A researcher studies a toxin that specifically targets the motor protein kinesin. Which cellular component would be absent on histology?

• A. Secretory vesicles in nerve terminals
• B. Microvilli in intestinal epithelial cells
• C. Desmosomes in epithelial lining cells
• D. Nissl substance in pyramidal neurons

Answer: (A)

Kinesin moves cargo along microtubules from the neuron’s cell body toward the axon terminal, delivering membrane-bound vesicles and organelles to the presynaptic site. If a toxin specifically inhibits kinesin, these secretory vesicles wouldn’t reach the nerve terminal, so histology would show an absence of secretory vesicles in the presynaptic terminal.

Other structures aren’t driven by kinesin-dependent anterograde transport in the same way. Microvilli rely on actin filaments, not axonal transport along microtubules. Desmosomes are cell–cell junctions built from cadherins and intermediate filaments, not vesicle traffic along axons. Nissl substance represents rough endoplasmic reticulum and ribosomes in the neuron’s soma, not vesicles delivered to axon terminals.