melanosomi

Melanosomes are specialized organelles found in melanocytes, the pigment-producing cells in animals. These organelles are responsible for the synthesis, storage, and transport of melanin, the primary pigment responsible for skin, hair, and eye color. Melanosomes originate from the Golgi apparatus and undergo a maturation process, transitioning through several stages from Stage I (early, vesicular) to Stage IV (fully mature, electron-dense).

The primary function of melanosomes is to produce melanin through a complex biochemical pathway involving the enzyme tyrosinase. Once synthesized, melanin fills the melanosome. These mature melanosomes are then transferred from melanocytes to surrounding keratinocytes, the main cells of the epidermis. This transfer process, known as cytocrine secretion or pigment donation, is crucial for protecting the DNA in keratinocyte nuclei from damage caused by ultraviolet (UV) radiation. The melanin within melanosomes forms a cap-like structure over the nucleus, effectively shielding it.

The size, shape, and density of melanosomes, as well as the amount and type of melanin they contain (eumelanin for brown/black shades and pheomelanin for red/yellow shades), contribute to the diverse range of skin, hair, and eye colors observed across different individuals and species. Variations in melanosome production and distribution are influenced by genetic factors and environmental stimuli like sun exposure.