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Microcell Fusion Technique – Detailed Notes


Microcell Fusion Technique – Detailed Notes


1. Definition 

Microcell fusion is a technique in which microcells containing isolated chromosomes or chromosomal fragments from a donor cell are fused with recipient cells.
It is used for chromosome transfer, gene mapping, and creating hybrid cell lines.
Also called microcell-mediated chromosome transfer (MMCT).
2. Principle
Donor cells containing the chromosome of interest are treated with colchicine to induce micronuclei formation.
These micronuclei are isolated as microcells (small cytoplasmic vesicles containing one or a few chromosomes).
Microcells are fused with recipient cells using fusion agents such as PEG or Sendai virus.
The chromosome from the donor is incorporated into the recipient cell, creating a stable hybrid.
Key Concept:
Microcell fusion allows transfer of specific chromosomes from donor to recipient without introducing the whole genome.


3. Steps in Microcell Fusion Technique


Step 1: Preparation of Donor Cells

Donor cells contain the chromosome(s) of interest, often labeled with selectable markers.
Cells are treated with colchicine, which disrupts mitotic spindle formation.
This produces micronuclei, small nuclear fragments containing single chromosomes.

Step 2: Isolation of Microcells

Micronucleated donor cells are treated with cytochalasin B, which inhibits cytoplasmic division.
Cells are centrifuged through a Percoll density gradient to isolate microcells.
Microcells are small vesicles (~2–5 µm) containing single or few chromosomes.

Step 3: Fusion with Recipient Cells


Microcells are fused with recipient cells using:
A. PEG-Mediated Fusion
Polyethylene glycol induces membrane fusion between microcells and recipient cells.
B. Virus-Mediated Fusion
Inactivated Sendai virus is used to facilitate fusion of microcell membranes with recipient cells.

Step 4: Selection of Hybrid Cells

Recipient cells receiving the donor chromosome are selected using selectable markers (e.g., antibiotic resistance, reporter genes).
Hybrid cells are then expanded in culture.

Step 5: Analysis of Hybrid Cells

Hybrid cells are analyzed for chromosome retention, gene expression, and functional traits.
Techniques include:
Karyotyping
Fluorescent in situ hybridization (FISH)
PCR or molecular markers

4. Factors Affecting Microcell Fusion

Donor cell preparation – Colchicine concentration and treatment duration
Recipient cell type – Must be compatible and capable of growth
Fusion method – PEG concentration, viral activity, incubation time
Selection strategy – Choice of selectable markers
Microcell viability – Critical for successful fusion
5. Applications of Microcell Fusion Technique

5.1 Gene Mapping


Transfer individual chromosomes to recipient cells for mapping gene loci.
Example: Transfer human chromosome 21 into hamster cells for mapping Down syndrome-related genes.

5.2 Functional Genomics

Study gene function by isolating and expressing single donor chromosomes in a new cellular environment.

5.3 Production of Hybrid Cell Lines

Generate somatic cell hybrids with specific chromosomes for research.
Example: Human-mouse hybrid cell lines for gene expression studies.

5.4 Disease Research


Study genetic diseases by transferring mutant chromosomes into recipient cells.
Example: Identify genes responsible for metabolic disorders.

5.5 Chromosome Engineering

Combine specific donor chromosomes with recipient cells for gene transfer and therapeutic research.

6. Advantages of Microcell Fusion


Transfer specific chromosomes or chromosomal fragments
Bypasses sexual or species barriers
Produces stable hybrid cell lines
Useful in gene mapping and functional genomics
Can introduce large DNA fragments that are difficult with plasmids or viral vectors

7. Limitations
Technically demanding and labor-intensive
Low efficiency of microcell fusion
Requires careful donor cell preparation
Hybrid cells may lose donor chromosomes over time
Requires selectable markers for identification

8. Examples
Donor Chromosome
Recipient Cell
Purpose
Human chromosome 21
Chinese hamster ovary (CHO) cells
Gene mapping, Down syndrome studies
Human chromosome 7
Mouse cells
Functional genomics, disease gene identification
Specific donor chromosome
Fibroblast cells
Production of hybrid cell lines for research

Advantages
Transfer specific chromosomes, bypass sexual barriers, stable hybrids.

Limitations
Technically demanding, low efficiency, requires selection



Microcell Fusion Technique – 50 MCQs


Microcell fusion is used to:
a) Fuse plant protoplasts
b) Transfer donor chromosomes to recipient cells ✅
c) Fuse viral particles
d) Introduce RNA only
Microcell fusion is also called:
a) Somatic hybridization
b) Microcell-mediated chromosome transfer (MMCT) ✅
c) DNA-mediated transformation
d) Lipofection
Microcells are:
a) Whole donor cells
b) Cytoplasmic vesicles containing one or few chromosomes ✅
c) Viral particles
d) Plasmids
Donor cells are treated with which chemical to induce micronuclei?
a) PEG
b) Colchicine ✅
c) Cytochalasin B
d) Cellulase
Cytochalasin B is used to:
a) Induce fusion
b) Prevent cytoplasmic division and isolate microcells ✅
c) Digest cell walls
d) Label chromosomes
Microcells contain:
a) Entire genome
b) One or few chromosomes ✅
c) Only RNA
d) Only cytoplasm
Fusion of microcells with recipient cells can be done by:
a) PEG-mediated fusion ✅
b) Electroporation
c) Lipofection
d) Calcium phosphate precipitation
Virus-mediated fusion uses:
a) Active viruses
b) Inactivated Sendai virus ✅
c) Retrovirus
d) Adenovirus
Microcell fusion is primarily applied in:
a) Plant protoplast fusion
b) Chromosome transfer and hybrid cell production ✅
c) Bacterial transformation
d) RNA interference
Selectable markers are important in microcell fusion to:
a) Induce fusion
b) Identify successful hybrid cells ✅
c) Digest cell walls
d) Label chromosomes
Hybrid cells generated by microcell fusion contain:
a) Only recipient chromosomes
b) Donor chromosome(s) plus recipient genome ✅
c) Only donor chromosomes
d) Only cytoplasm
Donor cell chromosomes may be labeled with:
a) Fluorescent markers ✅
b) PEG
c) Colchicine
d) Lipid vesicles
Density gradient centrifugation is used to:
a) Fuse microcells
b) Isolate microcells ✅
c) Select hybrid cells
d) Digest cell walls
PEG (Polyethylene Glycol) in microcell fusion acts by:
a) Digesting cell walls
b) Destabilizing membranes to allow fusion ✅
c) Selecting hybrid cells
d) Labeling chromosomes
Which of the following is a key advantage of microcell fusion?
a) Transfers only RNA
b) Transfers specific donor chromosomes ✅
c) Works without donor cell preparation
d) Requires no selection
Microcell fusion bypasses:
a) Sexual reproductive barriers ✅
b) Cell culture
c) DNA transfer
d) Protein synthesis
Donor cells must be treated with colchicine for:
a) 1–2 minutes
b) Several hours to induce micronuclei formation ✅
c) Only to label chromosomes
d) To digest the cytoplasm
Microcells are typically:
a) 20–50 µm
b) 2–5 µm ✅
c) 10–15 µm
d) 50–100 µm
Cytochalasin B inhibits:
a) DNA replication
b) Cytokinesis ✅
c) Chromosome segregation
d) Nuclear division
Hybrid cell lines created by microcell fusion are useful for:
a) Gene mapping ✅
b) Functional genomics ✅
c) Disease research ✅
d) All of the above ✅
Microcell fusion efficiency depends on:
a) Donor cell preparation ✅
b) Recipient cell type ✅
c) Fusion method and incubation conditions ✅
d) All of the above ✅
Hybrid cells can be analyzed using:
a) Karyotyping ✅
b) FISH (Fluorescent in situ hybridization) ✅
c) PCR ✅
d) All of the above ✅
Microcell fusion can transfer:
a) Nuclear chromosomes ✅
b) Cytoplasmic organelles
c) Only DNA plasmids
d) Only RNA
Donor chromosomes may carry:
a) Selectable markers ✅
b) Antibiotic resistance genes ✅
c) Reporter genes ✅
d) All of the above ✅
Microcell fusion is technically:
a) Simple and fast
b) Labor-intensive and demanding ✅
c) Only for plants
d) Only for bacteria
Hybrid cells are selected based on:
a) Morphology
b) Marker gene expression ✅
c) Chromosome number
d) Cell size
Microcell fusion can be applied to study:
a) Gene function ✅
b) Disease mechanisms ✅
c) Chromosome mapping ✅
d) All of the above ✅
Donor cells for microcell fusion are often:
a) Tumor cells ✅
b) Plant cells
c) Bacterial cells
d) Viral particles
Which step is critical for microcell viability?
a) Colchicine treatment duration ✅
b) Fusion method
c) Selectable marker choice
d) PCR analysis
Hybrid cells may lose donor chromosomes over time due to:
a) Culture instability ✅
b) Fusion method
c) PEG concentration
d) Colchicine treatment
Microcell fusion can transfer:
a) Single chromosomes ✅
b) Multiple chromosomes ✅
c) Entire genome
d) Both a & b ✅
Microcell fusion is used in human genetics to:
a) Study Down syndrome genes ✅
b) Study plant traits
c) Bacterial cloning
d) Viral replication
Hybrid cells can express genes from:
a) Donor chromosomes ✅
b) Recipient chromosomes ✅
c) Both donor and recipient ✅
d) None
A limitation of microcell fusion is:
a) High efficiency
b) Requires careful donor cell preparation ✅
c) Works without selection
d) Can transfer RNA only
Sendai virus in microcell fusion functions as:
a) Selectable marker
b) Fusion agent ✅
c) Donor chromosome carrier
d) Cytoplasmic stabilizer
Hybrid cells are maintained in culture using:
a) Selective medium ✅
b) PEG only
c) Colchicine only
d) Viral infection
Applications of microcell fusion in cancer research include:
a) Mapping oncogenes ✅
b) Generating hybrid cell lines ✅
c) Functional genomics ✅
d) All of the above ✅
Microcell fusion can transfer which types of chromosomes?
a) Autosomes ✅
b) Sex chromosomes ✅
c) Fragmented chromosomes ✅
d) All of the above ✅
Hybrid cells can be used to study:
a) Drug resistance ✅
b) Gene expression ✅
c) Cytogenetic abnormalities ✅
d) All of the above ✅
Microcell fusion differs from protoplast fusion because:
a) It transfers whole cells
b) It transfers only chromosomes, not whole cells ✅
c) It uses plant tissues only
d) It uses viral vectors
Key chemical for micronuclei induction is:
a) PEG
b) Colchicine ✅
c) Cytochalasin B
d) Calcium chloride
PEG is used in microcell fusion to:
a) Digest cell walls
b) Promote membrane fusion ✅
c) Select hybrid cells
d) Label chromosomes
Donor chromosomes may be marked with:
a) Fluorescent probes ✅
b) Antibiotic resistance genes ✅
c) Reporter genes ✅
d) All of the above ✅
Density gradient centrifugation isolates:
a) Donor chromosomes
b) Microcells ✅
c) Recipient nuclei
d) Viral particles
Microcell fusion can produce stable hybrids for:
a) Long-term gene mapping ✅
b) Temporary expression
c) Only protoplast studies
d) Only viral vectors
Hybrid cells can retain donor chromosomes depending on:
a) Culture conditions ✅
b) Donor chromosome type ✅
c) Selective pressure ✅
d) All of the above ✅
Microcell fusion is used in mapping which human chromosome associated with Down syndrome?
a) Chromosome 21 ✅
b) Chromosome 7
c) Chromosome 1
d) Chromosome X
Hybrid cells from microcell fusion are analyzed by:
a) Karyotyping ✅
b) PCR ✅
c) FISH ✅
d) All of the above ✅
A major advantage of microcell fusion is:
a) Transfers whole donor genome
b) Transfers specific chromosomes ✅
c) No selection required
d) Works only in plants
Overall, microcell fusion is important in:
a) Gene mapping ✅
b) Functional genomics ✅
c) Disease research ✅
d) All of the above ✅


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