GO:0007368 determination of left/right symmetry: Embryonic Axis Patterning, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0007368 describes the biological process that establishes an organism's body plan with respect to the left and right halves, producing either symmetric or asymmetric patterns.
• In vertebrates, left-right symmetry breaking is initiated by cilia-driven fluid flow at the embryonic node, which is sensed by immotile cilia and translated into asymmetric gene expression.
• The interplay of planar cell polarity, calcium signaling, and cilia is central to breaking left-right symmetry.
• Nodal, Lefty, and Pitx2 form a conserved left-sided signaling cascade that propagates asymmetry from the node to developing organs.
• KIF3 molecular motors are required for cilia assembly and nodal flow, linking intracellular transport to left-right determination.
• Disruption of left-right symmetry genes causes heterotaxy, situs inversus, and congenital heart defects, making this process clinically important.
Description
Determination of left/right symmetry (GO:0007368) is the biological process that establishes an organism's body plan or part of an organism with respect to the left and right halves, resulting in either a symmetric pattern where the halves are mirror images or an asymmetric pattern that deviates from this symmetry. This process is fundamental to embryonic development, as it ensures that internal organs such as the heart, liver, and spleen are positioned correctly along the left-right axis. In vertebrates, the initial symmetry break occurs at the embryonic node, where motile cilia generate a leftward fluid flow that is sensed by immotile cilia, triggering asymmetric calcium signaling and gene expression. The coordination of planar cell polarity, calcium signaling, and cilia function is essential for this symmetry-breaking event. Researchers study GO:0007368 to understand congenital disorders such as heterotaxy and situs inversus, as well as to uncover general principles of how embryos pattern their body axes. The molecular motor KIF3 and its role in cilia assembly further highlight the importance of intracellular transport in left-right determination.
determination of left/right symmetry At A Glance
| GO ID | GO:0007368 |
|---|---|
| GO term | determination of left/right symmetry |
| Ontology | biological_process |
| Synonym | determination of left/right asymmetry |
| Major function | Establishment of body plan with respect to left and right halves, producing symmetric or asymmetric patterns |
| Key cellular structures | Motile and immotile cilia at the embryonic node |
| Core signaling molecules | Nodal, Lefty, Pitx2, KIF3 |
| Associated diseases | Heterotaxy, situs inversus, congenital heart defects |
What Is GO:0007368?
In our own words, GO:0007368 encompasses all molecular and cellular events that assign left and right identities to an organism or its parts. It includes the initial breaking of symmetry, the propagation of asymmetric signals, and the stabilization of left-right differences in developing tissues. The outcome can be symmetric (mirror-image halves) or asymmetric (deviating from mirror symmetry), as defined by the Gene Ontology.
Why Is determination of left/right symmetry Important in Cell Biology?
Understanding GO:0007368 is crucial because defects in left-right symmetry determination lead to severe congenital disorders, including heterotaxy and situs inversus, which are often accompanied by complex heart malformations. The process also serves as a paradigm for how mechanical forces and chemical signals integrate to pattern the embryo, offering insights into general principles of developmental biology.
• Mutations in left-right symmetry genes cause heterotaxy and situs inversus, affecting organ placement.
• Congenital heart defects are frequently associated with abnormal left-right patterning.
• Cilia dysfunction links left-right determination to ciliopathies such as primary ciliary dyskinesia.
• The process exemplifies mechanosensing, where fluid flow is converted into biochemical signals.
• Planar cell polarity and calcium signaling are key modulators of symmetry breaking.
• KIF3 motor proteins are essential for cilia assembly and nodal flow.
• Zebrafish and mouse models provide powerful systems to study left-right asymmetry.
• Research on GO:0007368 informs regenerative medicine and tissue engineering of asymmetric organs.
What Happens During determination of left/right symmetry?
Initiation at the embryonic node
In simple terms: The embryo first decides left from right at a tiny structure called the node.
In vertebrates, the embryonic node contains motile cilia that rotate to generate a leftward fluid flow. This flow is the initial symmetry-breaking event, as it creates a directional cue that distinguishes left from right. The mechanical regulation by nodal cilia is critical for initiating asymmetry.
Sensing of fluid flow by immotile cilia
In simple terms: Special antenna-like cilia sense the direction of the fluid flow.
Immotile cilia at the node act as mechanosensors that detect the direction of fluid flow. They translate this mechanical stimulus into asymmetric calcium signaling, which is essential for left-right determination. This sensory function is distinct from the motile cilia that generate the flow.
Calcium signaling and planar cell polarity
In simple terms: Calcium signals and cell polarity help spread the left-right message.
The interplay between planar cell polarity, calcium signaling, and cilia is required for breaking left-right symmetry. Calcium signals propagate asymmetric information, while planar cell polarity coordinates cell orientation and tissue-level asymmetry.
Asymmetric gene expression cascade
In simple terms: A cascade of genes turns on only on the left side.
The initial cues lead to left-sided expression of Nodal, which induces Lefty and Pitx2. This conserved cascade propagates asymmetry from the node to developing organs, ensuring proper left-right positioning. Nodal acts as a morphogen, and its feedback inhibitor Lefty restricts its activity.
Tissue-level morphogenesis
In simple terms: Cells and tissues physically rearrange to form asymmetric organs.
Downstream of gene expression, asymmetric cell behaviors such as differential proliferation, migration, and extracellular matrix remodeling shape organs like the heart and gut. In zebrafish, somite surface tension is required for left-right symmetry of the embryo, highlighting the role of tissue mechanics.
Key Genes Involved in GO:0007368 determination of left/right symmetry
The following genes and proteins are central to the determination of left/right symmetry, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| Nodal | Left-sided morphogen that induces asymmetric gene expression | Key marker of left-right asymmetry; mutations cause heterotaxy |
| Lefty | Feedback inhibitor of Nodal, restricts its activity | Regulates the extent of left-sided signaling |
| Pitx2 | Transcription factor downstream of Nodal | Effector of left-sided identity in organs |
| KIF3 | Molecular motor required for cilia assembly and nodal flow | Links intracellular transport to left-right determination |
| Dnah5 | Axonemal dynein heavy chain, required for motile cilia | Mutations cause primary ciliary dyskinesia and situs inversus |
| Pkd2 | Calcium channel involved in flow sensing | Mediates calcium signaling at the node |
| Vangl1 | Planar cell polarity component | Coordinates tissue-level asymmetry |
| Vangl2 | Planar cell polarity component | Coordinates tissue-level asymmetry |
| Celsr1 | Planar cell polarity component | Coordinates tissue-level asymmetry |
| Bbs proteins | Cilia trafficking and assembly | Ciliopathy-related left-right defects |
| Ift88 | Intraflagellar transport protein | Required for cilia formation and nodal flow |
| Zic3 | Transcription factor involved in left-right patterning | Mutations associated with heterotaxy |
| Acvr2b | Receptor for Nodal signaling | Mediates Nodal signal transduction |
| Smad2 | Intracellular transducer of Nodal signaling | Phosphorylated Smad2 marks left-sided signaling |
| Foxj1 | Master regulator of motile ciliogenesis | Controls cilia formation at the node |
| Rfx3 | Transcription factor regulating cilia genes | Affects nodal cilia and left-right asymmetry |
| Ccdc39 | Cilia and flagella associated protein | Mutations linked to primary ciliary dyskinesia |
How Is determination of left/right symmetry Regulated?
The determination of left/right symmetry is regulated by a combination of mechanical and biochemical signals. Nodal flow generated by motile cilia is sensed by immotile cilia, leading to calcium signaling that activates asymmetric gene expression. Planar cell polarity pathways coordinate cell orientation and tissue-level asymmetry. The Nodal-Lefty-Pitx2 cascade is subject to feedback inhibition by Lefty, which ensures the correct spatial and temporal restriction of Nodal activity. Additionally, KIF3 motor proteins regulate cilia assembly and function, indirectly controlling nodal flow.
determination of left/right symmetry and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| Nodal | Heterotaxy, congenital heart defects | Knockout mouse, zebrafish mutant |
| Lefty | Heterotaxy, left-right patterning defects | Knockout mouse, overexpression |
| Zic3 | Heterotaxy, situs inversus | Knockout mouse, patient-derived iPSCs |
| Dnah5 | Primary ciliary dyskinesia, situs inversus | Knockout mouse, zebrafish |
| KIF3 | Ciliopathy, left-right asymmetry defects | Conditional knockout mouse |
Heterotaxy and situs inversus
Disruption of left-right symmetry determination leads to heterotaxy, a condition where internal organs are arranged abnormally across the left-right axis, or situs inversus, where organs are mirrored. Mutations in genes such as Nodal, Lefty, and Zic3 are associated with these disorders. Ciliary defects, as seen in primary ciliary dyskinesia, frequently cause situs inversus due to impaired nodal flow.
Congenital heart defects
Abnormal left-right patterning is a major cause of congenital heart defects, as the heart is one of the first organs to exhibit asymmetry. Defects in Nodal signaling or cilia function can lead to malformations such as transposition of the great arteries and ventricular septal defects.
Ciliopathies
Ciliopathies, including Bardet-Biedl syndrome and primary ciliary dyskinesia, often present with left-right asymmetry defects because cilia are essential for nodal flow and sensing. Mutations in KIF3 or intraflagellar transport proteins disrupt cilia assembly and cause left-right patterning abnormalities.
From determination of left/right symmetry-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does gene X regulate left-right asymmetry? | Knockout (KO) in zebrafish or mouse |
| Does a specific point mutation in gene X cause heterotaxy? | Point mutation knock-in in mouse |
| How does gene X affect nodal flow? | Tagged knock-in with fluorescent reporter |
| Can overexpression of gene X rescue asymmetry defects? | Overexpression in zebrafish embryos |
| What is the role of gene X in cilia assembly? | Knockout in cell culture followed by imaging |
| Does gene X interact with Nodal signaling? | Knock-in of epitope tag for co-IP |
How to Study the determination of left/right symmetry Process
| Method | What It Measures | Typical Application |
|---|---|---|
| High-speed video microscopy | Cilia beating and fluid flow | Analysis of nodal flow |
| Particle image velocimetry | Flow direction and velocity | Quantification of leftward flow |
| Calcium imaging | Intracellular calcium dynamics | Detection of asymmetric calcium signals |
| In situ hybridization | mRNA localization | Visualization of asymmetric gene expression |
| RNA-seq | Global transcriptome | Identification of left-right asymmetric genes |
| CRISPR/Cas9 knockout | Gene function loss | Testing requirement for left-right asymmetry |
| Immunofluorescence | Protein localization | Cilia and planar cell polarity protein distribution |
Imaging of cilia and nodal flow
High-speed video microscopy and particle image velocimetry are used to visualize motile cilia at the embryonic node and quantify fluid flow direction and speed. Fluorescent labeling of cilia components allows assessment of cilia morphology and positioning.
Calcium imaging
Genetically encoded calcium indicators (e.g., GCaMP) enable real-time monitoring of asymmetric calcium signals at the node and in surrounding tissues, revealing how flow sensing is translated into biochemical asymmetry.
Gene expression analysis
In situ hybridization and quantitative RT-PCR are used to detect asymmetric expression of Nodal, Lefty, and Pitx2 in embryos. RNA-seq can provide a global view of left-right asymmetric transcription.
Genetic manipulation in model organisms
CRISPR/Cas9-mediated knockout, knock-in, and overexpression in zebrafish, Xenopus, and mouse are standard approaches to test gene function in left-right patterning. Conditional alleles allow tissue-specific analysis.
How CRISPR Can Be Used to Study GO:0007368 determination of left/right symmetry
Knockout
CRISPR/Cas9 knockout of candidate genes in zebrafish or mouse embryos is used to test whether they are required for left-right symmetry determination. For example, knockout of Nodal or KIF3 results in abnormal left-right patterning.
Point Mutation
Point mutations identified in patients with heterotaxy can be introduced into model organisms using CRISPR/Cas9 to assess their pathogenicity and effects on left-right asymmetry.
Knock-in
Knock-in of fluorescent tags or epitope tags into endogenous loci allows visualization and biochemical analysis of proteins involved in left-right determination, such as Nodal or Pkd2.
Overexpression
CRISPR activation (CRISPRa) or transgenic overexpression can be used to test whether increased dosage of a gene disrupts left-right asymmetry, as seen with Nodal or Lefty.
How EDITGENE Supports determination of left/right symmetry Research
Researchers studying determination of left/right symmetry-related genes often need to determine whether a candidate gene is causally involved in asymmetry or merely correlated with it. EDITGENE provides a comprehensive suite of CRISPR-based services to enable such functional studies in relevant model systems.
Contact EDITGENE today to design your custom CRISPR model for determination of left/right symmetry research.
Frequently Asked Questions About determination of left/right symmetry
What is GO:0007368?
GO:0007368 is the Gene Ontology term for determination of left/right symmetry, the biological process that establishes an organism's body plan with respect to the left and right halves.
What genes are involved in determination of left/right symmetry?
Key genes include Nodal, Lefty, Pitx2, KIF3, and various cilia-related genes such as Dnah5 and Ift88.
How is left-right symmetry broken in embryos?
In vertebrates, motile cilia at the embryonic node generate a leftward fluid flow that is sensed by immotile cilia, triggering asymmetric calcium signaling and gene expression.
What diseases are associated with defects in left-right symmetry?
Defects cause heterotaxy, situs inversus, congenital heart defects, and ciliopathies such as primary ciliary dyskinesia.
What is the role of cilia in left-right determination?
Motile cilia generate nodal flow, while immotile cilia sense the flow direction, initiating the asymmetric signaling cascade.
How can CRISPR be used to study left-right symmetry?
CRISPR knockout, knock-in, and point mutation models allow functional testing of candidate genes in zebrafish, mouse, and cell culture.
What is the Nodal signaling pathway?
Nodal is a left-sided morphogen that induces Lefty and Pitx2, establishing left-sided identity in developing organs.
What is the role of KIF3 in left-right asymmetry?
KIF3 is a molecular motor required for cilia assembly and nodal flow, and its disruption impairs left-right determination.
Which model organisms are used to study left-right asymmetry?
Zebrafish, Xenopus, and mouse are commonly used due to their accessible embryos and conserved left-right pathways.
What methods are used to study left-right symmetry?
Methods include high-speed video microscopy, calcium imaging, in situ hybridization, RNA-seq, and CRISPR-based genetic manipulation.
Conclusion
Determination of left/right symmetry (GO:0007368) is a fundamental developmental process that relies on the coordinated action of cilia, calcium signaling, planar cell polarity, and asymmetric gene expression. Disruption of this process leads to clinically significant disorders such as heterotaxy and congenital heart defects. Continued research using CRISPR models and advanced imaging will further elucidate the mechanisms and identify therapeutic targets.
References
- 1. Shi DL. 2024. Breaking Left-Right Symmetry by the Interplay of Planar Cell Polarity, Calcium Signaling and Cilia.. Cells 13(24) PMID: 39768206
- 2. Katoh TA. 2024. Function of nodal cilia in left-right determination: Mechanical regulation in initiation of symmetry breaking.. Biophys Physicobiol 21(3):e210018 PMID: 39802743
- 3. Naganathan SR et al.. 2022. Left-right symmetry of zebrafish embryos requires somite surface tension.. Nature 605(7910):516-521 PMID: 35477753
- 4. Katoh TA et al.. 2023. Immotile cilia mechanically sense the direction of fluid flow for left-right determination.. Science 379(6627):66-71 PMID: 36603091
- 6. Ibañes M et al.. 2009. Left-right axis determination.. Wiley Interdiscip Rev Syst Biol Med 1(2):210-219 PMID: 20835993
- 7. Hirokawa N et al.. 2009. Left-right determination: involvement of molecular motor KIF3, cilia, and nodal flow.. Cold Spring Harb Perspect Biol 1(1):a000802 PMID: 20066075
- 8. Mercola M et al.. 2001. Left-right asymmetry determination in vertebrates.. Annu Rev Cell Dev Biol 17:779-805 PMID: 11687504
