Biological Sciences

Measuring autonomic parameters like heart rate in behaving mice is not only a standard procedure in cardiovascular research but is applied in many other interdisciplinary research fields. With an electrocardiogram (ECG), the heart rate can be measured by deriving the electrical potential between subcutaneously implanted wires across the chest. This is an inexpensive and easy-to-implement technique and particularly suited for repeated recordings of up to eight weeks. This protocol describes a step-by-step guide for manufacturing the needed equipment, performing the surgical procedure of electrode implantation, and processing of acquired data, yielding accurate and reliable detection of heartbeats and calculation of heart rate (HR). We provide MATLAB graphical user interface (GUI)–based tools to extract and start processing the acquired data without a lot of coding knowledge. Finally, based on an example of a data set acquired in the context of defensive reactions, we discuss the potential and pitfalls in analyzing HR data.

Key features

• Next to surgical steps, the protocol provides a detailed description of manufacturing custom-made ECG connectors and a shielded, light-weight patch cable.

• Suitable for recordings in which signal quality is challenged by ambient noise or noise from other recording devices.

• Described for 2-channel differential recording but easily expandable to record from more channels.

• Includes a summary of potential analysis methods and a discussion on the interpretation of HR dynamics in the case study of fear states.

Seeds ensure the growth of a new generation of plants and are thus central to maintaining plant populations and ecosystem processes. Nevertheless, much remains to be learned about seed biology and responses of germinated seedlings to environmental challenges. Experiments aiming to close these knowledge gaps critically depend on the availability of healthy, viable seeds. Here, we report a protocol for the collection of seeds from plants in the genus Populus. This genus comprises trees with a wide distribution in temperate forests and with economic relevance, used as scientific models for perennial plants. As seed characteristics can vary drastically between taxonomic groups, protocols need to be tailored carefully. Our protocol takes the delicate nature of Populus seeds into account. It uses P. deltoides as an example and provides a template to optimize bulk seed extraction for other Populus species and plants with similar seed characteristics. The protocol is designed to only use items available in most labs and households and that can be sterilized easily. The unique characteristics of this protocol allow for the fast and effective extraction of high-quality seeds. Here, we report on seed collection, extraction, cleaning, storage, and viability tests. Moreover, extracted seeds are well suited for tissue culture and experiments under sterile conditions. Seed material obtained with this protocol can be used to further our understanding of tree seed biology, seedling performance under climate change, or diversity of forest genetic resources.

Key features

• Populus species produce seeds that are small, delicate, non-dormant, with plenty of seed hair. Collection of seed material needs to be timed properly.

• Processing, seed extraction, seed cleaning, and storage using simple, sterilizable laboratory and household items only. Obtained seeds are pure, high quality, close to 100% viability.

• Seeds work well in tissue culture and in experiments under sterile conditions.

• Extractability, speed, and seed germination were studied and confirmed for Populus deltoides as an example.

• Can also serve as template for bulk seed collection from other Populus species and plant groups that produce delicate seeds (with no or little modifications).

Graphical overview

Fusarium oxysporum can cause many important plant diseases worldwide, such as crown rot, wilt, and root rot. During the development of strawberry crown rot, this pathogenic fungus spreads from the mother plant to the strawberry seedling through the stolon, with obvious characteristics of latent infection. Therefore, the rapid and timely detection of F. oxysporum can significantly help achieve effective disease management. Here, we present a protocol for the recombinase polymerase amplification– lateral flow dipstick (RPA–LFD) detection technique for the rapid detection of F. oxysporum on strawberry, which only takes half an hour. A significant advantage of our RPA–LFD technique is the elimination of the involvement of professional teams and laboratories, which qualifies it for field detection. We test this protocol directly on plant samples with suspected infection by F. oxysporum in the field and greenhouse. It is worth noting that this protocol can quickly, sensitively, and specifically detect F. oxysporum in soils and plants including strawberry.

Key features

• This protocol is used to detect whether plants such as strawberry are infected with F. oxysporum.

• This protocol has potential for application in portable nucleic acid detection.

• It can complete the detection of samples in the field within 30 min.

Graphical overview

Toxoplasma gondii is a zoonotic protozoan parasite and one of the most successful foodborne pathogens. Upon infection and dissemination, the parasites convert into the persisting, chronic form called bradyzoites, which reside within cysts in muscle and brain tissue. Despite their importance, bradyzoites remain difficult to investigate directly, owing to limited in vitro models. In addition, the need for new drugs targeting the chronic stage, which is underlined by the lack of eradicating treatment options, remains difficult to address since in vitro access to drug-tolerant bradyzoites remains limited. We recently published the use of a human myotube-based bradyzoite cell culture system and demonstrated its applicability to investigate the biology of T. gondii bradyzoites. Encysted parasites can be functionally matured during long-term cultivation in these immortalized cells and possess many in vivo–like features, including pepsin resistance, oral infectivity, and antifolate resistance. In addition, the system is scalable, enabling experimental approaches that rely on large numbers, such as metabolomics. In short, we detail the cultivation of terminally differentiated human myotubes and their subsequent infection with tachyzoites, which then mature to encysted bradyzoites within four weeks at ambient CO₂ levels. We also discuss critical aspects of the procedure and suggest improvements.

Key features

• This protocol describes a scalable human myotube-based in vitro system capable of generating encysted bradyzoites featuring in vivo hallmarks.

• Bradyzoite differentiation is facilitated through CO₂ depletion but without additional artificial stress factors like alkaline pH.

• Functional maturation occurs over four weeks.

Graphical overview

Recent advancements in chemogenetic tools, such as designer receptors exclusively activated by designer drugs (DREADDs), allow the simultaneous manipulation of activity over a specific, broad brain region in nonhuman primates. However, the introduction of DREADDs into large and complexly shaped cortical sulcus regions of macaque monkeys is technically demanding; previously reported methods are time consuming or do not allow the spatial range of expression to be controlled. In the present report, we describe the procedure for an adeno-associated viral vector (AAV2.1) delivery via handheld injections into the dorsolateral prefrontal cortex (Brodmann’s area 9/46) of macaque monkeys, with reference to pre-scanned anatomical magnetic resonance images. This procedure allows the precise delivery of DREADDs to a specific cortical region.

Key features

• This article describes the procedures for injecting viral vectors encoding functional proteins for chemogenetic manipulation into targeted cortical sulcus regions.

• The protocol requires magnetic resonance imaging for the accurate estimation of the injection sites prior to surgery.

• Viral vector solutions are injected using a handheld syringe under microscopic guidance.

• This protocol allows for the precise introduction of designer receptors exclusively activated by designer drugs (DREADDs) to large and complex cortical regions.

Dolichyl phosphates (DolP) are ubiquitous lipids that are present in almost all eukaryotic membranes. They play a key role in several protein glycosylation pathways and the formation of glycosylphosphatidylinositol anchors. These lipids constitute only ~0.1% of total phospholipids, and their analysis by reverse phase (RP) liquid chromatography–high-resolution mass spectrometry (LC–HRMS) is challenging due to their high lipophilicity (log P > 20), poor ionization efficiency, and relatively low abundance. To overcome these challenges, we have introduced a new approach for DolP analysis by combining trimethylsilyldiazomethane (TMSD)-based phosphate methylation and HRMS analysis. The analytical method was validated for its reproducibility, sensitivity, and accuracy. The established workflow was successfully applied for the simultaneous characterization and quantification of DolP species with different isoprene units in lipid extracts of HeLa and Saccharomyces cerevisiae cells.

Campylobacter jejuni, a zoonotic foodborne pathogen, is the worldwide leading cause of acute human bacterial gastroenteritis. Biofilms are a significant reservoir for survival and transmission of this pathogen, contributing to its overall antimicrobial resistance. Natural compounds such as essential oils, phytochemicals, polyphenolic extracts, and D-amino acids have been shown to have the potential to control biofilms formed by bacteria, including Campylobacter spp. This work presents a proposed guideline for assessing and characterizing bacterial biofilm formation in the presence of naturally occurring inhibitory molecules using C. jejuni as a model. The following protocols describe: i) biofilm formation inhibition assay, designed to assess the ability of naturally occurring molecules to inhibit the formation of biofilms; ii) biofilm dispersal assay, to assess the ability of naturally occurring inhibitory molecules to eradicate established biofilms; iii) confocal laser scanning microscopy (CLSM), to evaluate bacterial viability in biofilms after treatment with naturally occurring inhibitory molecules and to study the structured appearance (or architecture) of biofilm before and after treatment.

Brain organoids have been widely used to study diseases and the development of the nervous system. Many reports have investigated the application of brain organoids, but most of these models lack vascular structures, which play essential roles in brain development and neurological diseases. The brain and blood vessels originate from two different germ layers, making it difficult to induce vascularized brain organoids in vitro. We developed this protocol to generate brain-specific blood vessel and cerebral organoids and then fused them at a specific developmental time point. The fused cerebral organoids exhibited robust vascular network-like structures, which allows simulating the in vivo developmental processes of the brain for further applications in various neurological diseases.

Key Features

• Culturing vascularized brain organoids using human embryonic stem cells (hESCs).

• The new approach generates not only neural cells and vessel-like networks but also brain-resident microglia immune cells in a single organoid.

Graphical overview

Workflow and timeline for vessel organoid and vascularized brain organoid generation. (By Figdraw, ID: RTIURffccf)

Strawberries are delicious and nutritious fruits that are widely cultivated and consumed around the world, either fresh or in various products such as jam, juice, and ice cream. Botrytis cinerea is a fungal pathogen that causes gray mold disease on many crops, including strawberries. Disease monitoring is an important aspect for growing commercial crops like strawberry because there is an urgent need to develop effective strategies to control this destructive gray mold disease. In this protocol, we provide an important tool to monitor the gray mold fungal infection progression in different developmental stages of strawberry. There are different types of inoculation assays for B. cinerea on strawberry plants, such as in vitro (in/on a culture medium) or in vivo (in a living plant). In vivo inoculation assays can be performed at early, middle, and late stages of strawberry development. Here, we describe three methods for in vivo inoculation assays of B. cinerea on strawberry plants. For early-stage strawberry plants, we modified the traditional fungal disc inoculation method to apply to fungal infection on strawberry leaves. For middle-stage strawberry plants, we developed the flower infection assay by dropping fungal conidia onto flowers. For late-stage strawberry plants, we tracked the survival rate of strawberry fruits after fungal conidia infection. This protocol has been successfully used in both lab and greenhouse conditions. It can be applied to other flowering plants or non-model species with appropriate modifications.

Key features

• Fungal disc inoculation on early-stage strawberry leaves.

• Fungal conidia inoculation on middle-stage strawberry flowers.

• Disease rating for late-stage strawberry fruits.

• This protocol is applicable to the other flowering plants with appropriate modifications.

Graphical overview

In vivo infection progression assays of gray mold fungus Botrytis cinerea at different developmental stages of strawberry. Created with BioRender.com.

Fertilized teleost fish eggs are a complex formation, in which dividing cells arelocated in a small point in the entire volume of eggs. Isolating embryonic cellscan be considered a necessary step in the research of developmentalpeculiarities of fish cells at the earliest stages of embryogenesis beforeembryo formation. The main advantages of the offered protocol are rapidisolation, no enzymes, and overall low cost compared to other protocols. Theprotocol is suitable for the isolation of embryonic cells from medium-sized eggsat the stages of blastula or gastrula, for studies in a variety of applications(e.g., microscopy, flow cytometry, and other methods). Fertilized nelma eggs(Stenodus leucichthys nelma) are used in the protocol as a model.

Key features

• Fast and cheap isolation of cells from fish eggs at early stages (blastula orgastrula).

• Applicable for most of the methods for cell study (any staining, microscopy, flowcytometry, etc.).

• Can be applied to other teleost fish eggs with medium egg diameter of 3–4mm.

Graphical overview