Question

Some lower vertebrates such as fish and amphibians can control their color by regulating specialized pigment cells called melanophores. These cells contain small, pigmented organelles, termed melanosomes, that can be dispersed throughout the cell, making the cell darker, or aggregated in the center of the cell to make the cell lighter. You purify the melanosomes from melanophores that have either aggregated or dispersed melanosomes and find that: 1. aggregated melanosomes co-purify with dynein; 2. dispersed melanosomes co-purify with kinesin. Given this set of data, propose a mechanism for how the aggregation and dispersal of melanosomes occur.

Answer 1

The aggregation and dispersal of melanosomes within melanophores, influencing skin color, may be driven by the opposite directional movement of melanosomes by the molecular motors dynein and kinesin along microtubules.

Step-by-step explanation:

Among lower vertebrates such as fish and amphibians, the control of skin color involves specialized pigment cells known as melanophores. These cells contain melanosomes which can alter the overall coloring by their distribution within the cell. When melanosomes aggregate within melanophores, the cell appears lighter; while a dispersion of melanosomes makes the cell appear darker. The provided data shows that aggregated melanosomes co-purify with dynein, whereas dispersed melanosomes co-purify with kinesin. Since dynein and kinesin are molecular motors that transport cargo along microtubules in opposite directions, a proposed mechanism is that dynein drives aggregation by moving melanosomes towards the cell center, and kinesin disperses them by carrying them towards the cell periphery.