# DBT JRF 2022 — Question 137

Exam: DBT JRF 2022 · Section: B · Topic: Cell Biology › Metazoan Development & Cell Differentiation · Difficulty: Medium

## Question

Choose the correct statement in respect to metazoan development:

## Options

- **A.** Delta is a cell surface protein while Notch is an intracellular protein.
- **B.** Notch is a cell surface protein while Delta is an intracellular protein.
- **C.** Delta and Notch are not present on the same cell.
- **D.** Notch and Delta both are cell surface proteins present on the same precursor cell.

## Answer

Option D

## Explanation

Notch-Delta signalling in lateral inhibition: In Notch signalling during metazoan development: • Notch: a single-pass transmembrane RECEPTOR (type I) — expressed on the surface of the receiving cell. • Delta (and Serrate/Jagged): transmembrane LIGANDS — expressed on the surface of the signal-sending cell. Lateral inhibition mechanism: 1. In a field of equivalent precursor cells, all initially express BOTH Notch and Delta. 2. Random fluctuations: one cell slightly upregulates Delta → activates Notch in adjacent cells. 3. Notch activation → represses Delta in that cell (via Hairy/Enhancer of split). 4. Through feedback: one cell becomes 'Delta-high/Notch-low' (neuronal/primary fate); its neighbours become 'Notch-high/Delta-low' (non-neuronal/secondary fate). Key point: Notch and Delta CAN be on the SAME precursor cell, but after fate specification they become DIFFERENTIALLY expressed. Answer: Both Notch (receptor) and Delta (ligand) are cell surface proteins on the same precursor cell; lateral inhibition drives differential expression during fate determination.

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