I. The ligand and the receptor engage in reciprocal signaling
II. Both the ligand and the receptor are membrane associated proteins
III. The ligand gets proteolytically cleaved after binding to the receptor
(A) I only
(B) II only
(C) III only
(D) I, II and III
Juxtacrine signaling involves direct cell-cell contact through membrane-associated ligand-receptor pairs, enabling precise developmental patterning without diffusible signals.
Correct Answer
(B) II only
Statement Analysis
I. The ligand and the receptor engage in reciprocal signaling
FALSE. While bidirectional signaling occurs in some cases (e.g., Notch-Delta where ligand cell also signals), it’s not defining for juxtacrine signaling. Core feature is direct contact, not mandatory reciprocity. Classic examples like Ephrin-Eph are unidirectional.
II. Both the ligand and the receptor are membrane associated proteins
TRUE. This defines juxtacrine signaling—both signaling molecules remain anchored to their respective cell membranes, requiring physical contact. Examples: Notch (receptor) and Delta (ligand), both transmembrane proteins.
III. The ligand gets proteolytically cleaved after binding to the receptor
FALSE. Cleavage occurs in specific pathways (Notch: ligand binding triggers receptor cleavage by γ-secretase), but ligands themselves typically remain membrane-bound. Proteolytic release defines paracrine signaling, not juxtacrine.
| Statement |
True for Juxtracrine? |
Key Examples |
| I. Reciprocal signaling |
No |
Optional (Notch bidirectional) |
| II. Membrane-bound |
Yes |
Notch-Delta, Ephrin-Eph |
| III. Ligand cleavage |
No |
Receptor cleavage only |
Core Mechanism
Juxtacrine = “juxtaposed” cells. Membrane-tethered ligands (Delta, Ephrins) engage adjacent cell receptors (Notch, Eph), triggering intracellular cascades without soluble mediators. Critical for embryonic patterning, synapse formation.
Developmental biologists note: Distinguish from paracrine (soluble ligands) where only receptors are membrane-bound.
SEO-Friendly Article Context
Juxtacrine signaling requires membrane associated ligand-receptor pairs for direct cell communication, making II the defining true statement essential for CSIR-NET/GATE cell signaling questions.
