Build me up optic cup: Intrinsic and extrinsic mechanisms of vertebrate eye morphogenesis

The transformation of the oval optic vesicle to a hemispheric bi-layered optic cup involves major morphological changes during early vertebrate eye development. According to the classical view, the lens-averted epithelium differentiates into the retinal pigmented epithelium (RPE), while the lens-facing epithelium forms the neuroretina. We find a 4.7 fold increase of the entire basal surface of the optic cup. Although the area an individual RPC demands at its basal surface declines during optic cup formation, we find a 4.7 fold increase of the entire basal surface of the optic cup. We demonstrate that the lens-averted epithelium functions as reservoir and contributes to the growing neuroretina by epithelial flow around the distal rims of the optic cup. This flow is negatively modulated by BMP, which arrests epithelial flow. This inhibition results in persisting neuroretina in the RPE domain and ultimately in coloboma.

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Developmental delay during eye morphogenesis underlies optic cup and neurogenesis defects in mab21l2u517 zebrafish mutants

The International Journal of Developmental Biology ◽

10.1387/ijdb.200173lv ◽

2020 ◽

Vol 52 ◽

Cited By ~ 1

Author(s):

Rebecca Wycliffe ◽

Julie Plaisancie ◽

Sydney Leaman ◽

Octavia Santis ◽

Lisa Tucker ◽

...

Keyword(s):

Developmental Delay ◽

Marginal Zone ◽

Tissue Cell ◽

Asynchronous Development ◽

Optic Cup ◽

Organ Specific ◽

Optic Vesicles ◽

Vertebrate Eye ◽

Ciliary Marginal Zone ◽

Eye Morphogenesis

Background: Shaping the vertebrate eye requires evagination of the optic vesicles. These vesicles subsequently fold into optic cups prior to undergoing neurogenesis and allocating a population of late progenitors at the margin of the eye. mab21l2 encodes a protein of unknown biological function expressed in the developing optic vesicles, and loss of mab21l2 function results in malformed eyes. The bases of these defects are, however, poorly understood. Methods: To further study mab21l2 we used CRISPR/Cas9 to generate a new zebrafish mutant allele (mab21l2u517). We characterized eye morphogenesis and neurogenesis upon loss of mab21l2 function using tissue/cell-type-specific transgenes and immunostaining, in situ hybridization and bromodeoxyuridine incorporation. Results: mab21l2u517 eyes fail to grow properly and display an excess of progenitors in the ciliary marginal zone. The expression of a transgene reporter for the vsx2 gene –a conserved marker for retinal progenitors– was delayed in mutant eyes and accompanied by disruptions in the epithelial folding that fuels optic cup morphogenesis. Mutants also displayed nasal-temporal malformations suggesting asynchronous development along that axis. Consistently, nasal retinal neurogenesis initiated but did not propagate in a timely fashion to the temporal retina. Later in development, mutant retinas did laminate and differentiate. Thus, mab21l2u517 mutants present a complex eye morphogenesis phenotype characterized by an organ-specific developmental delay. Conclusions: We propose that mab21l2 facilitates optic cup development with consequences both for timely neurogenesis and allocation of progenitors to the zebrafish ciliary marginal zone. These results confirm and extend previous analyses supporting the role of mab21l2 in coordinating morphogenesis and differentiation in developing eyes.

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The Xenopus homologue of the Drosophila gene tailless has a function in early eye development

Development ◽

10.1242/dev.125.13.2425 ◽

1998 ◽

Vol 125 (13) ◽

pp. 2425-2432 ◽

Cited By ~ 4

Author(s):

T. Hollemann ◽

E. Bellefroid ◽

T. Pieler

Keyword(s):

Eye Development ◽

Neural Plate ◽

Regulatory Function ◽

Genetic Circuits ◽

Optic Stalk ◽

Drosophila Gene ◽

Ciliary Margin ◽

Evolutionarily Conserved ◽

Optic Cup ◽

Vertebrate Eye

Genetic circuits responsible for the development of photoreceptive organs appear to be evolutionarily conserved. Here, the Xenopus homologue Xtll of the Drosophila gene tailless (tll), which we find to be expressed during early eye development, is characterized with respect to its relationship to vertebrate regulators of eye morphogenesis, such as Pax6 and Rx. Expression of all three genes is first detected in the area corresponding to the eye anlagen within the open neural plate in partially overlapping, but not identical, patterns. During the evagination of the optic vesicle, Xtll expression is most prominent in the optic stalk, as well as in the distal tip of the forming vesicle. In tadpole-stage embryos, Xtll gene transcription is most prominent in the ciliary margin of the optic cup. Inhibition of Xtll function in Xenopus embryos interferes specifically with the evagination of the eye vesicle and, in consequence, Xpax6 gene expression is severely reduced in such manipulated embryos. These findings suggest that Xtll serves an important regulatory function in the earliest phases of vertebrate eye development.

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The Msh-like homeobox genes define domains in the developing vertebrate eye

Development ◽

10.1242/dev.112.4.1053 ◽

1991 ◽

Vol 112 (4) ◽

pp. 1053-1061 ◽

Cited By ~ 8

Author(s):

A.P. Monaghan ◽

D.R. Davidson ◽

C. Sime ◽

E. Graham ◽

R. Baldock ◽

...

Keyword(s):

Mouse Embryo ◽

Ciliary Body ◽

Cellular Differentiation ◽

Temporal Relationship ◽

Chromosomal Location ◽

Neural Retina ◽

Optic Vesicle ◽

Surface Ectoderm ◽

Optic Cup ◽

Vertebrate Eye

The mouse Hox-7.1 gene has previously been shown to be related to the Drosophila Msh homeobox-containing gene. Here we report the isolation of a new member of this family which resides at an unlinked chromosomal location and has been designated Hox-8.1. Both Hox-7.1 and Hox-8.1 are expressed in the mouse embryo during the early stages of eye development in a distinct spatial and temporal relationship. Hox-8.1 is expressed in the surface ectoderm and in the optic vesicle before invagination occurs in regions corresponding to the prospective corneal epithelium and neural retina, respectively. Hox-7.1 is expressed after formation of the optic cup, marking the domain that will give rise to the ciliary body. The activity of these genes indicates that the inner layer of the optic cup is differentiated into three distinct compartments before overt cellular differentiation occurs. Our results suggest that these genes are involved in defining the region that gives rise to the inner layer of the optic cup and in patterning this tissue to define the iris, ciliary body and retina.

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Patterning the Vertebrate Retina with Morphogenetic Signaling Pathways

The Neuroscientist ◽

10.1177/1073858419874016 ◽

2019 ◽

Vol 26 (2) ◽

pp. 185-196 ◽

Cited By ~ 7

Author(s):

Marcos J. Cardozo ◽

María Almuedo-Castillo ◽

Paola Bovolenta

Keyword(s):

Signaling Pathways ◽

Pigment Epithelium ◽

Retinal Pigment ◽

Subsequent Development ◽

Neural Retina ◽

Bmp Signaling ◽

Vertebrate Species ◽

Optic Stalk ◽

Optic Cup ◽

Vertebrate Eye

The primordium of the vertebrate eye is composed of a pseudostratified and apparently homogeneous neuroepithelium, which folds inward to generate a bilayered optic cup. During these early morphogenetic events, the optic vesicle is patterned along three different axes—proximo-distal, dorso-ventral, and naso-temporal—and three major domains: the neural retina, the retinal pigment epithelium (RPE), and the optic stalk. These fundamental steps that enable the subsequent development of a functional eye, entail the precise coordination among genetic programs. These programs are driven by the interplay of signaling pathways and transcription factors, which progressively dictate how each tissue should evolve. Here, we discuss the contribution of the Hh, Wnt, FGF, and BMP signaling pathways to the early patterning of the retina. Comparative studies in different vertebrate species have shown that their morphogenetic activity is repetitively used to orchestrate the progressive specification of the eye with evolutionary conserved mechanisms that have been adapted to match the specific need of a given species.

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Eye morphogenesis driven by epithelial flow into the optic cup facilitated by modulation of bone morphogenetic protein

eLife ◽

10.7554/elife.05216 ◽

2015 ◽

Vol 4 ◽

Cited By ~ 45

Author(s):

Stephan Heermann ◽

Lucas Schütz ◽

Steffen Lemke ◽

Kerstin Krieglstein ◽

Joachim Wittbrodt

Keyword(s):

Marginal Zone ◽

Eye Development ◽

Optic Vesicle ◽

Basal Surface ◽

Morphogenetic Protein ◽

Retinal Determination ◽

Optic Cup ◽

Morphological Transformations ◽

Vertebrate Eye ◽

Ciliary Marginal Zone

The hemispheric, bi-layered optic cup forms from an oval optic vesicle during early vertebrate eye development through major morphological transformations. The overall basal surface, facing the developing lens, is increasing, while, at the same time, the space basally occupied by individual cells is decreasing. This cannot be explained by the classical view of eye development. Using zebrafish (Danio rerio) as a model, we show that the lens-averted epithelium functions as a reservoir that contributes to the growing neuroretina through epithelial flow around the distal rims of the optic cup. We propose that this flow couples morphogenesis and retinal determination. Our 4D data indicate that future stem cells flow from their origin in the lens-averted domain of the optic vesicle to their destination in the ciliary marginal zone. BMP-mediated inhibition of the flow results in ectopic neuroretina in the RPE domain. Ultimately the ventral fissure fails to close resulting in coloboma.

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Cell motility and polarity during vertebrate eye morphogenesis

Developmental Biology ◽

10.1016/j.ydbio.2009.05.223 ◽

2009 ◽

Vol 331 (2) ◽

pp. 446

Author(s):

Kristen M. Kwan ◽

Chi-Bin Chien

Keyword(s):

Cell Motility ◽

Vertebrate Eye ◽

Eye Morphogenesis

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Analysis of cellular behavior and cytoskeletal dynamics reveal a constriction mechanism driving optic cup morphogenesis

eLife ◽

10.7554/elife.15797 ◽

2016 ◽

Vol 5 ◽

Cited By ~ 33

Author(s):

María Nicolás-Pérez ◽

Franz Kuchling ◽

Joaquín Letelier ◽

Rocío Polvillo ◽

Jochen Wittbrodt ◽

...

Keyword(s):

Laser Cutting ◽

Mechanical Tension ◽

Cellular Behavior ◽

Optic Cup ◽

Tensile Forces ◽

Cytoskeletal Dynamics ◽

Cellular Machinery ◽

Vertebrate Eye ◽

Fast Oscillations ◽

Developmental Window

Contractile actomyosin networks have been shown to power tissue morphogenesis. Although the basic cellular machinery generating mechanical tension appears largely conserved, tensions propagate in unique ways within each tissue. Here we use the vertebrate eye as a paradigm to investigate how tensions are generated and transmitted during the folding of a neuroepithelial layer. We record membrane pulsatile behavior and actomyosin dynamics during zebrafish optic cup morphogenesis by live imaging. We show that retinal neuroblasts undergo fast oscillations and that myosin condensation correlates with episodic contractions that progressively reduce basal feet area. Interference with lamc1 function impairs basal contractility and optic cup folding. Mapping of tensile forces by laser cutting uncover a developmental window in which local ablations trigger the displacement of the entire tissue. Our work shows that optic cup morphogenesis is driven by a constriction mechanism and indicates that supra-cellular transmission of mechanical tension depends on ECM attachment.

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Nf2 fine-tunes proliferation and tissue alignment during closure of the optic fissure in the embryonic mouse eye

10.1101/2020.06.28.176065 ◽

2020 ◽

Author(s):

Wesley R. Sun ◽

Sara Ramirez ◽

Kelly E. Spiller ◽

Yan Zhao ◽

Sabine Fuhrmann

Keyword(s):

Cell Fate ◽

Hippo Pathway ◽

Cell Number ◽

Cancer Development ◽

Developmentally Regulated ◽

Ferm Domain ◽

Embryonic Mouse ◽

Ocular Abnormalities ◽

Optic Cup ◽

Eye Morphogenesis

AbstractUveal coloboma represents one of the most common congenital ocular malformations accounting for up to 10% of childhood blindness (1~ in 5,000 live birth). Coloboma originates from defective fusion of the optic fissure (OF), a transient gap that forms during eye morphogenesis by asymmetric, ventral invagination. Genetic heterogeneity combined with the activity of developmentally regulated genes suggest multiple mechanisms regulating OF closure. The tumor suppressor and FERM domain protein neurofibromin 2 (NF2) controls diverse processes in cancer, development and regeneration, via Hippo pathway and cytoskeleton regulation. In humans, NF2 mutations can cause ocular abnormalities, including coloboma, however, its actual role in OF closure is unknown. Using conditional inactivation in the embryonic mouse eye, our data indicates that loss of Nf2 function results in a novel underlying cause for coloboma. In particular, mutant eyes show substantially increased RPE proliferation in the fissure region with concomitant acquisition of RPE cell fate. Cells lining the OF margin can maintain RPE fate ectopically and fail to transition from neuroepithelial to cuboidal shape. In the dorsal RPE of the optic cup, Nf2 inactivation leads to a robust increase in cell number, with local disorganization of the cytoskeleton components F-actin and pMLC2. We propose that RPE hyperproliferation is the primary cause for the observed defects causing insufficient alignment of the OF margins in Nf2 mutants and failure to fuse properly, resulting in persistent coloboma. Our findings indicate that limiting proliferation particularly in the RPE layer is a critical mechanism during optic fissure closure.

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Localization of Tfap2β, Casq2, Penk, Zic1, and Zic3 Expression in the Developing Retina, Muscle, and Sclera of the Embryonic Mouse Eye

Journal of Histochemistry & Cytochemistry ◽

10.1369/0022155419885112 ◽

2019 ◽

Vol 67 (12) ◽

pp. 863-871

Author(s):

Yong Wan ◽

Casey White ◽

Nadine Robert ◽

Matthew B. Rogers ◽

Heather L. Szabo-Rogers

Keyword(s):

Calcium Binding ◽

Expression Patterns ◽

Cell Types ◽

Neural Retina ◽

Craniofacial Development ◽

Optic Disk ◽

Embryonic Mouse ◽

Optic Cup ◽

Unique Cell ◽

Eye Morphogenesis

Optic development involves sequential interactions between several different tissue types, including the overlying ectoderm, adjacent mesoderm, and neural crest mesenchyme and the neuroectoderm. In an ongoing expression screen, we identified that Tfap2β, Casq2, Penk, Zic1, and Zic3 are expressed in unique cell types in and around the developing eye. Tfap2β, Zic1, and Zic3 are transcription factors, Casq2 is a calcium binding protein and Penk is a neurotransmitter. Tfap2β, Zic1, and Zic3 have reported roles in brain and craniofacial development, while Casq2 and Penk have unknown roles. These five genes are expressed in the major tissue types in the eye, including the muscles, nerves, cornea, and sclera. Penk expression is found in the sclera and perichondrium. At E12.5 and E15.5, the extra-ocular muscles express Casq2, the entire neural retina expresses Zic1, and Zic3 is expressed in the optic disk and lip of the optic cup. The expression of Tfap2β expanded from corneal epithelium to the neural retina between E12.5 to E15.5. These genes are expressed in similar domains as Hedgehog ( Gli1, and Ptch1) and the Wnt ( Lef1) pathways. The expression patterns of these five genes warrant further study to determine their role in eye morphogenesis:

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