The microphthalmia-associated transcription factor (Mitf) is a basic-helix-loop-helix-leucine zipper (bHLH-ZIP) transcription factor essential for the development and function of all melanin-producing pigment cells in vertebrates. To elucidate the evolutionary history of Mitf and the antiquity of its association with pigment cells, we have isolated and characterized HrMitf, a sole member of the Mitf-TFE bHLH-ZIP subfamily in the ascidian Halocynthia roretzi. Maternal HrMitf mRNA is detected in the fertilized egg and in the animal hemisphere from 4-cell stage through the gastrula stage. From the neurula through the early tailbud stage, HrMitf is preferentially expressed in the pigment-lineage cells that express the lineage-specific melanogenesis genes tyrosinase (HrTyr) and Tyrp. Overexpression of HrMitf induced ectopic expression of HrTyr enzyme activity in mesenchymal cells where the same enzyme activity was induced by overexpression of HrPax3/7, suggesting that a part(s) of the Pax3-Mitf-tyrosinase gene regulatory cascade seen in vertebrate melanocytes is operative during ascidian embryogenesis. We also show HrMitf and mouse Mitf-A, a Mitf isoform abundantly expressed in pigmented epithelial cells, share similar functional characteristics. These results suggest antiquity of the association of the Mitf-TFE subfamily with pigment cells and may support the idea that acquisition of multiple promoters (isoforms) by an ancestral Mitf gene has allowed the evolution of multiple pigment cell types.
Bibliographical noteFunding Information:
We are grateful to Drs N. Satoh and H. Nishida for helpful discussions, K. Ishida for technical advice on in situ hybridization. We wish to thank Drs Lamaire and Gurdon for allowing us to use the pBluescript RN3 and all members of the Marine Biological Station of Asamushi for supplying the living materials. This work was supported by a Grant-in-Aid from the Ministry of Education, Science and Culture, Japan and NIG Cooperative Research Programs (72-'96, 56-'97, 63-'98, 46-'99) to H.Y.
- Neural crest
- Pigment cells
- Transcription factor
ASJC Scopus subject areas
- Developmental Biology