Model for the molecular action of the melanophore-differentiating and melanogenic genes within melanophores.

<p>Inside melanosomes, the master regulator of melanogenesis, <i>mitf</i>, can regulate the action of <i>tyr</i>, <i>trp2</i> and <i>trp1,</i> coding for the main enzymes responsible for the synthesis of melanin. Besides, the action of <i>Slc24a5,</i> which is the calcium melanosomal transporter, is crucial for proper melanin synthesis. <i>Pax3</i> is a key upstream transcription factor in the cascade that can promote or inhibit melanogenesis through transcriptional regulation <i>mitf</i> and <i>cKit</i>, the latter being necessary for melanophore differentiation and responsible for the activation of <i>tyr</i>. <i>Pax3</i> can also modulate the expression of the two other melanogenic enzymes <i>trp1</i> and <i>trp2</i>. <i>Mc1r</i>, located to the melanophore membrane, is activated by <i>α-MSH</i> and promotes the activation of <i>tyr</i>. <i>Asip</i> can inhibit the action of <i>mc1r</i> and <i>slc24a5</i>. <i>Hsp70</i> has been shown to be a negative regulator of <i>casp3</i> and the latter a negative regulator of <i>mitf</i>. <i>α-MSH, α</i>-melanocyte-stimulating hormone; <i>asip, agouti signaling protein</i>; <i>casp3, caspase 3</i>; <i>cKit, mast/stem cell growth factor receptor Kit; dtc/trp2</i>, <i>L-dopachrome tautomerase; mc1r, melanocyte-stimulating hormone 1 receptor</i>; <i>mitf</i>, <i>microphtalmia-associated transcription factor</i>; <i>pax3</i>, <i>paired box protein Pax-3; sl, somatolactin</i>; <i>slc24a5, sodium/potassium/calcium exchanger</i>; <i>tyr, tyrosinase</i>; <i>trp1, tyrosinase-related protein 1</i>.