Pax-6 is first expressed in a region of ectoderm anterior to the early neural plate: implications for stepwise determination of the lens.
The Pax-6 gene encodes a DNA-binding transcription factor essential to normal development of the mammalian eye. We have found that in the chick embryo, the Pax-6 gene is first expressed in a crescent-shaped region of future head ectoderm that adjoins the anterior margin of the early neural plate. As development proceeds, this region of Pax-6-positive ectoderm becomes divided into two bilateral domains. Upon contact with the optic vesicles, portions of these domains give rise to the invaginating lens placodes, which contain high levels of Pax-6 mRNA. As with mouse, rat, and zebrafish, chick Pax-6 is also expressed in the neural epithelium of the forebrain and optic vesicles. However, our results indicate that the onset of expression in the prospective head ectoderm occurs at a substantially earlier stage. Experiments involving unilateral ablation of the anterior neural plate indicate that contact with an optic vesicle is not required to maintain expression of Pax-6 in the ectoderm. Experiments in which optic vesicles have been displaced from their normal location further suggest that positioning of Pax-6 domains in the head ectoderm is independent of neighboring optic vesicles. Homozygous defects in the mouse and rat Pax-6 gene are known to cause complete failure of lens formation at the optic vesicle stage and block subsequent development of the optic cup. Our results raise the possibility that Pax-6 may be involved in the early establishment of lens-competent regions within the head ectoderm.
Li
H S
HS
Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-9289.
Yang
J M
JM
Jacobson
R D
RD
Pasko
D
D
Sundin
O
O
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002642:Chick Embryo; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D004475:Ectoderm / Q000378:metabolism; D005136:Eye Proteins; D018398:Homeodomain Proteins; D006801:Humans; D017403:In Situ Hybridization; D007908:Lens, Crystalline / Q000196:embryology* / Q000378:metabolism; D008969:Molecular Sequence Data; D009420:Nervous System / Q000196:embryology* / Q000378:metabolism; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012333:RNA, Messenger / Q000378:metabolism; D012097:Repressor Proteins
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; C000605730:PAX6 protein, human; D051761:Paired Box Transcription Factors; C000605732:Pax6 protein, mouse; C000605733:Pax6 protein, rat; D012333:RNA, Messenger; D012097:Repressor Proteins