Alternative promoter use in eye development: the complex role and regulation of the transcription factor MITF.
During vertebrate eye development, the transcription factor MITF plays central roles in neuroepithelial domain specification and differentiation of the retinal pigment epithelium. MITF is not a single protein but represents a family of isoforms generated from a common gene by alternative promoter/exon use. To address the question of the role and regulation of these isoforms, we first determined their expression patterns in developing mouse eyes and analyzed the role of some of them in genetic models. We found that two isoforms, A- and J-Mitf, are present throughout development in both retina and pigment epithelium, whereas H-Mitf is detected preferentially and D-Mitf exclusively in the pigment epithelium. We further found that a genomic deletion encompassing the promoter/exon regions of H-, D- and B-Mitf leads to novel mRNA isoforms and proteins translated from internal start sites. These novel proteins lack the normal, isoform-specific N-terminal sequences and are unable to support the development of the pigment epithelium, but are capable of inducing pigmentation in the ciliary margin and the iris. Moreover, in mutants of the retinal Mitf regulator Chx10 (Vsx2), reduced cell proliferation and abnormal pigmentation of the retina are associated with a preferential upregulation of H- and D-Mitf. This retinal phenotype is corrected when H- and D-Mitf are missing in double Mitf/Chx10 mutants. The results suggest that Mitf regulation in the developing eye is isoform-selective, both temporally and spatially, and that some isoforms, including H- and D-Mitf, are more crucial than others in effecting normal retina and pigment epithelium development.
Bharti
Kapil
K
Mammalian Development Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
Liu
Wenfang
W
Csermely
Tamas
T
Bertuzzi
Stefano
S
Arnheiter
Heinz
H
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D005091:Exons; D005123:Eye / Q000196:embryology* / Q000378:metabolism*; D005124:Eye Abnormalities / Q000196:embryology / Q000235:genetics / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D051739:Microphthalmia-Associated Transcription Factor / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010641:Phenotype; D010857:Pigment Epithelium of Eye / Q000196:embryology / Q000378:metabolism; D011247:Pregnancy; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
D018398:Homeodomain Proteins; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D020033:Protein Isoforms; D012333:RNA, Messenger; D014157:Transcription Factors; C088975:Vsx2 protein, mouse