activate typical apoptotic response and promote viral infection in insect vectors

Numerous plant viruses that cause significant agricultural problems are persistently transmitted by insect vectors. We wanted to see if apoptosis was involved in viral infection process in the vector. We found that a plant reovirus (rice gall dwarf virus, RGDV) induced typical apoptotic response during viral replication in the leafhopper vector and cultured vector cells, as demonstrated by mitochondrial degeneration and membrane potential decrease. Fibrillar structures formed by nonstructural protein Pns11 of RGDV targeted the outer membrane of mitochondria, likely by interaction with an apoptosis-related mitochondrial protein in virus-infected leafhopper cells or nonvector insect cells. Such association of virus-induced fibrillar structures with mitochondria clearly led to mitochondrial degeneration and membrane potential decrease, suggesting that RGDV Pns11 was the inducer of apoptotic response in insect vectors. A caspase inhibitor treatment and knockdown of caspase gene expression using RNA interference each reduced apoptosis and viral accumulation, while the knockdown of gene expression for the inhibitor of apoptosis protein improved apoptosis and viral accumulation. Thus, RGDV exploited caspase-dependent apoptotic response to promote viral infection in insect vectors. For the first time, we directly confirmed that a nonstructural protein encoded by a persistent plant virus can induce the typical apoptotic response to benefit viral transmission by insect vectors.

Drosophila melanogaster "a potential model organism" for identification of pharmacological properties of plants/plant-derived components

Plants/plant-derived components have been used from ancient times to treat/cure several human diseases. Plants and their parts possess several chemical components that play the vital role in the improvement of human health and their life expectancy. Allopathic medicines have been playing a key role in the treatment of several diseases. Though allopathic medicines provide fast relief, long time consumption cause serious health concerns such as hyperallergic reactions, liver damage, etc. So, the study of medicinal plants which rarely cause any side effect is very important to mankind. Plants contain many health benefit properties like antioxidant, anti-aging, neuroprotective, anti-genotoxic, anti-mutagenic and bioinsecticidal activity. Thus, identification of pharmacological properties of plants/plant-derived components are of utmost importance to be explored. Several model organisms have been used to identify the pharmacological properties of the different plants or active components therein and Drosophila is one of them. Drosophila melanogaster "fruit fly" is a well understood, high-throughput model organism being used more than 110 years to study the different biological aspects related to the development and diseases. Most of the developmental and cell signaling pathways and ∼75% human disease-related genes are conserved between human and Drosophila. Using Drosophila, one can easily analyze the pharmacological properties of plants/plant-derived components by performing several assays available with flies such as survivorship, locomotor, antioxidant, cell death, etc. The current review focuses on the potential of Drosophila melanogaster for the identification of medicinal/pharmacological properties associated with plants/plant-derived components.

In the Midst of Life-Cell Death: What Is It, What Is It Good for, and How to Study It

Cell death, one of the most fundamental biological processes, has not made it into the public consciousness in the same way that genetic inheritance, cell division, or DNA replication has. Everyone knows they get their genes from their parents, but few would be aware that even before they were born a lot of essential cell death has shaped their development. The greater population, for the most part, is blissfully unaware that every day millions of their own cells die in a programmed way and that this is essential for normal human physiology-their well-being, in fact. Nowhere is the burial liturgy, "In the midst of life we are in death," more apt. Despite this public underappreciation, cell death research is a major industry. A search in PubMed for "apoptosis," a special form of cell death that is caused by caspases, returns approximately 280,000 hits. The intense research interest arises from the realization that abnormal cell death responses play an important role in two of the biggest killers in the western world: cancer and cardio/cerebrovascular disease. Furthermore, the manner in which cells die can also influence the development of autoimmune and autoinflammatory diseases. It is therefore of paramount importance to ensure that experiments accurately quantitate and correctly identify cell death in all its guises. That is the goal of this protocol collection.

CasExpress reveals widespread and diverse patterns of cell survival of caspase-3 activation during development in vivo

Caspase-3 carries out the executioner phase of apoptosis, however under special circumstances, cells can survive its activity. To document systematically where and when cells survive caspase-3 activation in vivo, we designed a system, CasExpress, which drives fluorescent protein expression, transiently or permanently, in cells that survive caspase-3 activation in Drosophila. We discovered widespread survival of caspase-3 activity. Distinct spatial and temporal patterns emerged in different tissues. Some cells activated caspase-3 during their normal development in every cell and in every animal without evidence of apoptosis. In other tissues, such as the brain, expression was sporadic both temporally and spatially and overlapped with periods of apoptosis. In adults, reporter expression was evident in a large fraction of cells in most tissues of every animal; however the precise patterns varied. Inhibition of caspase activity in wing discs reduced wing size demonstrating functional significance. The implications of these patterns are discussed.

DOI:http://dx.doi.org/10.7554/eLife.10936.001

Every day, individual cells in our body actively decide whether to live or die. There are enzymes called executioner caspases that help cells to die in a carefully controlled process called apoptosis. Although the activation of executioner caspases generally leads to apoptosis, there are some circumstances in which cells are able to survive.

Fruit flies are often used in research as models of how animals grow and develop. Ding, Sun et al. set out to find out more about the circumstances in which cells manage to survive caspase activation in fruit flies. The experiments used a new method that results in cells that survive caspase activity producing a fluorescent marker protein. This allowed Ding, Sun et al. to track when and where these events occurred in the flies.

Few cells in fruit fly embryos survive the activation of executioner caspase. However, in later stages of development, more and more cells survive this process. Cells in different parts of the body responded differently. For some types of cells, every cell seemed to survive caspase activity with no evidence of apoptosis. In other tissues like the central brain, in which a few cells normally choose to die, some cells occasionally managed to survive the activation of caspases. This rescue from the brink of death was more common than Ding, Sun et al. had anticipated.

The next step will be to uncover the molecular mechanisms that enable the cells to survive caspase activity. This knowledge may help us to develop treatments that can promote the survival of useful cells like heart muscle cells and brain cells, or trigger the death of cancer cells.

DOI:http://dx.doi.org/10.7554/eLife.10936.002