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Microinjection Technique


Microinjection Technique

Definition:

Microinjection is a direct physical method for introducing foreign molecules (DNA, RNA, proteins, or organelles) into a single cell or nucleus using a fine glass micropipette under a microscope. It is widely used in transgenic animal production, functional genomics, and molecular biology studies.

1. Principle

Uses a micropipette to penetrate the cell membrane (or nuclear membrane) and inject molecules directly into the cytoplasm or nucleus.
Delivery is mechanical, not chemical or biological.
Allows precise control of the amount and location of the injected material.
Key idea: Microinjection bypasses natural barriers like the plasma membrane or nuclear envelope.

2. Materials Required


Microscope – usually an inverted or micromanipulation microscope.
Micromanipulator – to control the micropipette.
Microinjector – device to control pressure for injection.
Micropipettes – fine glass needles pulled to a tip of 0.5–5 µm diameter.
Cells/Embryos – zygotes, oocytes, somatic cells, or cultured cells.
DNA, RNA, or proteins – prepared at high purity and concentration.
Culture medium – to maintain cell viability post-injection.
3. Procedure / Steps

Step 1: Preparation of Cells
Cells or embryos are immobilized (sometimes with holding pipette).
For animal embryos, usually pronuclear stage zygotes are used.

Step 2: Micropipette Preparation

Glass capillary tubes are pulled using a micropipette puller.
The tip is sharpened and beveled for smooth penetration.

Step 3: Injection

Cell or embryo is held in position using a holding pipette.
Micropipette penetrates cytoplasm or pronucleus.
DNA, RNA, or protein is injected using controlled pressure.
Volume injected is usually 1–10% of cell volume to avoid damage.

Step 4: Post-Injection Handling

Injected cells are cultured in suitable medium.
Embryos may be transferred to host females (for animal transgenics).
Cells are monitored for expression of the injected gene or molecule.



5. Advantages

Precise delivery – exact amount and location.
Can introduce large DNA fragments (>100 kb).
Applicable to a wide variety of cells and embryos.
Produces transgenic animals with high efficiency in pronuclear injection.
Bypasses membrane barriers, unlike chemical methods.

6. Limitations

Technically demanding – requires skilled operator and equipment.
Low throughput – each cell is injected individually.
Risk of cell damage or death.
Not suitable for large-scale transformations.
Requires expensive instrumentation.

7. Applications

Production of transgenic animals
Pronuclear microinjection in mice, rats, and livestock.
Gene functional studies
Injection of mRNA or siRNA for gene knockdown or expression.
Protein expression
Microinjection of labeled proteins to study intracellular dynamics.
Genome editing
Delivery of CRISPR/Cas9 components into zygotes for gene editing.
Drug or organelle delivery
Study of intracellular processes by injecting mitochondria, dyes, or small molecules.


8. Notes / Tips


Cells must be healthy and properly immobilized.
Injected volume should be minimal to avoid lysis.
Micropipette tip size must match cell size.
Use sterile techniques to prevent contamination.
Microinjection is often combined with fluorescent markers to monitor successful delivery.



50 MCQs on Microinjection


Principle & Basics
Microinjection is a method to introduce molecules directly into:
A) Cell or nucleus
B) Only cytoplasm
C) Only membrane
D) Only mitochondria
Answer: A
Microinjection is classified as:
A) Chemical method
B) Physical method
C) Biological method
D) Vector-mediated method
Answer: B
Microinjection bypasses:
A) Membrane barriers
B) DNA replication
C) RNA transcription
D) Protein synthesis
Answer: A
The material injected can be:
A) DNA
B) RNA
C) Proteins
D) All of the above
Answer: D
Microinjection is commonly used in:
A) Plant protoplasts
B) Animal zygotes and cultured cells
C) Bacterial cells
D) Yeast cells
Answer: B
Equipment & Materials
The fine needle used is called:
A) Micropipette
B) Microcentrifuge tube
C) Capillary column
D) Microelectrode
Answer: A
Micropipette tip diameter is usually:
A) 0.5–5 µm
B) 10–50 µm
C) 50–100 µm
D) 100–200 µm
Answer: A
Micromanipulator is used to:
A) Pull DNA
B) Control micropipette movement
C) Measure pH
D) Centrifuge cells
Answer: B
Microinjector device is used to:
A) Control injection pressure and volume
B) Cut DNA
C) Visualize cells
D) Digest proteins
Answer: A
Cells must be immobilized using:
A) Centrifugation
B) Holding pipette or microholder
C) Heat shock
D) Osmotic buffer
Answer: B
Procedure / Steps
First step is:
A) DNA purification
B) Cell immobilization
C) Micropipette fabrication
D) Injection
Answer: B
DNA or RNA is injected into:
A) Cytoplasm or pronucleus
B) Cell wall only
C) Membrane exterior
D) Vacuoles only
Answer: A
Pronuclear injection is used mainly for:
A) Transgenic animal production
B) Protoplast fusion
C) Yeast mating
D) Viral infection
Answer: A
Microinjection requires:
A) Chemical fusogens
B) Skilled operator
C) Electroporation
D) Heat treatment
Answer: B
Volume injected is usually:
A) 50–100% of cell volume
B) 10–20% of cell volume
C) 1–10% of cell volume
D) 0.01% of cell volume
Answer: C
Micropipettes are made from:
A) Plastic tubes
B) Glass capillaries
C) Metal needles
D) Silicone tubes
Answer: B
Micropipette tips are:
A) Flattened
B) Sharpened and beveled
C) Rounded
D) Hollow with wide opening
Answer: B
Injected material is usually:
A) Sterile and highly purified
B) Crude cell lysate
C) Protease solution
D) Bacterial culture
Answer: A
After injection, cells are cultured in:
A) Osmotic buffer only
B) Suitable culture medium
C) Ethanol
D) Distilled water
Answer: B
Micromanipulation microscope is usually:
A) Inverted
B) Upright
C) Fluorescence only
D) Electron microscope
Answer: A
Applications
Microinjection is widely used in:
A) Transgenic animal production
B) Yeast fermentation
C) Bacterial cloning
D) Plant tissue culture
Answer: A
Injection of mRNA is used for:
A) Protein expression studies
B) DNA cloning
C) Cell wall digestion
D) Antibiotic production
Answer: A
CRISPR/Cas9 components are often delivered by:
A) Microinjection
B) PEG fusion
C) Agrobacterium
D) Viral transduction
Answer: A
Microinjection of pronuclei produces:
A) Stable transgenic lines
B) Temporary gene expression
C) RNA degradation
D) Protein denaturation
Answer: A
Injection of fluorescently labeled proteins is used to:
A) Study intracellular dynamics
B) Digest RNA
C) Lyse cells
D) Produce antibodies
Answer: A
Germline microinjection ensures:
A) Heritable gene transfer
B) Temporary expression
C) Membrane destabilization
D) Cell death
Answer: A
Microinjection can deliver:
A) DNA fragments >100 kb
B) Only small plasmids
C) Only RNA molecules
D) Only peptides
Answer: A
Cytoplasmic injection is preferred for:
A) RNA or protein expression
B) DNA integration
C) Pronuclear fusion
D) Cell wall regeneration
Answer: A
Microinjection allows study of:
A) Gene function at single-cell level
B) Population-level genetics only
C) Environmental effects
D) Bacterial replication
Answer: A
Microinjection is suitable for:
A) Both cultured cells and embryos
B) Only bacteria
C) Only plant leaves
D) Only fungi
Answer: A
Advantages
Microinjection provides:
A) Precise delivery
B) High throughput
C) Chemical-mediated transfer
D) Random DNA uptake
Answer: A
Large DNA fragments can be injected:
A) Yes
B) No
C) Only with chemical carriers
D) Only with viruses
Answer: A
Applicable to:
A) Wide variety of cells and embryos
B) Only protoplasts
C) Only bacterial cells
D) Only plant tissues
Answer: A
Bypasses:
A) Membrane and nuclear barriers
B) DNA synthesis
C) RNA transcription
D) Protein translation
Answer: A
High efficiency in pronuclear injection leads to:
A) Transgenic animals
B) Bacterial transformation
C) Temporary protein expression
D) Cell death
Answer: A
Limitations
Microinjection is:
A) Technically demanding
B) Simple
C) Cheap
D) High throughput
Answer: A
Each cell must be:
A) Injected individually
B) Treated in bulk
C) Heated
D) Frozen
Answer: A
Risk includes:
A) Cell damage or death
B) RNA transcription
C) Protein synthesis
D) Cell wall formation
Answer: A
Requires:
A) Expensive instrumentation
B) Only pipettes
C) Only chemicals
D) No equipment
Answer: A
Not suitable for:
A) Large-scale transformations
B) Single-cell studies
C) Functional analysis
D) Genome editing
Answer: A
Technical & Conceptual
Holding pipette is used to:
A) Immobilize the cell
B) Inject DNA
C) Monitor culture
D) Digest cell wall
Answer: A
Injected volume should be:
A) Minimal to avoid lysis
B) Maximal for efficiency
C) Equal to cell volume
D) Unimportant
Answer: A
Microinjection combined with fluorescent markers allows:
A) Monitoring successful delivery
B) DNA digestion
C) Protein denaturation
D) Membrane lysis
Answer: A
Micropipette is fabricated using:
A) Glass capillaries and a puller
B) Plastic tubes
C) Metal wires
D) Silicone tips
Answer: A
Pronuclear injection is mostly performed in:
A) Zygotes
B) Cultured bacteria
C) Plant leaves
D) Yeast cells
Answer: A
Microinjection is preferred when:
A) Precise, single-cell delivery is needed
B) Large-scale transformation is required
C) Viral vectors are available
D) Chemical methods work well
Answer: A
DNA integration occurs when injection is into:
A) Pronucleus
B) Cytoplasm only
C) Membrane
D) Mitochondria
Answer: A
Microinjection is a direct method because:
A) Material is physically introduced
B) It uses chemical carriers
C) It requires viruses
D) It relies on electroporation
Answer: A
Major application in research includes:
A) Transgenic animal creation
B) Plant tissue culture
C) Bacterial fermentation
D) Yeast mating
Answer: A
Main advantage of microinjection is:
A) High precision in single-cell delivery
B) Low cost
C) High throughput
D) Simple operation
Answer: A

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