Creating Avian Forebrain Chimeras to Assess Facial Development
February 18th, 2021
This article describes a tissue transplantation technique that was designed to test the signaling and patterning properties of basal forebrain during craniofacial development.
This method allows investigators to assess tissue interactions between the basal forebrain and the face. The main advantage of this technique is that it isolates the basal forebrain for assessment and prevents contamination with neural crest cells, which would confound the analysis. The difficult part of this technique is the removal of the forebrain from the host and replacement with the donor tissue.
Demonstrating the procedure will be Diane Hu, a research scientist from Dr.Ralph Marcucio's laboratory. To begin, prepare DMEM media with neutral red, a glass transfer pipette, and sharpened tungsten. Using a 10 milliliter syringe and an 18 gauge needle, remove 0.5 milliliters of albumin from the pointed end of the eggshell.
Make a small hole on top of the shell using the point of scissors. Then place a piece of tape over the hole and cut a circular opening to expose the embryo. Stain the embryo with neutral red.
Harvest tissue grafts from the left side of the basal forebrain of stage seven or eight embryos. Use curved sharpened tungsten needles to gently incise a piece of the forebrain. In order to not include the underlying endoderm, slide the needle beneath the forebrain and parallel to the axis of the neural tube.
Pick the graft up from the donor embryo using the glass transfer pipette, and transfer it into DMEM containing neutral red for two minutes to stain it. Then place the stained graft into DMEM that does not contain neutral red until ready for engraftment. Incubate fertilized eggs from white Leghorn chicken at 37 degrees Celsius in a humidified chamber until Hamburger-Hamilton stage seven to eight.
Expose embryos as previously demonstrated. Using sharpened tungsten needles, prepare the graft site by cutting and then removing a 0.3 by 0.2 millimeter piece of basal forebrain to accommodate the graft. Avoid excessive disruption of the underlying endoderm, which will be evident as yolk granules will begin to leak through any tear that is made.
After transferring the graft to the host, position the graft to replace the extirpated basal forebrain of the host. Place tape tightly over the hole, and return the embryos to the 37 degree Celsius incubator until they are ready for analysis. Initially, chimeras were created by transplanting quail tissues into chick embryos.
Using the QCPN antibody, quail cells were visualized and distinguished from the host tissues. The quail-chick system confirmed that all of the graft was comprised only of neural tissue and was not contaminated with other cell types. Transplantation of quail tissue into duck embryos led to severely deformed chimeras due to a faster developing quail brain.
Therefore, transplantation of duck tissues into chicken embryos was performed. The resulting duck-chick chimeras suggest that the brain participates in regulating morphology. Whole mountain C2 hybridization was used to assess Sonic hedgehog expression in chimeras.
Similar to morphology, Sonic hedgehog expression on the duck side of the chimera appeared more duck-like. Preparing the host site takes practice. A large number of embryos do not survive, so creating a large number of chimeras can help ensure proper samples for analysis.
This method made it possible to assess how signals from the brain shape the Sonic hedgehog expression domain in the frontonasal ectodermal zone.
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Overview
This article describes a tissue transplantation technique that allows investigators to assess tissue interactions between the basal forebrain and the face during craniofacial development. The method isolates the basal forebrain for assessment, preventing contamination with neural crest cells.
Key Study Components
Area of Science
- Neuroscience
- Craniofacial Development
- Tissue Transplantation Techniques
Background
- The basal forebrain plays a critical role in craniofacial development.
- Understanding tissue interactions is essential for developmental biology.
- Contamination from neural crest cells can confound analysis.
- Isolating the basal forebrain allows for clearer assessment of its signaling properties.
Purpose of Study
- To test the signaling and patterning properties of the basal forebrain.
- To develop a reliable method for tissue transplantation.
- To enhance understanding of craniofacial development mechanisms.
Methods Used
- Preparation of DMEM media with neutral red.
- Use of a glass transfer pipette and sharpened tungsten.
- Removal of albumin from the pointed end of the eggshell using a syringe.
- Replacement of the host forebrain with donor tissue.
Main Results
- The technique effectively isolates the basal forebrain for analysis.
- Demonstration of the procedure by a research scientist.
- Successful assessment of tissue interactions without contamination.
- Insights into the role of the basal forebrain in craniofacial development.
Conclusions
- The transplantation technique is a valuable tool for studying craniofacial development.
- Isolating the basal forebrain enhances the accuracy of developmental assessments.
- This method can be applied to further research in developmental neuroscience.
Frequently Asked Questions
Executive Industry Relevance
This method enables precise assessment of tissue signaling in craniofacial development by isolating the basal forebrain from confounding neural crest contributions. It supports mechanistic de-risking in target validation by clarifying how brain-derived signals regulate morphogenetic pathways like Sonic hedgehog in the frontonasal ectodermal zone. The approach provides a disease-relevant system for evaluating developmental pathways with predictive confidence in early discovery.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Interrogates therapeutic hypotheses about brain-facial tissue interactions in vertebrate development.
- Operational Value: Enables functional target validation by isolating basal forebrain signaling properties.
- Predictive Value: Supports predictive confidence by linking basal forebrain manipulation to SHH expression domain changes.
Screening & Assay Development
- Scientific Value: Prepares validated chimeric systems for quantitative assessment of morphogen expression.
- Operational Value: Standardizes tissue transplantation for reproducible assay readouts across experimental conditions.
- Scalability: Facilitates generation of multiple chimeras to overcome low survival rates and ensure analytical robustness.
Translational & Preclinical Research
- Translational Continuity: Connects discovery-stage mechanistic insights to preclinical models of craniofacial patterning.
- Mechanistic De-risking: Clarifies upstream regulators of SHH, a key pathway in congenital disorder modeling.
- Disease-Relevant System: Uses avian chimeras to study conserved vertebrate facial development mechanisms.
Pipeline & Workflow Integration
The method fits within early discovery workflows where tissue interaction assays inform target confidence before lead identification efforts.
- Discovery Biology: Supports hypothesis testing of signaling centers in craniofacial morphogenesis.
- Assay Readiness: Generates standardized biological systems for quantitative SHH expression analysis.
- Analytics: Enables whole-mount in situ hybridization to measure spatial gene expression changes as a key readout.
- Translational Research: Provides mechanistic continuity from neural tissue grafting to facial phenotype outcomes.
- Enterprise Reuse: Establishes a reusable platform for assessing tissue-specific contributions to developmental pathways.
Operational & Enterprise Impact
- Scientific Value: Reduces mechanistic ambiguity by isolating basal forebrain signals in facial development.
- Operational Value: Ensures reproducibility through standardized grafting and host preparation techniques.
- Strategic Value: Improves go/no-go decisions by clarifying upstream regulators of druggable pathways like SHH.
- Portfolio Impact: Enables risk-adjusted prioritization of targets based on validated tissue interaction data.
Implementation Considerations
- Requires expertise in microsurgical tissue handling and avian embryo manipulation.
- Dependent on specialized tools including sharpened tungsten needles and glass transfer pipettes.
- Necessitates standardized incubation and staging protocols for host and donor embryos.
- Involves optimization of graft site preparation to prevent yolk leakage and ensure host viability.
- Limited by low embryo survival rates, necessitating high sample numbers for reliable analysis.
