Cloning and functional analysis of ascidian Mitf in vivo: insights into the origin of vertebrate pigment cells.
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.
Yajima
Ichiro
I
Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan.
Endo
Kosuke
K
Sato
Shigeru
S
Toyoda
Reiko
R
Wada
Hiroshi
H
Shibahara
Shigeki
S
Numakunai
Takaharu
T
Ikeo
Kazuho
K
Gojobori
Takashi
T
Goding
Colin R
CR
Yamamoto
Hiroaki
H
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000201:enzymology / Q000378:metabolism; D019143:Evolution, Molecular; D005775:Gastrula / Q000166:cytology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor; D008957:Models, Genetic; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010860:Pigments, Biological; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D014561:Urochordata / Q000196:embryology* / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D014714:Vertebrates
D004268:DNA-Binding Proteins; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D010860:Pigments, Biological; D020033:Protein Isoforms; D012333:RNA, Messenger; D014157:Transcription Factors; D014442:Monophenol Monooxygenase