Properties and state of particulate tyrosinase of xanthic goldfish

Deficiency of the gene B impairs differentiation of melanophores in the medaka fish, Oryzias latipes: fine structure studies

In an orange-colored variant of the medaka fish, Oryzias latipes, which is homozygous for b allele, the melanophores represent a tissue-specific differentiation, manifesting an amelanotic appearance in the skin, an incomplete melanogenesis in the choroid and the peritoneum, and mosaic phenotype-like melano-iridophores in the peritoneum. In a wild-type strain of this species carrying the B gene, all melanophores are terminally differentiated irrespective of the tissues in which they are located. This indicates that the deficiency of B gene impairs the differentiation of melanophores in the medaka. Electron microscopy disclosed that the deficiency of B gene causes deterioration of melanogenesis to occur inside the melanosomes and that the manner of deterioration in the melanophores in the skin, the choroid and the peritoneum is different. The ubiquitous occurrence of reflecting platelet-laden melanophores in the peritoneum of this variant and the total absence of a mosaicism in pigment cells of the wild-type strain indicate that the deficiency of B gene predestines melanoblasts distributed in this tissue to an ambiguous state with regard to their differentiation. Little difference is observed between melanosomes maturation in pigment epithelial cells of the orange-colored variant and the wild-type strain, indicating an innocent role of the B gene in their differentiation.

A study on melanogenesis and catecholamine biosynthesis during Bufo bufo development

Tyrosinase and L-DOPA decarboxylase activities have been investigated during Bufo bufo development since catecholamines and melanin are formed from common substrates in homologous cells. Catecholamines first appear at stage 13 (neural plate), but tyrosinase, at a very low level, and L-DOPA decarboxylase are present throughout all of prior development. Hence, L-DOPA decarboxylase activity is not likely to be correlated with the control of catecholamine synthesis, although at stage 17 it is mainly localized in the nonneural part of the embryo. The distribution of young melanosomes and L-DOPA decarboxylase suggest a separation between melanogenesis and catecholamine synthesis.

Inhibition of tyrosinase by indole compounds and reaction products. Protection by albumin

Tyrosinase activity decreases as the reaction proceeds and is inhibited by L-3,4-dihydroxyphenylalanine oxidation products. Indole and tryptophan inhibit tyrosinase reaction and bovine albumin protects against end-product(s) inhibition or inactivation. Since the same tyrosinase reaction products are indole compounds and some authors reported the binding of indole derivatives with albumin, it is here suggested that indole intermediates of melanin synthesis inhibit or inactivate tyrosinase.

Genetic control of cell differentiation in platyfish-swordtail melanomas

In certain fish hybrids, malignant transformation of pigment cells is due to the presence of a tumor gene (Tu), the action of which is controlled by several regulatory elements. Absence of these controlling genes causes rapid proliferation of the Tu-transformed cells and ultimately results in melanoma formation. One of these genes has been identified as a differentiation gene (Diff), since it seems to control the differentiation of the transformed pigment cells. Light and electron microscopy of Tu-transformed cells of fish differing in the dosage of Diff, and the determination of tyrosinase activity in homogenates of the respective tissues revealed that the degree of cellular differentiation depends on the dosage of Diff present in the genome. It is concluded that the gene Diff promotes the differentiation of malignant melanoma cells into benign melanophores.