"Pigment" - what is it, definition of the term
Pigment, the term designating biologically synthesized colored compounds, comprises organic molecules that selectively absorb light wavelengths, producing visible coloration in tissues such as fur, skin, and eyes of rodents like rats and mice; these substances—primarily melanin, carotenoids, and pteridines—are stored in specialized cells (e.g., melanocytes), and their concentration and distribution dictate the animal’s coat shade and pattern.
Detailed information
Rodent coloration derives from several classes of biological colorants. The primary dark pigment is melanin, a polymer of indole‑derived units that accumulates in hair shafts, skin epidermis, and ocular tissues. In laboratory strains, melanin concentration varies with mutations in the melanocortin‑1 receptor (MC1R) and the tyrosinase (TYR) gene, producing albino, agouti, and black phenotypes.
Carotenoid‑derived hue contributors appear in the diet and are deposited in fat deposits, liver, and the ventral fur of certain wild populations. These xanthophylls and carotenes impart yellow to orange tones and can be quantified by high‑performance liquid chromatography (HPLC).
Hemoglobin and its breakdown products, such as biliverdin, generate red and brown coloration in internal organs and, in some cases, the periorbital region. Spectrophotometric analysis of tissue extracts provides precise measurement of these chromophores.
Key aspects of rodent colorant biology include:
- Genetic regulation: allelic variants of MC1R, TYR, and the Agouti signaling protein (ASIP) determine melanin type and distribution.
- Developmental timing: melanocyte migration peaks during embryonic days 10–12, establishing the pattern of fur pigmentation.
- Environmental influence: exposure to ultraviolet light can increase melanin synthesis via up‑regulation of the enzyme tyrosinase‑related protein 1 (TYRP1).
Analytical techniques commonly employed:
- HPLC for carotenoid profiling.
- Mass spectrometry for melanin monomer identification.
- Reflectance spectrophotometry for in vivo fur color assessment.
Understanding these colorant systems supports research in genetics, toxicology, and visual physiology, as pigment alterations often serve as phenotypic markers for experimental manipulation.