The homeobox gene mbx is involved in eye and tectum development.
The homeobox gene mbx is first activated at the end of gastrulation in zebrafish in the presumptive forebrain and midbrain region. During somitogenesis stages, the anterior expression of mbx, which partly overlaps the future eye field, gradually decreases, while midbrain expression intensifies and becomes restricted to the presumptive tectum. Knockdown of mbx expression by morpholino antisense oligonucleotides (mbx-MO) leads to a reduction in the size of the eyes and tectum. Expression domains of rx1 and pax6 in the eye field and of mab21l2 in the eye field and tectum anlage were reduced in size in mbx-MO-injected embryos by somitogenesis stages. Further, induction of islet1 and lim3 expression in the eye at 2 days postfertilization (dpf) was suppressed in mbx-MO-injected embryos. In mbx-MO-injected embryos at 2-5 dpf, the lamination of the eye was disorganized and the number of retinal axons was substantially reduced, but the few remaining axons navigated appropriately to the contralateral tectum. A chimeric protein composed of the Mbx DNA-binding domain and the VP16 activation domain affected eye and tectum development similarly to mbx-MO knockdown, suggesting that Mbx acts as a transcriptional repressor in the zebrafish embryo. Based on these data, we propose that the mbx homeobox gene is required for the development of the eyes and tectum.
Kawahara
Atsuo
A
Laboratory of Molecular Genetics, National Institute of Child Health and Human Development/NIH, Bethesda, MD 20892, USA. kawahara@exchange.nih.gov
Chien
Chi-Bin
CB
Dawid
Igor B
IB
D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001921:Brain / Q000196:embryology; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005123:Eye / Q000196:embryology*; D005136:Eye Proteins; D005775:Gastrula / Q000378:metabolism; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D006801:Humans; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D008856:Microscopy, Fluorescence; D008938:Mitosis; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000494:pharmacology; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D010641:Phenotype; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013477:Superior Colliculi / Q000196:embryology*; D013997:Time Factors; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
C464523:Dmbx1a protein, zebrafish; D005136:Eye Proteins; D018398:Homeodomain Proteins; D009841:Oligonucleotides; D000071841:PAX6 Transcription Factor; C000605730:PAX6 protein, human; D051761:Paired Box Transcription Factors; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029961:Zebrafish Proteins; C464524:rx1 protein, zebrafish