# DBT JRF 2022 — Question 139

Exam: DBT JRF 2022 · Section: B · Topic: Animal Biotechnology › Animal Cloning - Enucleation Protocol · Difficulty: Medium

## Question

In animal cloning protocol, while performing enucleation, which chemical is used for relaxing the cellular cytoskeleton?

## Options

- **A.** Phytohaemagglutinin
- **B.** Cytochalasin B
- **C.** Pronase
- **D.** Heparin

## Answer

Option B

## Explanation

Cytochalasin B in enucleation for somatic cell nuclear transfer: In animal cloning by somatic cell nuclear transfer (SCNT), the recipient oocyte must first be ENUCLEATED (nucleus removed): Procedure: 1. Mature metaphase II oocyte is treated with CYTOCHALASIN B. 2. Cytochalasin B: a fungal metabolite that disrupts ACTIN FILAMENT polymerisation (binds barbed end of actin filaments, prevents polymerisation). 3. This disruption RELAXES the cytoskeleton and cell membrane → makes the oocyte soft and permeable. 4. The zona pellucida is pierced with a micropipette → the metaphase chromosomes and spindle complex can be gently aspirated. Alternatively, UV irradiation can be used to destroy the DNA (chemical-free enucleation). Other agents: • Phytohaemagglutinin (PHA): T cell mitogen; not for enucleation. • Colchicine/taxol: microtubule inhibitors, different target. • Pronase: enzyme to remove zona pellucida, not for enucleation per se. Answer: Cytochalasin B disrupts actin filaments, relaxing the oocyte cytoskeleton to allow gentle nucleus removal.

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