In vivo gene transfer into the adult honeybee brain by using electroporation

In-vivo egfp expression in the honeybee Apis mellifera induced by electroporation and viral expression vector

In this study we describe egfp expression induced by two techniques: in vivo electroporation and viral transduction in several cell types of the adult honeybee brain. Non-neuronal and neuronal cell types were identified and the expression persisted at least during three days. Kenyon cells, optic lobe neurons and protocerebral lobe neurons were electroporated. Astrocyte-like glia cells, fibrous lamellar glia cells and cortex glia cells were identified. Viral transduction targeted one specific type of glia cells that could not be identified. EGFP positive cells types were rather variable after electroporation, and viral transduction resulted in more homogenous groups of positive cells. We propose that these techniques remain a good alternative to transgenic animals because they potentially target only somatic cells.

Genetics in the Honey Bee: Achievements and Prospects toward the Functional Analysis of Molecular and Neural Mechanisms Underlying Social Behaviors

The European honey bee is a model organism for studying social behaviors. Comprehensive analyses focusing on the differential expression profiles of genes between the brains of nurse bees and foragers, or in the mushroom bodies—the brain structure related to learning and memory, and multimodal sensory integration—has identified candidate genes related to honey bee behaviors. Despite accumulating knowledge on the expression profiles of genes related to honey bee behaviors, it remains unclear whether these genes actually regulate social behaviors in the honey bee, in part because of the scarcity of genetic manipulation methods available for application to the honey bee. In this review, we describe the genetic methods applied to studies of the honey bee, ranging from classical forward genetics to recently developed gene modification methods using transposon and CRISPR/Cas9. We then discuss future functional analyses using these genetic methods targeting genes identified by the preceding research. Because no particular genes or neurons unique to social insects have been found yet, further exploration of candidate genes/neurons correlated with sociality through comprehensive analyses of mushroom bodies in the aculeate species can provide intriguing targets for functional analyses, as well as insight into the molecular and neural bases underlying social behaviors.

Efficacy of In Vivo Electroporation on the Delivery of Molecular Agents into Aphid (Hemiptera: Aphididae) Ovarioles

While the wealth of genomic data presently available is increasing rapidly, the advancement of functional genomics technologies for the large majority of these organisms has lagged behind. The Clustered Regularly Interspaced Palindromic Repeats (CRISPR)/Cas9 system is an emerging gene-editing technology derived from a bacterial adaptive immune system that has proven highly effective in multiple model systems. Here, the CRISPR/Cas9 system was delivered into the ovarioles of the pea aphid, Acyrthosiphon pisum (Harris) (Hemiptera, Aphididae), with a new delivery method utilizing in vivo electroporation. To validate gene-editing, a target sequence within the marker tor pigment gene was chosen, and gene-editing was predicted to result in white pigmentation in the offspring of treated adult aphids. Adult aphids (10-d old) were injected with the tor single guide RNA and Cas9 complex and subsequently subjected to electroporation. Adult aphids were given 4 d to produce viviparous offspring. After offspring developed for 6 d, DNA was extracted and sequenced to validate if CRISPR/Cas9-directed gene editing occurred. A survival rate over 70% was found in treated adult aphids. A distinct white pigmentation was found in 2.5% of aphids; however, gene-editing within the target sequence was not found in any of the individuals screened. Presence of white aphids without gene-editing suggests other mechanisms may have influenced pigmentation. High survival rates in experimental treatments demonstrate the robustness of this new technique, and further refinement of this technique may prove it as an effective functional genomics tool for viviparous insects and/or gene editing at a somatic level.

Helios(®) Gene Gun-Mediated Transfection of the Inner Ear Sensory Epithelium: Recent Updates

The transfection of vertebrate inner ear hair cells has proven to be challenging. Therefore, many laboratories attempt to use and improve different transfection methods. Each method has its own advantages and disadvantages. A particular researcher's skills in addition to available equipment and the type of experiment (in vivo or in vitro) likely determine the transfection method of choice. Biolistic delivery of exogenous DNA, mRNA, or siRNA, also known as Helios(®) Gene Gun-mediated transfection, uses the mechanical energy of compressed helium gas to bombard tissue with micron- or submicron-sized DNA or RNA-coated gold particles, which can penetrate and transfect cells in vitro or in vivo. Helios(®) Gene Gun-mediated transfection has several advantages: (1) it is simple enough to learn in a short time; (2) it is designed to overcome cell barriers even as tough as plant cell membrane or stratum corneum in the epidermis; (3) it can transfect cells deep inside a tissue such as specific neurons within a brain slice; (4) it can accommodate mRNA, siRNA, or DNA practically of any size to be delivered; and (5) it works well with various cell types including non-dividing, terminally differentiated cells that are difficult to transfect, such as neurons or mammalian inner ear sensory hair cells. The latter advantage is particularly important for inner ear research. The disadvantages of this method are: (1) low efficiency of transfection due to many variables that have to be adjusted and (2) potential mechanical damage of the tissue if the biolistic shot parameters are not optimal. This chapter provides a step-by-step protocol and critical evaluation of the Bio-Rad Helios(®) Gene Gun transfection method used to deliver green fluorescent protein (GFP)-tagged full-length cDNAs of myosin 15a, whirlin, β-actin, and Clic5 into rodent hair cells of the postnatal inner ear sensory epithelia in culture.

Optimization of a plasma facilitated DNA delivery method

Plasma-based methods have recently emerged as a technique for augmenting plasmid DNA delivery to skin. This delivery modality relies on the deposition of ionized gas molecules on to targeted cells or tissue to establish an electric field. It is hypothesized that this electric field results in the dielectric breakdown of cell membranes, making cells permeable to exogenous molecules. This in vivo investigation sought to optimize the intradermal delivery of a luciferase expressing plasmid DNA by modulating the total exposure to the plasma source and the plasmid DNA dose. Varying the plasma exposure time from 2, 5, 10, and 20 min allowed the conditions resulting in the highest expression of luciferase to be found. These conditions correlated to the 10 minute exposure time for a plasma derived from either +8 kV or -8 kV, when the generator was operated 3 cm from the epidermal tissue surface with a helium flow rate of 15 L/min. Exposing the injected flank skin for 10 min resulted in a rise of 37.3-fold for a plasma created with +8 kV and 27.1-fold for a plasma created with -8 kV. When using this treatment time with 50, 100, or 200 μg of a luciferase expressing plasmid, it was found that 100 μg resulted in the highest peak luminescence.

Targeted gene delivery in the cricket brain, using in vivo electroporation

The cricket (Gryllus bimaculatus) is a hemimetabolous insect that is emerging as a model organism for the study of neural and molecular mechanisms of behavioral traits. However, research strategies have been limited by a lack of genetic manipulation techniques that target the nervous system of the cricket. The development of a new method for efficient gene delivery into cricket brains, using in vivo electroporation, is described here. Plasmid DNA, which contained an enhanced green fluorescent protein (eGFP) gene, under the control of a G. bimaculatus actin (Gb'-act) promoter, was injected into adult cricket brains. Injection was followed by electroporation at a sufficient voltage. Expression of eGFP was observed within the brain tissue. Localized gene expression, targeted to specific regions of the brain, was also achieved using a combination of local DNA injection and fine arrangement of the electroporation electrodes. Further studies using this technique will lead to a better understanding of the neural and molecular mechanisms that underlie cricket behaviors.

Novel middle-type Kenyon cells in the honeybee brain revealed by area-preferential gene expression analysis

The mushroom bodies (a higher center) of the honeybee (Apis mellifera L) brain were considered to comprise three types of intrinsic neurons, including large- and small-type Kenyon cells that have distinct gene expression profiles. Although previous neural activity mapping using the immediate early gene kakusei suggested that small-type Kenyon cells are mainly active in forager brains, the precise Kenyon cell types that are active in the forager brain remain to be elucidated. We searched for novel gene(s) that are expressed in an area-preferential manner in the honeybee brain. By identifying and analyzing expression of a gene that we termed mKast (middle-type Kenyon cell-preferential arrestin-related protein), we discovered novel ‘middle-type Kenyon cells’ that are sandwiched between large- and small-type Kenyon cells and have a gene expression profile almost complementary to those of large– and small-type Kenyon cells. Expression analysis of kakusei revealed that both small-type Kenyon cells and some middle-type Kenyon cells are active in the forager brains, suggesting their possible involvement in information processing during the foraging flight. mKast expression began after the differentiation of small- and large-type Kenyon cells during metamorphosis, suggesting that middle-type Kenyon cells differentiate by modifying some characteristics of large– and/or small-type Kenyon cells. Interestingly, CaMKII and mKast, marker genes for large– and middle-type Kenyon cells, respectively, were preferentially expressed in a distinct set of optic lobe (a visual center) neurons. Our findings suggested that it is not simply the Kenyon cell-preferential gene expression profiles, rather, a ‘clustering’ of neurons with similar gene expression profiles as particular Kenyon cell types that characterize the honeybee mushroom body structure.

Honey bee promoter sequences for targeted gene expression

The honey bee, Apis mellifera, displays a rich behavioural repertoire, social organization and caste differentiation, and has an interesting mode of sex determination, but we still know little about its underlying genetic programs. We lack stable transgenic tools in honey bees that would allow genetic control of gene activity in stable transgenic lines. As an initial step towards a transgenic method, we identified promoter sequences in the honey bee that can drive constitutive, tissue-specific and cold shock-induced gene expression. We identified the promoter sequences of Am-actin5c, elp2l, Am-hsp83 and Am-hsp70 and showed that, except for the elp2l sequence, the identified sequences were able to drive reporter gene expression in Sf21 cells. We further demonstrated through electroporation experiments that the putative neuron-specific elp2l promoter sequence can direct gene expression in the honey bee brain. The identification of these promoter sequences is an important initial step in studying the function of genes with transgenic experiments in the honey bee, an organism with a rich set of interesting phenotypes.

Characterization of plasma mediated molecular delivery to cells in vitro

Ion-based strategies have recently emerged as a method to facilitate molecular delivery. These methods are attractive as they separate the applicator from the treatment site avoiding some issues encountered with other electrically driven methods. Current literature on plasma delivery has shown utility in vitro and in vivo for both drugs and genes. To advance this technology more information must become available on the mechanism responsible for delivery and the effects of ion exposure on eukaryotic cells. This in vitro investigation found that molecular delivery facilitated by a DC-based plasma follows a dose-response behavior, with optimum uptake of Sytox Green occurring in two cell lines after 600 s of exposure. In both cell lines exposure to the discharge caused no adverse effects in viability for exposure times up to 600 s. It was also found that membranes treated with ions remained permeabilized for several minutes following plasma treatment and that membrane resealing exhibited first order kinetics.

Plasma facilitated delivery of DNA to skin

Non-viral delivery of cell-impermeant drugs and DNA in vivo has traditionally relied upon either chemical or physical stress applied directly to target tissues. Physical methods typically use contact between an applicator, or electrode, and the target tissue and may involve patient discomfort. To overcome contact-dependent limitations of such delivery methodologies, an atmospheric helium plasma source was developed to deposit plasma products onto localized treatment sites. Experiments performed in murine skin showed that samples injected with plasmid DNA encoding luciferase and treated with plasma demonstrated increased levels of expression relative to skin samples that received injections of DNA alone. Increased response relative to injection alone was observed when either positive or negative voltage was used to generate the helium plasma. Quantitative results over a 26-day follow-up period showed that luciferase levels as high as 19-fold greater than the levels obtained by DNA injection alone could be achieved. These findings indicate that plasmas may compete with other physical delivery methodologies when skin is the target tissue.

How functional genomics and genetics complements insect endocrinology

Insects are the most abundant animal group on Earth and have been the subject of genetic and physiological studies since the beginning of the 19th century. The public interest in understanding their biology increased as many insects have proven to exert a severe impact on human welfare and the environment. To trigger insect physiological and endocrinological research, the genome of several economical and ecological important insect species was recently sequenced. Following the availability of these genomic data many so called 'post-genomic' technologies have been developed to characterise gene function and to unravel signalling pathways underlying biological processes. For some species genomic research is further complemented with mutagenesis and reverse genetic studies. In the following, we present an overview of genomic and functional genetic methodologies that boosted endocrine research in insects.

In-vivo gene transfer into newly hatched chick brain by electroporation

Newly hatched domestic chicks serve as ideal models for studies of the neural basis of behavioral plasticity, particularly for understanding the mechanisms of learning such as filial imprinting. To elucidate the molecular basis and gene functions involved in learning, we developed an in-vivo gene-transfer system in the brain of a living chick using electroporation. When green fluorescent protein-encoding plasmids were transfected to a chick brain, green fluorescence was clearly observed, and expression at the protein level was confirmed by immunoblotting. Most of the transfected brain cells were neuronal cells with dendrites. This neuron-selective electroporation system will facilitate the analysis of gene functions in the living chick brain and provide further clues as to the molecular mechanisms of avian learning.

In vivo gene transfer into the honeybee using a nucleopolyhedrovirus vector

The honeybee Apis mellifera L. is a social insect and one of the most industrially important insects. We examined whether a baculovirus-mediated retrotransposon is applicable to in vivo transfer of exogenous genes to the honeybees. Honeybee larvae and pupae were injected with two types of recombinant Autographa californica nucleopolyhedrovirus (AcNPV) vectors, one that includes the enhanced green fluorescent protein gene (egfp) as a reporter to be inserted into the honeybee genome, and another that includes the reverse transcriptase gene responsible for the insertion. Fluorescence was observed in most of the viral-injected larvae and pupae. Reverse transcription-polymerase chain reaction and immunoblotting confirmed egfp mRNA and eGFP expression in these honeybees, although egfp insertion into the honeybee genome was not confirmed. These results indicate that AcNPV vectors can be used for the transfer and transient expression of an exogenous gene in the larval and pupal honeybees.

Small brains, bright minds

Learning, memory, and social behavior are innate properties of the honeybee that are essential for the survival of each individual as well as for the survival of the hive. The small, accessible brain of the honeybee and the availability of the complete sequence of its genome make this social insect an ideal model for studying the connection between learning, memory, and social behavior.

Associative visual learning, color discrimination, and chromatic adaptation in the harnessed honeybee Apis mellifera L

We studied associative visual learning in harnessed honeybees trained with monochromatic lights associated with a reward of sucrose solution delivered to the antennae and proboscis, to elicit the proboscis extension reflex (PER). We demonstrated five properties of visual learning under these conditions. First, antennae deprivation significantly increased visual acquisition, suggesting that sensory input from the antennae interferes with visual learning. Second, covering the compound eyes with silver paste significantly decreased visual acquisition, while covering the ocelli did not. Third, there was no significant difference in the visual acquisition between nurse bees, guard bees, and foragers. Fourth, bees conditioned with a 540-nm light stimulus exhibited light-induced PER with a 618-nm, but not with a 439-nm light stimulus. Finally, bees conditioned with a 540-nm light stimulus exhibited PER immediately after the 439-nm light was turned off, suggesting that the bees reacted to an afterimage induced by prior adaptation to the 439-nm light that might be similar to the 540-nm light.

Identification and analysis of the minimal promoter activity of a novel noncoding nuclear RNA gene, AncR-1, from the honeybee (Apis mellifera L.)

Previously, we identified a gene for a noncoding nuclear RNA, termed Ks-1, that is expressed preferentially in a restricted set of neurons in the honeybee brain. In the present study, we identified another novel gene, termed AncR-1, whose transcripts were localized to nuclei in the whole cortex region of the honeybee brain, as a candidate novel noncoding nuclear RNA gene. RNA fluorescent in situ hybridization revealed that AncR-1 and Ks-1 transcripts were located in a distinct portion of a single neural nucleus, suggesting that they have distinct functions in brain neurons. cDNA cloning revealed that the AncR-1 transcripts were up to 7 kb in size, had mRNA-like structures, and were alternatively spliced. The reporter assay using Drosophila SL-2 cells demonstrated that a TATA box-like sequence located -30 bp upstream of the 5' end of AncR-1 cDNA had promoter activity. None of the alternatively spliced AncR-1 cDNA variants contained significant open reading frames, strongly suggesting that AncR-1 transcripts function as novel noncoding nuclear RNAs. Furthermore, in situ hybridization revealed that AncR-1 was expressed not only in the brain but also in the sex organs in the queen and drones and in the hypopharyngeal glands and oenocytes of the worker bees, suggesting that AncR-1 is involved in diverse organ functions. Some of the AncR-1 transcripts enriched in the nuclei of the hypopharyngeal glands were polyadenylated, indicating the presence of mRNA-like AncR-1 transcripts in the nuclei.