pigmentgranula

Pigmentgranula, or pigment granules, are small organelles that contain pigmented compounds within cells. They participate in producing and organizing color, and in some contexts provide protection from ultraviolet radiation. The best-characterized pigment granula in animals are melanosomes, specialized organelles formed in melanocytes of the skin, hair follicles, and ocular tissues. In other cell types, pigment granules may carry carotenoids or other pigments, contributing to local coloration.

Melanosomes are membrane-bound structures that synthesize and store melanin. They mature in a series of stages (I to IV): early premelanosomes form a matrix, then elongated fibrils guide pigment deposition, and finally mature melanosomes become densely pigmented. The enzyme tyrosinase drives melanin synthesis inside these organelles.

After maturation, melanosomes are transported within melanocytes and transferred to neighboring keratinocytes, contributing to skin and hair color and to photoprotection by absorbing ultraviolet light.

Variation in pigment granula size, number, and distribution underlies natural color diversity among individuals and species and can be subject to genetic regulation as well as environmental influences.

Defects in pigment granula formation or transport can lead to pigmentary disorders, such as albinism, where melanin production or distribution is reduced or absent, or other hypopigmented conditions. In addition to melanosomes, pigment granula may reflect broader cellular strategies for pigment storage and distribution across tissues, illustrating the role of these organelles in physiology and appearance.