Lipid metabolism

Lipids have a wide range of crucial roles for insects such as meeting the energy needs for insect growth and development, starvation and diapause, flight and migration; as well as the nutrition of the embryo in reproductive physiology. The fat body is the coordination center of insect lipid metabolism and orthologous to mammalian liver, white adipose tissue and immune system. The Fat body stores the lipid necessary for long term energy supply during the winter when insects do not feed. This period is considered as ‘diapause’, a stage when insects enter into a static state to over-winter or survive adverse conditions. In this regard, we focus on several different models that have mandatory or facultative hibernation. The former one include the sunnpest, Eurygaster maura and the wheat stink bug, Aelia rostra; while the latter include the Colorado potato beetle. We use transcriptomics, proteomics and functional genomics to detect the primary actors of lipid metabolism and their particular roles.

Another particular interest in our group is the interaction between lipid metabolism and calicum homeostasis.  The endoplasmic reticulum is a key cellular organelle coordinating lipid biosynthesis.  ER is also the main site of Ca2+ storage in the cell. Ca2+ in the ER is essential for chaperone-mediated protein folding and secretion, as well as for the function of metabolic enzymes. Our focus under this topic is the basic genes of calcium homestasis such as SERCA, which pumps Ca2+ from the cytosol into the ER lumen, and the IP3 receptor (IP3R), which release Ca2+ from the ER into the cytosol. In addition to SERCA and IP3Rs, we are also examining the role of the STIM-Orai complex in insect lipid metabolism.

Our data indicate that insect fat body and lipid metabolism could be good targets in the development of new pest control strategies. Additionally,  our data is promising in understanding the human lipid metabolism disorders such as Non-alcoholic fatty liver disease (NAFLD) thus,, insects and mammalians share many common genetic actors and pathways in lipid metabolism .

Peritrophic matrix

The vertebrate mucosal layer is an essential feature of the digestive tract and lubricates the passage of food along, as well as protects it from digestive enzymes. The insect midgut contains the peritrophic matrix, the tissue that is orthologous in both structure and function to the mucosal layer. The peritrophic matrix is an essential organ of the insect digestive physiology as it protects the midgut epithelium from abrasion by rough food particles and proteolysis by digestive enzymes, as well as from infection by pathogens, and damage by xenobiotics such as plant allelochemicals or insecticides. Important functions of the peritrophic matrix and its accessibility via feeding make it particularly a good target site for pest control strategies.

The peritrophic matrix is composed of chitin and proteins. The chitin in the peritrophic matrix is synthesized by the midgut specific chitin synthase, modified by enzymes such as chitin deacetylase, and degraded by chitinases during molting. Structural peritrophic matrix proteins, called peritrophins, interact with the chitin scaffold and contribute structural and functional features to the peritrophic matrix such as integrity, elasticity and permeability. We have been working on the molecular architecture and functions of the peritrophic matrix in the cotton leafworm Spodoptera littoralis (Lepidoptera:Noctuidae) and Leptinotarsa decemlineata. We completed dectection of the entire protein suit of the peritrophic matrices in both species and our data suggest that the biochemical composition of the PM in lepidopterans and coleopterans differ.  Our current work focus on the function of select proteins using CRISPR/Cas9 system in S. littoralis and the RNAi in L.decemlineata. Our data is promising in terms of development of new target sites in pest control.

Insect Immunity & Defense against entomopathogens

Cellular and humoral responses are important in inhibiting the systemic infections by pathogens. Cellular responses include phagocytosis, encapsulation and nodule formation, while humoral immunity includes primarily the secretion of antimicrobial peptides (AMPs) such as defensin, cecropin-1 and -2, gambicins. Cellular responses are mediated by plasmatocytes and granulocytes, while AMPs are produced by fat body and hemocytes; as well as the midgut and a cluster of cells at the foregut/midgut junction, known as proventriculus (cardia). AMPs have been shown to be induced upon microbial challange in many insects. We have been working on humoral immunity in several different models such as the Leptinotarsa decemlieneta, and two major pests of grain in Turkey, the Wheat stinkbug and the sunnpest (Eurygaster maura). We identified various novel AMPs in these pests using proteom, transcriptome and RNAi analyses from the fat body and midgut upon microbial challange by various pathogens such as Bacillus thuringiensis.

The insect peritrophic matrix and vertebrate mucusal layer share also defensive proteins such as mucins. Our studies revealed presence of different types of insect intestinal mucins based on their structural domain organizations in the lepidopteran models. A type denoted “complex mucins” associated with the bertha armyworm peritrophic matrix are targeted during baculovirus infection by a metalloprotease encoded by the viral genome, while the “binary type mucins” are not. Such findings had great potential in terms of development of more effective baculoviruses via recombination technology. Indeed, our collaborators in Canada (Drs. Dwayne Hegedus, Martin Erlandson and David Theilmann) developed a recombinant baculovirus encoding the baculoviral metalloprotease and found that it was almost 4.5 times more effective than the wild strain baculovirus. We currently work on development of a new baculovirus formulation targeting the mucin functioning via chemical reagents. This formulation technology was already tested both in the laboratory and was found to significantly improve baculovirus efficacy up to 30-40%. Fundamentally, it could be applied to other lepidopteran hosts, as it targets the essential features of the common defense components of the lepidopteran peritrophic matrix. In particular, understanding the resistance mechanism of binary type mucins against metalloproteases is a current interest for us right now.

Circadian clock

Throughout the evolution’s convoluted steps; every organism that is sensitive to light must have acquired endogenously ticking clocks in order to exploit the good conditions of the day at the right times by anticipating them beforehand. Without a doubt, insects are among those many organisms that utilize their circadian clocks to ensure their survival. Many insects have another great weapon in their arsenal which renders them resistant towards adverse environmental conditions such as lack of daylight, detrimental temperatures and lack of adequate food. That particular state is called diapause. There are many cues, token stimuli, which can trigger the switch from the development pathway to the diapause pathway. These cues comprise inputs such as photoperiod, thermoperiod or food quantity. Although there are ample amount of cues out in nature, photoperiod is often the most crucial one. Leptinotarsa decemlineata which is a major pest of plants in the Solanaceae family exhibits robust photosensitivity while choosing the time of the diapause onset. There are many theories out there that tried to link the diapause behavior and circadian clocks. In this regards, establishments of circadian genes’ patterns in a beetle system is very promising as the insect shows a robust photosensitivity and unambiguous diapause behavior in order to overcome the tough winters under the soil.