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Eye Development and Gene Expression
Shiva Swamynathan
[email protected]
Why study eye development & gene expression?
Opaque Cornea
Iridocorneal Fusion
Keratolenticular Fusion
Peters Anomaly
FOXC1, PAX6, PITX2, or CYP1B1
Anophthalmia SOX2
Microphthalmia
PAX6, OTX2, CHX10 & RAX
Aniridia PAX6
Anophthalmia RAX
Axenfeld-Rieger
Syndrome PITX2
Cell lineage during
vertebrate eye
development
Drosophila eye transcriptome
transcription factor genes are highly expressed
Structural and pigment biosynthesis genes
genes involved in intracellular signaling,
neurotransmission, and the visual process
Transcription factor network that establishes the eye field
Whitney Heavner and Larysa Pevny. 2012.
Cold Spring Harb Perspect Biol 2012;4:a008391
Gene expression in the developing optic vesicle
Transcription factors regulating corneal development
Swamynathan, S.K. 2013. J. Ophthalmol. 103947. PMID: 23533700
Mature cornea is formed by 8-10 weeks after birth
E12.5
E17.5
E14.5
E18.5
E16.5
Adult
Number of differentially regulated genes in the
cornea between different time points
Stephens et al 2013. J. Bio. Chem. 288:34304-24
Cornea derives cells from the surface ectoderm
and neural crest mesenchyme
Swamynathan, S.K. 2013. J. Ophthalmol. 103947. PMID: 23533700
Transcription Factors in the Mouse Cornea
Highly expressed
in the cornea
KLF4
IRF1
ELF3
Ets homologous factor
HEB
KLF5
JunB
Rev-erbA-a
IRF6
Oxysterols receptor LXR-b
Pax6
Norman et al. 2004. IOVS. 45: 429-40 PMID: 14744882
Functions of Klf4 and Klf5 in the ocular surface
Wild Type
Klf4CN
Wild Type
Klf5CN
Swamynathan et al., 2007. Mol. Cell. Biol. 27:182-194
Kenchegowda et al 2011. Dev. Biol. 356:5-18
Gene, transcript and protein structure of Pax6
Pax6 regulatory networks during early eye development
Neuroectoderm lineage
Surface ectoderm lineage
Pax6 is essential for normal corneal development
Ramaesh et al., 2005. Exp.Eye Res. 81: 224-35
Corneal functions of Pax6 are dosage-dependent
Mort et al. 2011. PMID: 22220198
Role of Pitx2 in corneal development
Paired-like homeodomain transcription factor PITX2 in
E14.5
P42
PITX2 Mutants
Overabundance of mesenchyme
Malformed stroma and endothelium
Absence of anterior chamber
Corneo-lenticular fusion
Gage et al. 2014. Dev Dyn. PMID: 25044936
Pitx2 helps establish corneal avascularity
Gage et al. 2014. Dev Dyn. PMID: 25044936
Corneal epithelium and the lens are both derived
from the head surface ectoderm
Surface Ectoderm forms the
Lens & the Corneal Epithelium
Lens and Cornea Share Transcriptional Networks
Genetic pathways inducing lens differentiation
Pax6 and Sox2 cooperatively regulate
chicken δ1-crystallin gene expression
Kamachi et al 2001. Genes Dev. 15: 1272-86
Sox2 regulates cell-specific target genes
through distinct partner factors
Kamachi et al 2001. Genes Dev. 15: 1272-86
Organization of retinal circuits
Transcription factors regulating temporal
progression of mouse retinogenesis
Whitney Heavner and Larysa Pevny. 2012.
Cold Spring Harb Perspect Biol 2012;4:a008391
Stages of photoreceptor development
OTX2 plays an essential role in vertebrate retinogenesis
Otx2 expression in
developing retina
Otx2-/-
WT
Otx2-/-
WT
E12.5
E17.5
PN6
PN 0
Otx2-/-
WT
PN 9
Temporal functions of Otx2 in the mouse retina
OTX2 mutations are associated with blinding
ocular defects and brain abnormalities
OTX2 gene network in the developing retina
Xenopus
Mouse
Xenopus
Xenopus
Rx expression, phenotypes and regulation
Xenopus
Human
overexpression
Essential roles of LHX2 in eye development
• Lhx2 is a LIM domain (a double-zinc finger motif found in a variety of proteins)containing homeobox gene expressed in B-cells, forebrain and neural retina
• LHX2 coregulates the expression of Pax6, Six3 and Rax in the optic vesicle
• LHX2 is essential for eye development
Human NRL gene and protein
Nrl is required for rod photoreceptor development
Optic vesicle and RPE specification
MITF: A big gene associated with small eyes
Summary
• Large-scale expression studies suggest that about a thousand genes are
expressed in a preferential manner in the eye, compared with the rest of the body
• A series of homeobox transcription factors including Otx2, Sox2, Lhx2, Rax and
Pax6 play a major role in different stages of eye development
• Eyefield is specified in early embryos by overlapping expression of Otx2 and Sox2
in the neural ectoderm, which in turn activate expression of Lhx2, Rax and Pax6,
resulting in the formation of the optic vesicle
• Inductive interaction between neural ectoderm and surface ectoderm results in
formation of the lens placode, defined by the expression of Pax6 and Sox2
• Lens and cornea share many transcriptional networks, consistent with their origin
from the surface ectoderm
• Pitx2 and Foxc1 play major roles in anterior segment formation
• Sox2 regulates cell-specific target genes by cooperating with distinct factors such
as Pax6, Oct3/4 and Brn2
• Pax6 plays a major role in early retinogenesis, and formation of lens and cornea.
• Cone cells are the default photoreceptor cell type. NRL expression is essential for
rod cell formation
• Mitf plays a critical role in RPE formation
Expression of homeobox genes in the mature
vertebrate retina