Roles for insulin and ecdysteroids in differentiation of an insect cell line of epidermal origin

Summary During postembryonic development of insects, molting cycles affect epidermal cells with alternate periods of proliferation and differentiation. Cells of the cell line established from imaginal discs of the Indian meal moth (IAL-PID2) differentiate under the action of the molting hormone, 20-hydroxyecdysone, in a manner that is meaningful in terms of the development of the tissue from which they were derived. In particular, the hormone caused an accumulation of the cells in the G2 phase of their cycle and induced the formation of epithelial-like aggregates and the synthesis of specific proteoglycans. Recent discovery of members of the insulin superfamily in insects and the role of growth factors played by this family of molecules in vertebrates led us to check for their potential effects on IAL-PID2 cell cycle regulation. On the one hand, our results showed that insulin was involved in partial resumption of the cell cycle after an arrest caused by serum deprivation, but that other growth factors present in fetal calf serum were needed for full completion of mitosis. On the other hand, the cytostatic effect of 20-hydroxyecdysone was reversible, and, prior exposure of the cells to the hormone allowed the cells to complete one cell cycle in serum-free medium. These results suggest that the production of autocrine growth factors induced by ecdysteroids could circumvent the absence of serum. This cell culture model provides potential for further study of interactions between ecdysteroids and growth factor homologs during differentiation of insect epidermal cells.     

Prospects for using genetic transformation for improved SIT and new biocontrol methods

The genetic manipulation of non-drosophilid insect species is possible by the creation of recombinant DNA constructs that can be integrated into host genomes by several transposon-based vector systems. This technology will allow the development and testing of a variety of systems that can improve existing biological control methods, and the development of new highly efficient methods. For programs such as sterile insect technique (SIT), transgenic strains may include fluorescent protein marker genes for detection of released insects, and conditional gene expression systems that will result in male sterility and female lethality for genetic sexing. Conditional expression systems include the yeast GAL4 system and the bacterial Tet-off and Tet-on systems that can, respectively, negatively or positively regulate expression of genes for lethality or sterility depending on a dietary source of tetracycline. Importantly, strains for male sterility must also incorporate an effective system for genetic sexing, since typically, surviving females would remain fertile. Models for the use of these expression systems and associated genetic material come from studies in Drosophila and, while many of these systems should be transferable to other insects, continued research will be necessary in insects of interest to clone genes, optimize germ-line transformation, and perform vector stability studies and risk assessment for their release as transgenic strains.     

Cotton Biotechnology

Genetically modified (GM) cotton altered for insect and herbicide resistance released into commercial production in 1996 to 1997 now accounts for the lion's share of cotton acreage in the U.S. The rapid increase in transgenic cotton acreage in such a short period of time attests to the overall success of agricultural biotechnology. Grower satisfaction with transgenic cotton is largely due to several significant benefits, such as lower production costs, streamlined yet flexible management, and a reduced impact on the environment. This review article provides an overview of what has been accomplished thus far, as well as what improved germplasm may lurk on the horizon. A critical assessment of the gene delivery systems in cotton and possible targets for improvement is presented. The performance of the first generation of transgenic cotton plants engineered for insect, disease, or herbicide resistance is evaluated from the perspective of the benefits, the limitations that impact field performance, and management strategies. A few traits that hold future promise for increasing fiber productivity, enhancing and/or increasing the novelty of cotton-based products for the consumer, and improving human health and well-being are presented. Above all, cotton biotechnology offers to greatly enhance breeding programs by introducing novel traits that have eluded more traditional plant improvement methods and therefore will likely play an increasingly important role in the genetic improvement of cotton.     

Excitable properties of insect neurones in culture: A developmental study

The passive and excitable electrical properties of cockroach neurones growing in vitro have been investigated using intracellular recording techniques. The resting membrane potentials of the neurones are similar to those of their in vivo counterparts but the input resistances and membrane capacitive properties are more typical of embryonic insect neurones. During the first 12 days of growth in vitro the neurones exhibit delayed rectification in response to the injection of depolarising current steps. After this period “all or none” action potentials can be evoked by depolarising pulses in approximately half of the neurones tested. These spikes are abolised by 1 μM tetrodotoxin but are unaffected by 5 mM Co²⁺. Spontaneous excitatory activity develops in approx 25% of the neurones after 3 weeks in culture.     

Modelling Spatio-Temporal Effects of Environment on Atlantic Herring, <Emphasis Type="Italic">Clupea harengus</Emphasis>

Trends in mean abundance of North Sea Atlantic herring, Clupea harengus, over the period of 1992–1995, were modelled as a function of spatial location and ocean environmental conditions using generalized additive models (GAM). In all four years, the average herring abundance was found to be highest in latitudes around 60.5°N, and decreased with increasing latitude. The thermocline depth had a significant effect on prespawning herring abundance both directly, as a main effect, and indirectly, through its interactive effect with the temperature at 60m. Average herring abundance was highest in areas having deeper thermocline depths (up to 45m) and temperatures at 60m between 9 and 11°C. Prespawning herring abundance was greater in areas of cooler surface waters in the south than in the north. Well-mixed waters and transition zones between frontal and stratified areas having sea surface temperatures mainly between 11 and 12°C and to a lesser extent between 13 and 14°C were associated with the highest herring abundance. Herring appeared to avoid the cold bottom waters in summer. Multiyear GAM analysis revealed consistent environmental preferenda of herring and affirmed further a significant decrease in herring abundance. As herring numbers declined, the population aggregated in the most preferred areas. The inter-relationships of herring and environmental factors across the study period, were similar in their structure and significance, suggesting that preferred areas for location of herring can be reasonably predicted.     

Early responses of bark and wood boring beetles to an outbreak of the hemlock looper Lambdina fiscellaria (Guenée) (Lepidoptera: Geometridae) in a boreal balsam fir forest of North America

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Knockdown of Na,K-ATPase β-subunits in Oncopeltus fasciatus induces molting problems and alterations in tracheal morphology

The ubiquitously expressed transmembrane enzyme Na,K-ATPase (NKA) is vital in maintaining functionality of cells. The association of α- and β-subunits is believed to be essential for forming a functional enzyme. In the large milkweed bug Oncopeltus fasciatus four α1-paralogs and four β-subunits exist that can associate into NKA complexes. This diversity raises the question of possible tissue-specific distribution and function. While the α1-subunits are known to modulate cardenolide-resistance and ion-transport efficiency, the functional importance of the β-subunits needed further investigation. We here characterize all four different β-subunits at the cellular, tissue, and whole organismal scales. A knockdown of different β-subunits heavily interferes with molting success resulting in strongly hampered phenotypes. The failure of ecdysis might be related to disrupted septate junction (SJ) formation, also reflected in β2-suppression-induced alteration in tracheal morphology. Our data further suggest the existence of isolated β-subunits forming homomeric or β-heteromeric complexes. This possible standalone and structure-specific distribution of the β-subunits predicts further, yet unknown pump-independent functions. The different effects caused by β knockdowns highlight the importance of the various β-subunits to fulfill tissue-specific requirements.     

REPLY TO “COMMENT ON MARDEN (2013) REGARDING THE INTERPRETATION OF THE EARLIEST TRACE FOSSIL OF A WINGED INSECT”

Benner, Knecht, and Engel have replied to my critique of their interpretation of a Carboniferous trace fossil produced by an insect at the edge of water. Here I respond by pointing out that their reiterated scenario still requires mutually exclusive paths of motion and I show that their assertions of methodological shortcomings are tangential and lack merit. Overall, this discussion provides an opportunity to examine in greater detail competing hypothesis about behaviors and taxonomic identity of the trace maker, and relevance thereof to competing theories regarding early events in the evolution of pterygote insects.