Fish Tumor Pigment Cells: Differentiation and Comparison to Their Normal Counterparts

The objectives of this paper are to describe 1) the development of new research systems for biochemical comparison of cellular traits between normal and tumorous pigment cells of fish origin, 2) the similarity and dissimilarity between these two categories of pigment cells with regard to growth, differentiation and pigment translocating activities and 3) the potentials of these tumorous pigment cells to manifest multiple differentiation. The development of research systems has been achieved by the establishment of 1) methods to obtain homogenous populations of viable, cultivatable xanthophores (erythrophores) and melanophores from goldfish skins, 2) permanent cell lines from goldfish erythrophoromas (tumors derived from erythrophores) and from Nibe croaker irido-melanophoromas (tumors composed of mixed populations of iridophore- and melanophore-like cells) and 3) procedures to induce differentiation in normal and tumorous stem cells (including the formation of pigments and ability to undergo pigment translocation in response to cAMP, to the neurotransmitter epinephrine and to the hormones ACTH and melatonin). Two kinds of tumorous pigment cell lines examined herein have the ability to form, in addition to various pigments, structures similar to dermal skeletons and lentoid bodies. These findings strongly suggest the possibility that these fish pigment cell tumors are neural crest stem cell tumors in nature.