Role of apoptosis in eyelid development

Making the head: Caspases in life and death

The term apoptosis, as a way of programmed cell death, was coined a half century ago and since its discovery the process has been extensively investigated. The anatomy and physiology of the head are complex and thus apoptosis has mostly been followed in separate structures, tissues or cell types. This review aims to provide a comprehensive overview of recent knowledge concerning apoptosis-related molecules involved in the development of structures of head with a particular focus on caspases, cysteine proteases having a key position in apoptotic pathways. Since many classical apoptosis-related molecules, including caspases, are emerging in several non-apoptotic processes, these were also considered. The largest organ of the head region is the brain and its development has been extensively investigated, including the roles of apoptosis and related molecules. Neurogenesis research also includes sensory organs such as the eye and ear, efferent nervous system and associated muscles and glands. Caspases have been also associated with normal function of the skin and hair follicles. Regarding mineralised tissues within craniofacial morphogenesis, apoptosis in bones has been of interest along with palate fusion and tooth development. Finally, the role of apoptosis and caspases in angiogenesis, necessary for any tissue/organ development and maintenance/homeostasis, are discussed. Additionally, this review points to abnormalities of development resulting from improper expression/activation of apoptosis-related molecules.

A Systematic Approach of the Intrauterine Morphogenesis of the Human Palpebral Apparatus

The human eyelid embodies a vast diversity of functions. Acting as a protective shield for the ocular apparatus and as a light regulator in the sight process, eyelids stand a fascinating - yet omitted - role in facial aesthetics, serving as a racial trait by which humankind succeeded to manifest heterogeneity as a species. These assumptions are precisely forecasted right from in-utero life through intricate processes of growth and cell differentiation. In the Department of Anatomy of "Carol Davila" University of Medicine and Pharmacy, we performed morphological assessments on 41 embryos and fetuses with gestational ages ranging from 6 to 29 weeks. This study aims to illustrate the morphogenesis of eyelids in human embryos and fetuses and highlight macroscopic features which could potentially have significant clinical implications in ophthalmic pathology.

Embryologic and Fetal Development of the Eyelid and the Lacrimal Drainage System

The embryological and fetal morphogenesis of the eyelids and lacrimal drainage system is multifactorial and complex. This protracted process begins in the 5th week of prenatal life and involves a successive series of subtle and tightly regulated morphogenetic events. Major milestones of the embryological and fetal development of the eyelids include the beginning of eyelid formation during the 6th week, eyelid fusion by the 8th week, and the development of eyelid structures beginning in the 9th week (immediately following eyelid fusion), with progression until eyelid separation by the 24th week. After eyelid separation, the eyelids begin to assume their newly developed shape. Around the 32nd week, eyelids are almost fully developed and fully separated but still visibly closed. Key development steps of the lacrimal drainage system include formation of the lacrimal lamina (the primordium of the future lacrimal system) and the lacrimal cord (the primordium of the lacrimal canaliculi) in the 7th week, with canalization starting from the 10th week. During the 10th week, the excretory lacrimal system displays a lumen with a true lacrimal duct that can be distinguished. The epithelium of the lacrimal canaliculi is in contact with the palpebral conjunctival epithelium. The two epithelia form a continuous epithelial lamina. The caudal extreme of the lacrimal duct and the inferior meatal lamina join and the latter begins to cavitate. Understanding this multidimensional process of development in prenatal life, as well as identifying and linking signaling cascades and regulatory genes to existing diseases, may pave the way for developing minimally invasive interventions and scar reducing surgical methods, controlling the spread of malignancies, and the use of progenitor/stem cell and even regenerative therapy.

Genetic Control of MAP3K1 in Eye Development and Sex Differentiation

The MAP3K1 is responsible for transmitting signals to activate specific MAP2K-MAPK cascades. Following the initial biochemical characterization, genetic mouse models have taken center stage to elucidate how MAP3K1 regulates biological functions. To that end, mice were generated with the ablation of the entire Map3k1 gene, the kinase domain coding sequences, or ubiquitin ligase domain mutations. Analyses of the mutants identify diverse roles that MAP3K1 plays in embryonic survival, maturation of T/B cells, and development of sensory organs, including eye and ear. Specifically in eye development, Map3k1 loss-of-function was found to be autosomal recessive for congenital eye abnormalities, but became autosomal dominant in combination with Jnk and RhoA mutations. Additionally, Map3k1 mutation increased eye defects with an exposure to environmental agents such as dioxin. Data from eye developmental models reveal the nexus role of MAP3K1 in integrating genetic and environmental signals to control developmental activities. Here, we focus the discussions on recent advances in understanding the signaling mechanisms of MAP3K1 in eye development in mice and in sex differentiation from human genomics findings. The research works featured here lead to a deeper understanding of the in vivo signaling network, the mechanisms of gene-environment interactions, and the relevance of this multifaceted protein kinase in disease etiology and pathogenesis.

Role of EGF receptor signaling on morphogenesis of eyelid and meibomian glands

The epidermal growth factor receptor (EGFR) signaling has a pivotal role in the regulation of morphogenesis during development and maintenance of homeostasis in adult eyelid and its adnexa. Studies have demonstrated that during eyelid morphogenesis the EGFR signaling pathway is responsible for keratinocyte and mesenchymal cell proliferation and migration at the eyelid tip. For meibomian gland morphogenesis, EGFR signaling activation stimulates meibomian gland epithelial cell proliferation. EGFR signaling pathway functions through multiple downstream signals such as ERK, Rho/ROCK and integrin and is regulated by a variety of upstream signals including Adam17, GPR48 and FGFR signaling. Herein we review the literature that describe the role of EGFR and its related signaling pathways in eyelid and meibomian gland morphogenesis.

Pre- and Postnatal Development of the Eye: A Species Comparison

In this review paper, literature data on pre- and postnatal eye development are compared between humans and nonclinical species that are commonly used for human safety assessment, namely, mouse, rat, rabbit, dog, minipig, and nonhuman primates. Some new data on rat and minipig ocular development are also included. This compiled information can be helpful for species selection in juvenile toxicity studies or assist in the interpretation of (non)clinical data during pediatric drug development. Despite some differences in developmental windows and anatomical peculiarities, such as the lack of a fovea centralis in nonprimate species or the presence of a nictitating membrane in some nonclinical species, the functioning and development of the eye is strikingly similar between humans and other mammals. As such, all commonly used nonclinical species appear to be relatively good models for human eye development, although some practical constraints such as size may be a limiting factor. Birth Defects Research 109:1540-1567, 2017. © 2017 Wiley Periodicals, Inc.

Embryologic and Fetal Development of the Human Eyelid

Purpose:

To review the recent data about eyelid morphogenesis, and outline a timeline for eyelid development from the very early stages during embryonic life till final maturation of the eyelid late in fetal life.

Methods:

The authors extensively review major studies detailing human embryologic and fetal eyelid morphogenesis. These studies span almost a century and include some more recent cadaver studies. Numerous studies in the murine model have helped to better understand the molecular signals that govern eyelid embryogenesis. The authors summarize the current findings in molecular biology, and highlight the most significant studies in mice regarding the multiple and interacting signaling pathways involved in regulating normal eyelid morphogenesis.

Results:

Eyelid morphogenesis involves a succession of subtle yet strictly regulated morphogenetic episodes of tissue folding, proliferation, contraction, and even migration, which may occur simultaneously or in succession.

Conclusions:

Understanding the extraordinary process of building eyelid tissue in embryonic life, and deciphering its underlying signaling machinery has far reaching clinical implications beyond understanding the developmental abnormalities involving the eyelids, and may pave the way for achieving scar-reducing therapies in adult mammalian wounds, or control the spread of malignancies.

The authors describe in detail the recent advances in the knowledge of embryological and fetal development of the eyelids, and briefly outline the molecular basis of eyelid morphogenesis.

Genome-Wide Association Identifies SLC2A9 and NLN Gene Regions as Associated with Entropion in Domestic Sheep

Entropion is an inward rolling of the eyelid allowing contact between the eyelashes and cornea that may lead to blindness if not corrected. Although many mammalian species, including humans and dogs, are afflicted by congenital entropion, no specific genes or gene regions related to development of entropion have been reported in any mammalian species to date. Entropion in domestic sheep is known to have a genetic component therefore, we used domestic sheep as a model system to identify genomic regions containing genes associated with entropion. A genome-wide association was conducted with congenital entropion in 998 Columbia, Polypay, and Rambouillet sheep genotyped with 50,000 SNP markers. Prevalence of entropion was 6.01%, with all breeds represented. Logistic regression was performed in PLINK with additive allelic, recessive, dominant, and genotypic inheritance models. Two genome-wide significant (empirical P<0.05) SNP were identified, specifically markers in SLC2A9 (empirical P = 0.007; genotypic model) and near NLN (empirical P = 0.026; dominance model). Six additional genome-wide suggestive SNP (nominal P<1x10^-5) were identified including markers in or near PIK3CB (P = 2.22x10^-6; additive model), KCNB1 (P = 2.93x10^-6; dominance model), ZC3H12C (P = 3.25x10^-6; genotypic model), JPH1 (P = 4.68x20^-6; genotypic model), and MYO3B (P = 5.74x10^-6; recessive model). This is the first report of specific gene regions associated with congenital entropion in any mammalian species, to our knowledge. Further, none of these genes have previously been associated with any eyelid traits. These results represent the first genome-wide analysis of gene regions associated with entropion and provide target regions for the development of sheep genetic markers for marker-assisted selection.

Congenital upper eyelid coloboma: embryologic, nomenclatorial, nosologic, etiologic, pathogenetic, epidemiologic, clinical, and management perspectives

Purpose:

To review the recent literature and describe the authors’ experience with congenital upper eyelid coloboma.

Methods:

In this review, we will summarize the embryologic and etiopathogenetic bases of congenital upper eyelid coloboma, and study the published clinical reports. We will also attempt to briefly shed some light on the rarer syndromic curiosities associated with upper eyelid coloboma.

Results:

Congenital upper eyelid colobomas are one of the few nontraumatic oculoplastic emergencies that may occasionally present in the first few days of life with a corneal ulcer and may even present with impending perforation. They can present with or without corneopalpebral adhesions, may be isolated findings or a part of a larger spectrum of congenital anomalies as in the case of Fraser syndrome or Goldenhar syndrome, or could be associated with other rare curiosities that could challenge the clinician with a huge diagnostic dilemma.

Conclusions:

Existing literature dealing with congenital colobomas of the upper eyelid is fraught with nosologic problems, confusing etiologies, and overlapping clinical features. We attempted to clarify the salient clinical features, outline the management principles, and until a time in the not-so-distant future where advances in molecular genetic testing would help redefine the etiology and the diverse clinical spectrum of genetic diseases associated with upper eyelid colobomas, we propose a simplified classification scheme based on the relation of the coloboma to the cornea, the presence or absence of systemic features, and all the syndromic and nonsyndromic associations of congenital coloboma of the upper eyelid known today.

In this review, the authors will describe the pathogenesis of upper eyelid coloboma, suggest a new simplified classification system, describe the clinical picture in detail, clarify the various syndromic associations of upper eyelid coloboma, and lay out the basic surgical principles of management.

Epithelial sheet movement requires the cooperation of c-Jun and MAP3K1

Epithelial sheet movement is an essential morphogenetic process during mouse embryonic eyelid closure in which Mitogen-Activated Protein 3 Kinase 1 (MAP3K1) and c-Jun play a critical role. Here we show that MAP3K1 associates with the cytoskeleton, activates Jun N-terminal kinase (JNK) and actin polymerization, and promotes the eyelid inferior epithelial cell elongation and epithelium protrusion. Following epithelium protrusion, c-Jun begins to express and acts to promote ERK phosphorylation and migration of the protruding epithelial cells. Homozygous deletion of either gene causes defective eyelid closure, but non-allelic non-complementation does not occur between Map3k1 and c-Jun and the double heterozygotes have normal eyelid closure. Results from this study suggest that MAP3K1 and c-Jun signal through distinct temporal-spatial pathways and that productive epithelium movement for eyelid closure requires the consecutive action of MAP3K1-dependent cytoskeleton reorganization followed by c-Jun-mediated migration.

Expression of signaling components in embryonic eyelid epithelium

Closure of an epithelium opening is a critical morphogenetic event for development. An excellent example for this process is the transient closure of embryonic eyelid. Eyelid closure requires shape change and migration of epithelial cells at the tip of the developing eyelids, and is dictated by numerous signaling pathways. Here we evaluated gene expression in epithelial cells isolated from the tip (leading edge, LE) and inner surface epithelium (IE) of the eyelid from E15.5 mouse fetuses by laser capture microdissection (LCM). We showed that the LE and IE cells are different at E15.5, such that IE had higher expression of muscle specific genes, while LE acquired epithelium identities. Despite their distinct destinies, these cells were overall similar in expression of signaling components for the “eyelid closure pathways”. However, while the LE cells had more abundant expression of Fgfr2, Erbb2, Shh, Ptch1 and 2, Smo and Gli2, and Jag1 and Notch1, the IE cells had more abundant expression of Bmp5 and Bmpr1a. In addition, the LE cells had more abundant expression of adenomatosis polyposis coli down-regulated 1 (Apcdd1), but the IE cells had high expression of Dkk2. Our results suggest that the functionally distinct LE and IE cells have also differential expression of signaling molecules that may contribute to the cell-specific responses to morphogenetic signals. The expression pattern suggests that the EGF, Shh and NOTCH pathways are preferentially active in LE cells, the BMP pathways are effective in IE cells, and the Wnt pathway may be repressed in LE and IE cells via different mechanisms.

[Ankyloblepharon filiforme adnatum]

The ankyloblepharon filiforme adnatum is a congenital eyelid anomaly in which the development of the eyelids is completed but the eyelids are not completely separated at birth. The abnormality can occur as an isolated anomaly, together with other eye diseases or in the context of systemic syndromes. In this case report the current classification and essential diagnostics of AFA will be reviewed.

Timetable for upper eyelid development in staged human embryos and fetuses

In this study, we examined the development of the upper eyelids to provide a basic understanding of gross anatomical structures and information relative to mechanisms of congenital anomalies in the upper eyelids. We studied the upper eyelids by external and histological observation in 48 human embryos and in fetuses from 5 to 36 weeks postfertilization. The upper eyelid fold began to develop at Stage 18. Upper and lower eyelids fused from the lateral cantus at Stage 22, and fusion was complete by 9 weeks of development. Mesenchymal condensations forming the orbital part of the orbicularis oculi (OO), tarsal plate, and the eyelashes and their appendages, were first seen at Week 9. Definite muscle structures of the upper eyelid, such as the orbital part of the OO and the levator palpebrae superioris and its aponeurosis, and the Müller's muscle were observed at 12 and 14 weeks, respectively. In addition, orbital septum, arterial arcade and orbital fat pad, and tarsal gland (TG) were apparent at 12, 14, and 18 weeks, respectively. Opening of the palpebral fissure was observed at Week 20. In addition, we defined the directional orientation between the levator aponeurosis and orbital septum and the growth pattern of the TG. Our results will be helpful in understanding the normal development of the upper eyelid and the origins of upper eyelid birth defects.

Hay-Wells syndrome: a case report

Hay-Wells syndrome is a rare form of ectodermal dysplasia initially described by Hay and Wells in 1976. It is an autosomal dominant disorder with varying forms of expression featuring congenital abnormalities of the skin, hair, teeth, nails and sweat glands. The present report describes the case of a 17-year old white boy, the son of nonconsanguineous parents, who presented ankyloblepharon filiforme adnatum, ectodermal dysplasia and a cleft palate at birth, which are considered cardinal signs of this syndrome by most authors. We also highlight the importance of implementing multidisciplinary follow-up of these patients.

A newborn with ankyloblepharon filiforme adnatum: a case report

Ankyloblepharon filiforme adnatum is a rare congenital anomaly. We report a case of ankyloblepharon filiforme adnatum in a newborn Caucasian male whose paediatric examination was otherwise unremarkable. Ankyloblepharon filiforme adnatum can present as an isolated finding, in association with other anomalies, or as part of a well-defined syndrome.

Bilateral Complete Isolated Cryptophthalmos: A Case Report

Cryptophthalmos is a condition of congenital eyelid malformation most commonly accompanied by syndactyly, urogenital anomalies, and cognitive impairments as in Fraser syndrome. We report on a patient with characteristic features consistent with autosomal dominant bilateral complete isolated cryptophthalmos. This patient represents only the sixth documented case of bilateral complete isolated cryptophthalmos. Defining characteristics of this variety are discussed, including bilateral central dimpling over the globes, normal eyebrow growth, and the absence of cognitive impairment. We introduce phenotypic features that distinguish bilateral isolated cryptophthalmos from other forms and discuss its relatively favorable prognosis.