Question

Why do humans have different skin color? Does UVR play a significant role in this and what is the history of pigmentation in reference to our ancestors?

Answer 1

• Skin pigmentation is due to melanin pigment.
• Melanin pigments are formed in melanocytes within melanosomes.
• The pH in the melanosome controls the melanin formation.
• More acidic pH relates to lesser melanin formation.
• Thus, pH in melanosomes of darker-skinned people are less acidic than lighter-skinned people.
• Melanocyte formation is dependent of secretory pathway proteins.
• Two major transporters are OCA2/P and SLC45A2.
• OCA2/P acts as anion transporter and may supply protons which act as pH regulator.
• pH regulation is also determined by soluble Adenylyl cyclase (sAC), that produce cAMP.
• Inhibition of sAC increases pH.
• Enzyme Tyrosinase (Tyr) acts as the rate limiting enzyme in melanin synthesis.
• The tyrosinase family enzymes- Oxygenase Tyrosinase- related protein-1 (Tyrp-1) and dopachrome tautomerase (DCT or Tyrp-2).
• Tyr, Tyrp-1, Tyr-2 interact with each other to control melanocyte production and is more active in basic pH.
• Thus, decrease in pH of acidic pH in turn inhibit Tyrosinase, and causing less melanocyte maturation and less melanin formation.
• The evolution of dark skin is considered as a natural selection process to prevent folate depletion and prevent DNA damage to some extent.
• UV radiation exposure to skin causes damage to DNA and breakdown of folate.
• Melanin reduces folate breakdown.