Bharesh Chauhan, PhDResearch Assistant Professor

Dept. of Ophthalmology, UPSOM

Embryogenesis of thehuman eye 8-wk

Examples of inborn errors in human eye development

(Dr. K. Ramaesh, FRCS FRCOphthUniversity of Edinburgh)

(Dr. W.C. Caccamise, Sr, MDPittsford, NY)

(Dr. B.P. Brooks, MD PhDNEI, MD)

AniridiaAniridia AnophthalmiaAnophthalmia ColobomaColoboma

Stages in animal development

Gametogenesis

Fertilization

Cleavage

Gastrulation

Organogenesis

Growth

sperm (spermatogenesis) and ovum (oogenesis) form.

fusion of a sperm and ovum to generate a zygote.

to form morula (solid ball of blastomeres) and thenblastula (ball of cells surrounding blastocoele).

reorganization of blastocyst into a gastrula, consisting of endoderm, mesoderm and ectoderm.

organ formation from the trilaminar gastrula through the processes of patterning, differentiation, morphogenesis and growth.

correct size and shape of organs are determined by growth increating the fetus.

Organogenesis – the process

Regional specificationRegional specification

cell differentiation cell differentiation

morphogenesis morphogenesis

growth growth

Mammalian eye development

Photoreceptor neurons

Optic stalk

Developingbrain

The genetic and molecular basis of congenital eye defects.Graw J.Nat Rev Genet. 2003 Nov;4(11):876-88.

Kismet/CHD7 regulates axon morphology, memory and locomotion in a Drosophila model of CHARGE syndrome.Melicharek DJ, Ramirez LC, Singh S, Thompson R, Marenda DR.Hum Mol Genet. 2010 Nov 1;19(21):4253-64.

Origin of ocular tissuesSurface ectoderm Lacrimal gland

LensConjunctivaEyelid

Neuroectoderm NeuroretinaRPECiliary and iris epitheliumIris muscleOptic nerveVitreous

Mesoderm Extraocular musclesVascular endotheliumSchlemm's canalBloodTemporal sclera

Neural crest Corneal stromaCorneal endotheliumTrabecular meshworkCiliary body and iris stromaChoroidal stromaSclera

Surface ectoderm Lacrimal glandLensConjunctivaEyelid

Neuroectoderm NeuroretinaRPECiliary and iris epitheliumIris muscleOptic nerveVitreous

Mesoderm Extraocular musclesVascular endotheliumSchlemm's canalBloodTemporal sclera

Neural crest Corneal stromaCorneal endotheliumTrabecular meshworkCiliary body and iris stromaChoroidal stromaSclera

Neural plate patterning: upstream and downstream of the isthmic organizer.Wurst W, Bally-Cuif L.Nat Rev Neurosci. 2001 Feb;2(2):99-108.

• Prior to retinal development, the following occurs during the first 3 weeks of embryogenesis:

- neural induction of the competent ectoderm

- anterior-posterior subdivision of the resulting neural plate.

Neurulation and head patterning

Neural crest specification: migrating into genomics.Gammill LS, Bronner-Fraser M.Nat Rev Neurosci. 2003 Oct;4(10):795-805.

Stages in optic cup development

• Specification of the eye field in the diencephalon occurs at this stage by signaling between the closely-apposed:

- epithelia of the surface ectoderm

- the lateral diverticuli of the budding diencephalon.

Placode stage

• The first morphological sign of eye development in vertebrates is the bilateral evagination of the diencephalon to form the optic vesicles.

• Continued evagination leads to the formation of the optic pits with elongation of the optic stalk driving the back of the eye further.

• Mesenchyme between the optic vesicle and the surface ectoderm is displaced as the two tissues come into close physical contact.

Lens pit stage

• The continued evagination of the optic vesicle leads to the formation of the optic cup, which is bilayered.

• The upper layers differentiate to form the neural retinas and the lower layers differentiate to form the retinal pigment epithelium (RPE).

Optic cup stage

Differentiation of RPCs into retinal cell types

Intrinsically different retinal progenitor cells produce specific types of progeny.Cepko C.Nat Rev Neurosci. 2014 Sep;15(9):615-27.

• human neural retina of the optic cup inner layer differentiates within first month

• ganglion cells start first (7-8 wks) and centrally, while bipolar and horizontal cells start peripherally and migrate centrally,

• primitive fovea is formed from the thinning of the GCL and INL at 24-26 wks .

Optic stalk (OS) – choroidal fissure closure

• occurs at 6 weeks,

• molecular mechanism has been partially deciphered (eg., FGF, RA).

Optic nerve development Four phases of development

2.

• optic stalk extension

• choroidal fissure closure (coloboma),

• migration of the RGC axons into the optic stalk towards the LGN,

• reduction of axons by apoptosis (megalopapilla)

• Myelination of the axons occurs later in gestation, 32 wks in humans

3.1.

Hyaloid vasculature development

Three stage process

• deposition of hyaloid cells around lens area and generation of a loop,

• branched networks form,

• vessel refinement occurs.

In vivo analysis of hyaloid vasculature morphogenesis in zebrafish: A role for the lens in maturation and maintenance of the hyaloid.Hartsock A, Lee C, Arnold V, Gross JM.Dev Biol. 2014 Aug 13. pii: S0012-1606(14)00376-5.

placode vesicle fiberpit

a critical phase for co-ordinated morphogenesis between two epithelia, the optic vesicle and presumptive lens

Four stages of morphogenesis in lens development

RhoA

Rac1

• RhoA promotes apical constriction

• Rac1 promotes cell lengthening

Mechanism of invagination

Balanced Rac1 and RhoA activities regulate cell shape and drive invagination morphogenesis in epithelia.Chauhan BK, Lou M, Zheng Y, Lang RA.Proc Natl Acad Sci U S A. 2011 Nov 8;108(45):18289-94.

Inter-epithelial processes during lens placode invagination

Mann I. (1950) The Development of the Human Eye. 2nd Ed. Grune & Stratton, Inc. New York.

Lens pit filopodia contain active myosin II

Cdc42- and IRSp53-dependent contractile filopodia tether presumptive lens and retina to coordinate epithelial invagination.Chauhan BK, Disanza A, Choi SY, Faber SC, Lou M, Beggs HE, Scita G, Zheng Y, Lang RA.Development. 2009 Nov;136(21):3657-67.

Does the developing lens shape the optic cup?

Self-organizing optic-cup morphogenesis in three-dimensional culture.Eiraku M, Takata N, Ishibashi H, Kawada M, Sakakura E, Okuda S, Sekiguchi K, Adachi T, Sasai Y.Nature. 2011 Apr 7;472(7341):51-6.

• Shape of the cultured optic cup is different from the naturally developing optic cup next to the lens.

• Uncoupled developing lens and optic cups do not conform to canonical shape forms.

1)

Cdc42- and IRSp53-dependent contractile filopodia tether presumptive lens and retina to coordinate epithelial invagination.Chauhan BK, Disanza A, Choi SY, Faber SC, Lou M, Beggs HE, Scita G, Zheng Y, Lang RA.Development. 2009 Nov;136(21):3657-67.

2)

Maturation of the lens and sutures

https://mutagenetix.utsouthwestern.edu/phenotypic/phenotypic_rec.cfm?pk=309

Understanding the role of growth factors in embryonic development: insights from the lens.Lovicu FJ, McAvoy JW, de Iongh RU. Philos Trans R Soc Lond B Biol Sci. 2011 Apr 27;366(1568):1204-18. doi: 10.1098/rstb.2010.0339. Review.

Three-dimensional organization of primary lens fiber cells. Shestopalov VI, Bassnett S. Invest Ophthalmol Vis Sci. 2000 Mar;41(3):859-63.

• Fiber cell differentiation begins during early vesicle stage to form primary fibers in the posterior lens,

• lens continues enlarging by proliferation and elongation of the lens equator epithelial cells to form secondary fibers,

• The fibers adopt a hexagonal shape, a ball-socket mid-arrangement and are bound to the lens capsule by a foot processes

Corneal development

Neuroblastoma book edited by Hiroyuki Shimada, ISBN 978-953-51-1128-3, Published: May 29, 2013 Chapter 4 Neurotrophin and Neurotrophin Receptor Involvement in Human NeuroblastomaPierdomenico Ruggeri, Antonietta R. Farina, Lucia Cappabianca, Natalia Di Ianni, Marzia Ragone, Stefania Merolle, Alberto Gulino and Andrew R. Mackay

Angle development

The next step: detailed assessment of an adult glaucoma patient.Philippin H, Shah P, Burton M.Community Eye Health. 2012;25(79-80):50-3.

Origin of ocular tissuesSurface ectoderm Lacrimal gland

LensConjunctivaEyelid

Neuroectoderm NeuroretinaRPECiliary and iris epitheliumIris muscleOptic nerveVitreous

Mesoderm Extraocular musclesVascular endotheliumSchlemm's canalBloodTemporal sclera

Neural crest Corneal stromaCorneal endotheliumTrabecular meshworkCiliary body and iris stromaChoroidal stromaSclera

Surface ectoderm Lacrimal glandLensConjunctivaEyelid

Neuroectoderm NeuroretinaRPECiliary and iris epitheliumIris muscleOptic nerveVitreous

Mesoderm Extraocular musclesVascular endotheliumSchlemm's canalBloodTemporal sclera

Neural crest Corneal stromaCorneal endotheliumTrabecular meshworkCiliary body and iris stromaChoroidal stromaSclera