Morphogenesis of the human lacrimal gland

Advances in lacrimal gland organoid development: Techniques and therapeutic applications

The human lacrimal gland (LG), located above the outer orbital region within the frontal bone socket, is essential in maintaining eye surface health and lubrication. It is firmly anchored to the orbital periosteum by the connective tissue, and it is vital for protecting and lubricating the eye by secreting lacrimal fluid. Disruption in the production, composition, or secretion of lacrimal fluid can lead to dry eye syndrome, a condition characterized by ocular discomfort and potential eye surface damage. This review explores the recent advancements in LG organoid generation using tissues and stem cells, highlighting cutting-edge techniques in biomaterial-based and scaffold-free technologies. Additionally, we shed light on the complex pathophysiology of LG dysfunction, providing insights into the LG physiological roles while identifying strategies for generating LG organoids and exploring their potential clinical applications. Alterations in LG morphology or secretory function can affect the tear film stability and quality, leading to various ocular pathological conditions. This comprehensive review underlines the critical crosslink of LG organoid development with disease modeling and drug screening, underscoring their potential for advancing therapeutic applications.

Aesthetic and Functional Outcomes of Upper Blepharoplasty Combined with Dacryoadenopexy in Lacrimal Gland Prolapse

INTRODUCTION

Lacrimal gland prolapse (LGP) is a term used to describe a benign, anterior displacement of the lacrimal gland. If this condition is not properly addressed during upper blepharoplasty, the aesthetic and functional results are less than optimal. This study aimed to report the surgical outcomes of upper blepharoplasty combined with dacryoadenopexy in patients with LGP.

METHODS

We reported an unusual case of severe LGP in a young patient. In addition, we performed a systematic review of the English literature on surgical cases of LGP published between 1973 and 2023. Eligible articles were analyzed for individual patient data (IPD) and aggregate patient data (APD). The primary predictor variable was the surgical technique used for lacrimal gland repositioning/suspension. The primary outcome variable was relapse rate.

RESULTS

The bibliographic search retrieved 488 surgical cases of LGP: 12 in IPD, and 476 in APD datasets. The relapse rates in the IPD and APD cohorts were 8.3% (1/12) and 1.2% (6/476), respectively. Within the APD dataset, no significant difference in the relapse rates between dacryoadenopexy via suture suspension and Whitnall's ligament suspension (5/409 and 1/20, respectively; P > 0.05) was observed. Light cauterization of the lacrimal gland capsule and surrounding soft tissues was performed in mild LGP cases (< 4 mm prolapse), with a relapse rate of 0% (0/47).

CONCLUSION

Upper blepharoplasty combined with dacryoadenopexy proved to be a safe surgical procedure with very satisfactory aesthetic outcome and minimal relapse rate.

LEVEL OF EVIDENCE III

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Isolated Congenital Lacrimal Gland Agenesis

Congenital alacrima is an uncommon condition marked by a lack of tear production that is present from birth. This condition often occurs in conjunction with various syndromes but can also result from isolated lacrimal gland agenesis. Congenital alacrima should be evaluated in the differential diagnosis for pediatric patients presenting with symptoms of dry eyes, especially in cases without xerostomia or other systemic rheumatologic findings. Following a thorough history and examination, noninvasive imaging techniques can be utilized to assess for potential lacrimal gland agenesis and aid in confirming the diagnosis.

Craniofacial developmental biology in the single-cell era

The evolution of a unique craniofacial complex in vertebrates made possible new ways of breathing, eating, communicating and sensing the environment. The head and face develop through interactions of all three germ layers, the endoderm, ectoderm and mesoderm, as well as the so-called fourth germ layer, the cranial neural crest. Over a century of experimental embryology and genetics have revealed an incredible diversity of cell types derived from each germ layer, signaling pathways and genes that coordinate craniofacial development, and how changes to these underlie human disease and vertebrate evolution. Yet for many diseases and congenital anomalies, we have an incomplete picture of the causative genomic changes, in particular how alterations to the non-coding genome might affect craniofacial gene expression. Emerging genomics and single-cell technologies provide an opportunity to obtain a more holistic view of the genes and gene regulatory elements orchestrating craniofacial development across vertebrates. These single-cell studies generate novel hypotheses that can be experimentally validated in vivo. In this Review, we highlight recent advances in single-cell studies of diverse craniofacial structures, as well as potential pitfalls and the need for extensive in vivo validation. We discuss how these studies inform the developmental sources and regulation of head structures, bringing new insights into the etiology of structural birth anomalies that affect the vertebrate head.

Molecular and Cellular Regulations in the Development of the Choroidal Circulation System

Disorders in the development and regulation of blood vessels are involved in various ocular disorders, such as persistent hyperplastic primary vitreous, familial exudative vitreoretinopathy, and choroidal dystrophy. Thus, the appropriate regulation of vascular development is essential for healthy ocular functions. However, regulation of the developing choroidal circulation system has not been well studied compared with vascular regulation in the vitreous and the retina. The choroid is a vascular-rich and uniquely structured tissue supplying oxygen and nutrients to the retina, and hypoplasia and the degeneration of the choroid are involved in many ocular disorders. Therefore, understanding the developing choroidal circulation system expands our knowledge of ocular development and supports our understanding of ocular disorders. In this review, we examine studies on regulating the developing choroidal circulation system at the cellular and molecular levels and discuss the relevance to human diseases.

Ontogeny of the nasolacrimal apparatus and nasal sensory systems of the American alligator (Alligator mississippiensis)

The nasolacrimal apparatus (NLA) is a feature common to many sauropsid amniotes. It consists of an orbital Harderian gland (HG)whose secretions drain into the nasal cavity, in the vicinity of the vomeronasal organ (VNO), an accessory olfactory organ derived from the olfactory epithelium, and a connecting nasolacrimal duct (NLD). Though not all features are present in all posthatchling sauropsids (i.e., no VNO in crocodilomorphs), it is not clear if this system either never existed or failed to develop during the embryonic stages. The purpose of this study is to histologically describe the ontogeny of the NLA and the main olfactory organ in Alligator mississippiensis. Alligator specimens, from embryonic stage 9 to hatchling, were serially histologically sectioned, stained, photographed, and segmented into different tissues using Abobe Photoshop and then reconstructed using Amira for 3D analysis and quantitative nasal epithelial distribution. Though there was no evidence of a VNO, the rest of the NLA was present. The development of the NLA could be subdivided into four phases: (1) inception of NLD, (2) establishment of orbitonasal connections of NLD, (3) bone development, and (4) nasal cavity growth. Glands mature during this last phase and the nasal region rapidly grows, rotates, and is displaced anteriorly. The gradual proportional increase in nonolfactory epithelial distribution during ontogeny is consistent with the literature. Alligator embryonic nasal and NLD growth differs from that of mammals and squamates. The NLD is connected to the anterior third of the nasal region during its initial attachment, but as anterior nasal growth exceeds posterior growth, it is gradually displaced into the posterior third of the nasal region by hatching. It is unknown whether this is a derived archosaur condition or just another example of the morphological variation seen within sauropsid amniotes.

Development of high-throughput lacrimal gland organoid platforms for drug discovery in dry eye disease

Dysfunction and damage of the lacrimal gland (LG) results in ocular discomfort and dry eye disease (DED). Current therapies for DED do not fully replenish the necessary lubrication to rescue optimal vision. New drug discovery for DED has been limited perhaps because in vitro models cannot mimic the biology of the native LG. The existing platforms for LG organoid culture are scarce and still not ready for consistency and scale up production towards drug screening. The magnetic three-dimensional (3D) bioprinting (M3DB) is a novel system for 3D in vitro biofabrication of cellularized tissues using magnetic nanoparticles to bring cells together. M3DB provides a scalable platform for consistent handling of spheroid-like cell cultures facilitating consistent biofabrication of organoids. Previously, we successfully generated innervated secretory epithelial organoids from human dental pulp stem cells with M3DB and found that this platform is feasible for epithelial organoid bioprinting. Research targeting LG organogenesis, drug discovery for DED has extensively used mouse models. However, certain inter-species differences between mouse and human must be considered. Porcine LG appear to have more similarities to human LG than the mouse counterparts. We have conducted preliminary studies with the M3DB for fabricating LG organoids from primary cells isolated from murine and porcine LG, and found that this platform provides robust LG organoids for future potential high-throughput analysis and drug discovery. The LG organoid holds promise to be a functional model of tearing, a platform for drug screening, and may offer clinical applications for DED.

Embryonic Development of the Orbit

The embryonic and fetal development of the orbit comprises a series of sequential events, starting with the fertilization of the ovum and extending until birth. Most of the publications dealing with orbital morphogenesis describe the sequential development of each germinal layer, the ectoderm with its neuroectoderm derivative and the mesoderm. This approach provides a clear understanding of the mode of development of each layer but does not give the reader a general picture of the structure of the orbit within any specified time frame. In order to enhance our understanding of the developmental anatomy of the orbit, the authors have summarized the recent developments in orbital morphogenesis, a temporally precise and morphogenetically intricate process. Understanding this multidimensional process of development in prenatal life, identifying and linking signaling cascades, as well as the regulatory genes linked to existing diseases, may pave the way for advanced molecular diagnostic testing, developing minimally invasive interventions, and the use of progenitor/stem cell and even regenerative therapy.

Fetal Development of the Orbit

Human prenatal development is divided into an embryonic period and a fetal period. Intense organogenetic activity occurs in the embryonic period of prenatal life, while the fetal period is marked by less intense changes. Knowledge of the embryology of the orbit not only allows insights into how normal variations in the orbital structure arise but also provides an understanding of how congenital deformities occur when normal orbital development goes awry. In order to explore our understanding of the developmental anatomy of the orbit during the fetal period of prenatal life, the authors have summarized the major milestones in orbital morphogenesis, a temporally precise and morphogenetically intricate process. This process can be considered as an anatomic series of complex, well-orchestrated changes in morphology as well as a series of complex biochemical and molecular events that coordinate and control the anatomic development. Identifying and linking signaling pathways and regulatory genes linked with normal orbital morphogenesis is a crucial step to offer patients with chronic or incurable orbital diseases effective treatment options in the future.

The crucial role of model systems in understanding the complexity of cell signaling in human neurocristopathies

Animal models are useful to study the molecular, cellular, and morphogenetic mechanisms underlying normal and pathological development. Cell-based study models have emerged as an alternative approach to study many aspects of human embryonic development and disease. The neural crest (NC) is a transient, multipotent, and migratory embryonic cell population that generates a diverse group of cell types that arises during vertebrate development. The abnormal formation or development of the NC results in neurocristopathies (NCPs), which are characterized by a broad spectrum of functional and morphological alterations. The impaired molecular mechanisms that give rise to these multiphenotypic diseases are not entirely clear yet. This fact, added to the high incidence of these disorders in the newborn population, has led to the development of systematic approaches for their understanding. In this article, we have systematically reviewed the ways in which experimentation with different animal and cell model systems has improved our knowledge of NCPs, and how these advances might contribute to the development of better diagnostic and therapeutic tools for the treatment of these pathologies. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Stem Cells and Development Congenital Diseases > Molecular and Cellular Physiology Neurological Diseases > Genetics/Genomics/Epigenetics.

Ultrasonographic Subclinical Signs of Inflammation of the Lacrimal, Parotid, and Submandibular Glands in Users of Cosmetic Fillers

OBJECTIVES

To detect ultrasonographic inflammatory signs in the lacrimal, parotid, and submandibular glands in cosmetic fillers (CFs) users.

METHODS

A prospective and cross-sectional ultrasound study of the glands in cases with CFs was performed. The sample included users of hyaluronic acid, silicone oil, polymethylmethacrylate, polycaprolactone, calcium hydroxyapatite, and polyacrylamide. Abnormalities of the parenchyma and hypervascularity signs of the glands were compared with a control group (n = 10), evaluated by 2 observers, and correlated with the type, number, and location of the facial CFs. Cohen's kappa test and logistic regression models with odds ratios (OR) adjusted by age with 95% CI were performed.

RESULTS

Sixty-three patients with CFs met the criteria. Parotid and submandibular glands had the highest percentage of parenchymal involvement: 87.3 and 88.9%, respectively (p <.01). Abnormalities of the echostructure of the parenchyma and hypervascularity of the glands were detected with all kinds of fillers without significant differences per type. A significant substantial interrater kappa (0.61) with an agreement of 90% for all glands among observers was found.

CONCLUSION

Users of common types of CFs frequently present subclinical ultrasonographic signs of inflammation of the lacrimal, parotid, and submandibular glands. Further research on the topic seems necessary.

Lacrimal gland choristomas

The purpose of this article was to report a case of intraconal lacrimal gland tissue and to review the literature on lacrimal gland choristoma. The magnetic resonance imaging findings of a biopsy-proven orbital case are also presented. A PubMed database search was performed using the key terms heterotopic, ectopic, aberrant, choristoma, and lacrimal gland to identify all the previously documented studies on lacrimal gland choristoma, in English, Spanish, and French. We classified the lacrimal gland choristoma cases classified according to the location of the lesions, clinical appearance, management, and outcome. The search targeting the period between 1887 and 2019 returned 79 articles, which were reviewed. We found a total of 113 cases of choristomas with normal lacrimal gland tissue. Only two of them were not associated with the eye or its adnexa while the remaining 111 lesions were found either on the ocular surface (n=46) or in the orbit (n=34). Intraocular choristomas were found in 18 patients, and the rest of the lesions were noted either on the eyelids (n=10) or in the lacrimal drainage system (n=3). Orbital and intraocular choristomas are the most harmful lesions as orbital choristomas are frequently associated with permanent diplopia while intraocular lacrimal gland choristomas have a poor visual prognosis and are a common cause of enucleation of the eye. In one of the reported cases, a corneal lacrimal gland choristoma had been experimentally induced by activating the FGF10 signaling pathway. Lacrimal gland choristomas are not uncommon. This peculiar type of lesion has been experimentally induced and may appear in a variety of locations associated with the globe and its adnexa.

Congenital alacrima

The congenital absence of tear production or alacrima is a distinctively unusual clinical sign that harbors a wide variety of etiologies. While alacrima can be only isolated to the lacrimal system, it is more often associated with progressive multisystem involvement from underlying genetic disorders. Recognizing the subtle ocular signs in these diseases will promote a timely diagnosis and management before potential life-threatening consequences occur. Hence, the current article will review the ophthalmological findings, systemic manifestations, genetic associations, and differential diagnosis of congenital alacrima.

The role of teratogens in neural crest development

The neural crest (NC), discovered by Wilhelm His 150 years ago, gives rise to a multipotent migratory embryonic cell population that generates a remarkably diverse and important array of cell types during the development of the vertebrate embryo. These cells originate in the neural plate border (NPB), which is the ectoderm between the neural plate and the epidermis. They give rise to the neurons and glia of the peripheral nervous system, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies are a class of congenital diseases resulting from the abnormal induction, specification, migration, differentiation or death of NC cells (NCCs) during embryonic development and have an important medical and societal impact. In general, congenital defects affect an appreciable percentage of newborns worldwide. Some of these defects are caused by teratogens, which are agents that negatively impact the formation of tissues and organs during development. In this review, we will discuss the teratogens linked to the development of many birth defects, with a strong focus on those that specifically affect the development of the NC, thereby producing neurocristopathies. Although increasing attention is being paid to the effect of teratogens on embryonic development in general, there is a strong need to critically evaluate the specific role of these agents in NC development. Therefore, increased understanding of the role of these factors in NC development will contribute to the planning of strategies aimed at the prevention and treatment of human neurocristopathies, whose etiology was previously not considered.

Levels of oligomeric α-Synuclein in reflex tears distinguish Parkinson's disease patients from healthy controls

Aim: Due to active engagement of sensory and afferent nerve fibers in reflex tearing which could be affected in Parkinson's disease (PD), we tested reflex tears as a source of potential PD biomarkers. Patients & methods: Reflex tears collected from 84 PD and 84 age- and sex-equivalent healthy controls (HC) were used to measure levels of oligomeric α-Syn (α-Syn_Oligo), total α-Syn (α-Syn_Total), CCL2, DJ-1, lactoferrin and MMP9. Results: α-syn_Oligo (p < 0.0001), CCL2 (p = 0.003) and lactoferrin (p = 0.002) were significantly elevated in PD patient tears relative to HC tears. Tear flow was significantly lower in PD relative to HC (p = 0.001). Conclusion: Reflex tears are a potential source for detection of characteristic changes in PD patients.

Initial stages of development of the submandibular gland (human embryos at 5.5-8 weeks of development)

The aim of this study was to determine the main stages of submandibular salivary gland development during the embryonic period in humans. In addition, we studied submandibular salivary gland development in rats on embryonic days 14-16 and expression in the submandibular salivary gland region with the monoclonal antibody HNK-1. Serial sections from 25 human embryos with a greatest length ranging from 10 to 31 mm (Carnegie stages 16-23; weeks 5.5-8 of development) and Wistar rats of embryonic days (E) 14-16 were analysed with light microscopy. Five stages of submandibular salivary gland development were identified. The prospective stage (1), between weeks 5.5 and early week 6, is characterized by a thickening of the epithelium of the medial paralingual groove in the floor of the mouth corresponding to the primordium of the submandibular salivary gland parenchyma. At this stage, the primordium of the parasympathetic ganglion lies below the lingual nerve. The primordium of the submandibular salivary gland parenchyma is observed in rats on E14 in the medial paralingual groove with mesenchymal cells, underlying the lingual nerve. These cells are HNK-1-positive, corresponding to the primordium of the parasympathetic ganglion. The bud stage (2), at the end of week 6 in humans and on E15 in rats, is characterized by the proliferation and invagination of the epithelial condensation, surrounded by an important condensation of the mesenchyme. The pseudoglandular stage (3) at week 6.5 is characterized by the beginning of the formation of lobes in the condensed mesenchyme. The canalicular stage (4), between week 7 and 7.5, is characterized by the appearance of a lumen in the proximal part of the submandibular duct. The innervation stage (5) occurs during week 8, with the innervation of the submandibular and interlobular ducts. Nervous branches arriving from the parasympathetic ganglion innervate the glandular parenchyma. Numerous blood vessels are observed nearby. Our results suggest that submandibular salivary gland development requires interactions among epithelium, mesenchyme, parasympathetic ganglion and blood vessels.

Molecular regulation of ocular gland development

The tear film is produced by two ocular glands, the lacrimal glands, which produce the aqueous component of this film, and the meibomian glands, which secrete the lipidic component that is key to reduce evaporation of the watery film at the surface of the eye. Embryonic development of these exocrine glands has been mostly studied in mice, which also develop Harderian glands, a third type of ocular gland whose role is still not well understood. This review provides an update on the signalling pathways, transcription factors andextracellular matrix components that have been shown to play a role in ocular gland development.

Embryologic and Fetal Development of the Human Orbit

PURPOSE

To review the recent data about orbital development and sort out the controversies from the very early stages during embryonic life till final maturation of the orbit late in fetal life, and to appreciate the morphogenesis of all the definitive structures in the orbit in a methodical and timely fashion.

METHODS

The authors extensively review major studies detailing every aspect of human embryologic and fetal orbital morphogenesis including the development of extraocular muscles, orbital fat, vessels, nerves, and the supportive connective tissue framework as well as bone. These interdisciplinary studies span almost a century and a half, and include some significant controversial opposing points of view which the authors hopefully sort out. The authors also highlight a few of the most noteworthy molecular biologic studies regarding the multiple and interacting signaling pathways involved in regulating normal orbital morphogenesis.

RESULTS

Orbital morphogenesis involves a successive series of subtle yet tightly regulated morphogenetic events that could only be explained through the chronological narrative used by the authors. The processes that trigger and contribute to the formation of the orbits are complex and seem to be intricately regulated by multifaceted interactions and bidirectional cross-talk between a multitude of cellular building raw materials including the developing optic vesicles, neuroectoderm, cranial neural crest cells and mesoderm.

CONCLUSIONS

Development of the orbit is a collective enterprise necessitating interactions between, as well as contributions from different cell populations both within and beyond the realm of the orbit. A basic understanding of the processes underlying orbital ontogenesis is a crucial first step toward establishing a genetic basis or an embryologic link with orbital disease.

Pbx loss in cranial neural crest, unlike in epithelium, results in cleft palate only and a broader midface

Orofacial clefting represents the most common craniofacial birth defect. Cleft lip with or without cleft palate (CL/P) is genetically distinct from cleft palate only (CPO). Numerous transcription factors (TFs) regulate normal development of the midface, comprising the premaxilla, maxilla and palatine bones, through control of basic cellular behaviors. Within the Pbx family of genes encoding Three Amino-acid Loop Extension (TALE) homeodomain-containing TFs, we previously established that in the mouse, Pbx1 plays a preeminent role in midfacial morphogenesis, and Pbx2 and Pbx3 execute collaborative functions in domains of coexpression. We also reported that Pbx1 loss from cephalic epithelial domains, on a Pbx2- or Pbx3-deficient background, results in CL/P via disruption of a regulatory network that controls apoptosis at the seam of frontonasal and maxillary process fusion. Conversely, Pbx1 loss in cranial neural crest cell (CNCC)-derived mesenchyme on a Pbx2-deficient background results in CPO, a phenotype not yet characterized. In this study, we provide in-depth analysis of PBX1 and PBX2 protein localization from early stages of midfacial morphogenesis throughout development of the secondary palate. We further establish CNCC-specific roles of PBX TFs and describe the developmental abnormalities resulting from their loss in the murine embryonic secondary palate. Additionally, we compare and contrast the phenotypes arising from PBX1 loss in CNCC with those caused by its loss in the epithelium and show that CNCC-specific Pbx1 deletion affects only later secondary palate morphogenesis. Moreover, CNCC mutants exhibit perturbed rostro-caudal organization and broadening of the midfacial complex. Proliferation defects are pronounced in CNCC mutants at gestational day (E)12.5, suggesting altered proliferation of mutant palatal progenitor cells, consistent with roles of PBX factors in maintaining progenitor cell state. Although the craniofacial skeletal abnormalities in CNCC mutants do not result from overt patterning defects, osteogenesis is delayed, underscoring a critical role of PBX factors in CNCC morphogenesis and differentiation. Overall, the characterization of tissue-specific Pbx loss-of-function mouse models with orofacial clefting establishes these strains as unique tools to further dissect the complexities of this congenital craniofacial malformation. This study closely links PBX TALE homeodomain proteins to the variation in maxillary shape and size that occurs in pathological settings and during evolution of midfacial morphology.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

Isolated bilateral congenital lacrimal gland agenesis - Report of two cases

Congenital lacrimal gland agenesis, also called congenital alacrima, is a rare cause of dry eye and is characterized by aplasia or hypoplasia of lacrimal glands. We present two 5-year old children with congenital lacrimal gland agenesis. The two cases had the final diagnosis of isolated bilateral congenital lacrimal gland agenesis and we document the clinical aspects, treatment and present a literature review related to this rare condition.

Lacrimal gland development: From signaling interactions to regenerative medicine

The lacrimal gland plays a pivotal role in keeping the ocular surface lubricated, and protecting it from environmental exposure and insult. Dysfunction of the lacrimal gland results in deficiency of the aqueous component of the tear film, which can cause dryness of the ocular surface, also known as the aqueous-deficient dry eye disease. Left untreated, this disease can lead to significant morbidity, including frequent eye infections, corneal ulcerations, and vision loss. Current therapies do not treat the underlying deficiency of the lacrimal gland, but merely provide symptomatic relief. To develop more sustainable and physiological therapies, such as in vivo lacrimal gland regeneration or bioengineered lacrimal gland implants, a thorough understanding of lacrimal gland development at the molecular level is of paramount importance. Based on the structural and functional similarities between rodent and human eye development, extensive studies have been undertaken to investigate the signaling and transcriptional mechanisms of lacrimal gland development using mouse as a model system. In this review, we describe the current understanding of the extrinsic signaling interactions and the intrinsic transcriptional network governing lacrimal gland morphogenesis, as well as recent advances in the field of regenerative medicine aimed at treating dry eye disease. Developmental Dynamics 246:970-980, 2017. © 2017 Wiley Periodicals, Inc.

RNA-Seq and CyTOF immuno-profiling of regenerating lacrimal glands identifies a novel subset of cells expressing muscle-related proteins

The purpose of the present studies was to use CyTOF and RNA-Seq technologies to identify cells and genes involved in lacrimal gland repair that could be targeted to treat diseases of lacrimal gland dysfunction. Lacrimal glands of female BALB/c mice were experimentally injured by intra-glandular injection of interleukin 1 alpha (IL-1α). The lacrimal glands were harvested at various time points following injury (1 to 14 days) and used to either prepare single cell suspensions for CyTOF immuno-phenotyping analyses or to extract RNA for gene expression studies using RNA-Seq. CyTOF immuno-phenotyping identified monocytes and neutrophils as the major infiltrating populations 1 and 2 days post injury. Clustering of significantly differentially expressed genes identified 13 distinct molecular signatures: 3 associated with immune/inflammatory processes included genes up-regulated at days 1–2 and 3 associated with reparative processes with genes up-regulated primarily between days 4 and 5. Finally, clustering identified 65 genes which were specifically up-regulated 2 days post injury which was enriched for muscle specific genes. The expression of select muscle-related proteins was confirmed by immunohistochemistry which identified a subset of cells expressing these proteins. Double staining experiments showed that these cells are distinct from the myoepithelial cells. We conclude that experimentally induced injury to the lacrimal gland leads to massive infiltration by neutrophils and monocytes which resolved after 3 days. RNAseq and immunohistochemistry identified a group of cells, other than myoepithelial cells, that express muscle-related proteins that could play an important role in lacrimal gland repair.

Defining epithelial cell dynamics and lineage relationships in the developing lacrimal gland

The tear-producing lacrimal gland is a tubular organ that protects and lubricates the ocular surface. The lacrimal gland possesses many features that make it an excellent model in which to investigate tubulogenesis, but the cell types and lineage relationships that drive lacrimal gland formation are unclear. Using single-cell sequencing and other molecular tools, we reveal novel cell identities and epithelial lineage dynamics that underlie lacrimal gland development. We show that the lacrimal gland from its earliest developmental stages is composed of multiple subpopulations of immune, epithelial and mesenchymal cell lineages. The epithelial lineage exhibits the most substantial cellular changes, transitioning through a series of unique transcriptional states to become terminally differentiated acinar, ductal and myoepithelial cells. Furthermore, lineage tracing in postnatal and adult glands provides the first direct evidence of unipotent KRT5⁺ epithelial cells in the lacrimal gland. Finally, we show conservation of developmental markers between the developing mouse and human lacrimal gland, supporting the use of mice to understand human development. Together, our data reveal crucial features of lacrimal gland development that have broad implications for understanding epithelial organogenesis.

Tadpole-shaped lateralized parietal atretic cephalocele associated with an ipsilateral lacrimal gland fistula and schizencephalic clefts

BACKGROUND

Parietal atretic cephalocele (AC) and its associated intracranial venous anomalies, such as vertical embryonic positioning of the straight sinus (VEP of SS), have, in previous reports, been exclusively restricted to the midline.

CLINICAL PRESENTATION

We report a patient with lateralized parietal AC on the right side. The AC was in the shape of a tadpole, with a large head and a long tail, extending to the proximity of the right external canthus, where a lacrimal gland fistula was observed. The superior sagittal sinus and VEP of SS were also displaced to the right side, although the sagittal suture was located at the midline. Schizencephalic clefts in the right posterior cortex were also observed.

CONCLUSION

The parietal AC, which was initially located in the midline, could conceivably have been displaced to the right side by other developmental processes. However, the relationship between lateralized AC and associated multiple anomalies on the ipsilateral side is difficult to explain monogenetically. Our case study indicates that AC might have a broader spectrum of clinical symptoms than was once thought to be the case.

Human Lacrimal Gland Gene Expression

BACKGROUND

The study of human lacrimal gland biology and development is limited. Lacrimal gland tissue is damaged or poorly functional in a number of disease states including dry eye disease. Development of cell based therapies for lacrimal gland diseases requires a better understanding of the gene expression and signaling pathways in lacrimal gland. Differential gene expression analysis between lacrimal gland and other embryologically similar tissues may be helpful in furthering our understanding of lacrimal gland development.

METHODS

We performed global gene expression analysis of human lacrimal gland tissue using Affymetrix ® gene expression arrays. Primary data from our laboratory was compared with datasets available in the NLM GEO database for other surface ectodermal tissues including salivary gland, skin, conjunctiva and corneal epithelium.

RESULTS

The analysis revealed statistically significant difference in the gene expression of lacrimal gland tissue compared to other ectodermal tissues. The lacrimal gland specific, cell surface secretory protein encoding genes and critical signaling pathways which distinguish lacrimal gland from other ectodermal tissues are described.

CONCLUSIONS

Differential gene expression in human lacrimal gland compared with other ectodermal tissue types revealed interesting patterns which may serve as the basis for future studies in directed differentiation among other areas.

Unilateral Congenital Lacrimal Gland Agenesis With Contralateral Lacrimal Gland Hypoplasia

Congenital alacrima is a form of primary lacrimal deficiency characterized by aplasia or hypoplasia of the lacrimal gland. The puncta and salivary glands may also be aplastic. The case of a 5-year-old girl with congenital alacrima secondary to lacrimal gland agenesis and hypoplasia without punctal or salivary gland involvement and without other systemic comorbidities is reported.

Myoepithelial Cells: Their Origin and Function in Lacrimal Gland Morphogenesis, Homeostasis, and Repair

Lacrimal gland (LG) is an exocrine tubuloacinar gland that secretes the aqueous layer of the tear film. LG epithelium is composed of ductal, acinar, and myoepithelial cells (MECs) bordering the basal lamina and separating the epithelial layer from the extracellular matrix. Mature MECs have contractile ability and morphologically resemble smooth muscle cells; however, they exhibit features typical for epithelial cells, such as the presence of specific cytokeratin filaments. Increasing evidence supports the assertion that myoepithelial cells (MECs) play key roles in the lacrimal gland development, homeostasis, and stabilizing the normal structure and polarity of LG secretory acini. MECs take part in the formation of extracellular matrix gland and participate in signal exchange between epithelium and stroma. MECs have a high level of plasticity and are able to differentiate into several cell lineages. Here, we provide a review on some of the MEC characteristics and their role in LG morphogenesis, maintenance, and repair.

Development of the nasolacrimal apparatus in the Mongolian gerbil (Meriones unguiculatus), with notes on network topology and function

The nasolacrimal apparatus (NLA) is a multicomponent functional system comprised of multiple orbital glands (up to four larger multicellular exocrine structures), a nasal chemosensory structure (vomeronasal organ: VNO), and a connecting duct (nasolacrimal duct: NLD). Although this system has been described in all tetrapod vertebrate lineages, albeit not always with all three main components present, considerably less is known about its ontogeny. The Mongolian gerbil (Meriones unguiculatus) is a common lab rodent in which the individual components of the adult NLA have been well studied, but as yet nothing is known about the ontogeny of the NLA. In this study, serial sections of 15 fetal and three adult Mongolian gerbil heads show that the development of the NLA falls into three fetal stages: inception (origin of all features), elongation (lengthening of all features), and expansion (widening of all features). No postnatal or juvenile specimens were observed in this study, but considerable growth evidently occurs before the final adult condition is reached. The development of the orbital glands and the VNO in the Mongolian gerbil is largely consistent with those in other mammals, despite a slight nomenclatural conundrum for the anterior orbital glands. However, the Mongolian gerbil NLD follows a more circuitous route than in other tetrapods, due mainly to the convoluted arrangement of the narial cartilages, the development of a pair of enlarged incisors as well as an enlarged infraorbital foramen. The impact of these associated features on the ontogeny and phylogeny of the NLA could be examined through the approach of network science. This approach allows for the incorporation of adaptations to specific lifestyles as potential explanations for the variation observed in the NLA across different tetrapod clades.

[Ocular surface system integrity]

The interplay of different structures belonging to either the anterior segment of the eye or its accessory visual apparatus, which all share common embryological, anatomical, functional, and physiological features, is discussed. Explanation of such terms, as ocular surface, lacrimal functional unit, and ocular surface system, is provided.

Isolation and propagation of mesenchymal stem cells from the lacrimal gland

PURPOSE

Previously, it was reported that the murine lacrimal gland is capable of repair after experimentally induced injury and that the number of stem/progenitor cells was increased during the repair phase (2-3 days after injury). The aim of the present study was to determine whether these cells can be isolated from the lacrimal gland and propagated in vitro.

METHODS

Lacrimal gland injury was induced by injection of interleukin (IL)-1, and injection of saline vehicle served as control. Two and half days after injection, the lacrimal glands were removed and used to prepare explants or acinar cells for tissue culture. Cells derived from the explants and the acinar cells were grown in DMEM supplemented with 10% fetal bovine serum. Cells were stained for the stem cells markers, nestin, vimentin, ABCG2, and Sca-1. Cell proliferation was measured using an antibody against Ki67 or a cell-counting kit. The adipogenic capability of these cells was also tested in vitro.

RESULTS

Results show that nestin-positive cells can be isolated from IL-1-injected, but not saline-injected, lacrimal glands. A population of nestin-positive cells was also positive for vimentin, an intermediate filament protein expressed by mesenchymal cells. In addition, cultured cells expressed two other markers of stem cells, ABCG2 and Sca-1. These cells proliferated in vitro and can be induced to form adipocytes, attesting to their mesenchymal stem cell property.

CONCLUSIONS

Murine lacrimal glands contain mesenchymal stem cells that seem to play a pivotal role in tissue repair.

Mechanisms involved in injury and repair of the murine lacrimal gland: role of programmed cell death and mesenchymal stem cells

The non-keratinized epithelia of the ocular surface are constantly challenged by environmental insults, such as smoke, dust, and airborne pathogens. Tears are the sole physical protective barrier for the ocular surface. Production of tears in inadequate quantity or of inadequate quality results in constant irritation of the ocular surface, leading to dry eye disease, also referred to as keratoconjunctivitis sicca (KCS). Inflammation of the lacrimal gland, such as occurs in Sjogren syndrome, sarcoidosis, chronic graft-versus-host disease, and other pathological conditions, results in inadequate secretion of the aqueous layer of the tear film and is a leading cause of dry eye disease. The hallmarks of lacrimal gland inflammation are the presence of immune cell infiltrates, loss of acinar epithelial cells (the secreting cells), and increased production of proinflammatory cytokines. To date, the mechanisms leading to acinar cell loss and the associated decline in lacrimal gland secretion are still poorly understood. It is also not understood why the remaining lacrimal gland cells are unable to proliferate in order to regenerate a functioning lacrimal gland. This article reviews recent advances in exocrine tissue injury and repair, with emphasis on the roles of programmed cell death and stem/progenitor cells.

Morphogenesis of the human excretory lacrimal system

The aim of this study was to determine the principal developmental stages in the formation of the excretory lacrimal system in humans and to establish its morphogenetic period. The study was performed using light microscopy on serial sections of 51 human specimens: 33 embryos and 18 fetuses ranging from 8 to 137 mm crown-rump length (CR; 5-16 weeks of development). Three stages were identified in the morphogenesis of the excretory lacrimal system: (1) the formative stage of the lacrimal lamina (Carnegie stages 16-18); (2) the formative stage of the lacrimal cord (Carnegie stages 19-23); and (3) the maturative stage of the excretory lacrimal system, from the 9th week of development onward. A three-dimensional reconstruction of the excretory lacrimal system was performed from serial sections of an embryo at the end of the embryonic period (27 mm CR).