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The lacrimal gland (LG) is a tubuloacinar exocrine gland composed of acinar, ductal, and myoepithelial cells. Three-dimensional distribution of acinar lobules, ducts, and myoepithelial cells is necessary for the effective functioning of the organ. LG is the main organ of immune surveillance of the ocular surface system. The embryogenesis of the gland is regulated by the interaction of genetic mechanisms, internal epigenetic (enzyme systems, hormones) and exogenous factors. There is no doubt that there is a clear genetic program for the implementation of the complex process of embryonic development. The mechanisms regulating LG organogenesis initiate the work of a huge number of structural oncogenes, transcription and growth factors, etc. Studying the expression and selective activity of regulatory genes during organ development, their participation in the differentiation of different cell types is a current trend at the nexus of clinical genetics, molecular biology, embryology and immunocytochemistry. Due to its relatively simple structure and accessibility, human LG is a suitable object for potential application in regenerative medicine. Development of a universal protocol for obtaining functional differentiated secretory epithelium of LG capable of expressing tissue-specific markers is an urgent task. Determining the nature and origin of stem cells and progenitor cells will allow the isolation and multiplication of these cells in culture. After obtaining a functionally active culture of LG cells, it is possible to create a model of autoimmune diseases.

Background: Arrhinia is defined as the partial or complete absence of the nasal structures. It is a defect of embryonal origin and can be seen in association with other craniofacial anomalies, central nervous system anomalies, absence of paranasal sinuses, and other palatal and ocular abnormalities. Very few patients with arrhinia have been reported so far in the history of modern medicine., Case Report: This study reports an adult patient with congenital partial arrhinia and reviews the literature along with the embryological basis of such a rare disease., Conclusion: Arrhinia is a medical condition with scarce documentation in the literature. This article presents the clinical as well as radiological features of this rare entity.

A lack of ectodysplasin-A (Eda) signaling leads to dry eye symptoms, which have so far only been associated with altered Meibomian glands. Here, we used loss-of-function ( Eda -/- ) mutant mice to unravel the impact of Eda signaling on lacrimal gland formation, maturation and subsequent physiological function. Our study demonstrates that Eda activity is dispensable during lacrimal gland embryonic development. However, using a transcriptomic approach, we show that the Eda pathway is necessary for proper cell terminal differentiation in lacrimal gland epithelium and correlated with modified expression of secreted factors commonly found in the tear film. Finally, we discovered that lacrimal glands present a bilateral reduction of Eda signaling activity in response to unilateral corneal injury. This observation hints towards a role for the Eda pathway in controlling the switch from basal to reflex tears, to support corneal wound healing. Collectively, our data suggest a crucial implication of Eda signaling in the cornea-lacrimal gland feedback loop, both in physiological and pathophysiological conditions. Our findings demonstrate that Eda downstream targets could help alleviate dry eye symptoms., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2019. Published by The Company of Biologists Ltd.)

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., (Copyright © 2018. Published by Elsevier Ltd.)

Punctal agenesis is defined as the absence of the punctum occurring secondary to a failure of embryogenesis. This review synthesizes existing data on the embryology, anatomy, clinical presentation, symptomatology, management options and treatment outcomes of punctal agenesis. A foundational knowledge of the underlying embryologic and anatomical abnormalities is fundamental to understanding its clinical presentation and assists in choosing an appropriate management strategy. Existing outcomes data is generally favorable and suggests management with a step-wise approach can alleviate symptoms in patients across a spectrum of disease., (Copyright © 2019 Elsevier GmbH. All rights reserved.)

Although single-cell RNA sequencing (scRNA-seq) has become one of the most powerful methods available for transcriptome analysis, the quality of scRNA-seq data largely depends on cell preparation. Cell preparation from cultured cells and tissues requires different methods because of the inherent differences between these two categories of cells. Compared to cultured cells, tissues have more extracellular matrix, and the cells are generally more adherent and thus difficult to dissociate. The challenge is to achieve sufficient dissociation, cell counts, and viability all at the same time. This protocol describes approaches that help achieve these goals. These include a cold dissociation technique using cryophilic proteases active at cold temperature, timing of trituration during protease digestion, as well as filtration and washing methods that optimize cell viability and retention. Materials and equipment that optimize the process also discussed. © 2019 by John Wiley & Sons, Inc., (© 2019 John Wiley & Sons, Inc.)

The lacrimal gland (LG) is important as it has a significant role in maintaining the stability of the microenvironment of the ocular surface. When a loss of function occurs in the LG, a significant reduction in tear production and dry eye disease (DED) may occur. A mammalian LG is a secretory gland consisting of acini and ducts. The interaction between epithelial cells and mesenchymal cells plays a major role during development and the self-restoration process of the gland. Some factors, such as fibroblast growth factor 10 and bone morphogenetic protein 7, are associated with these processes. Though several strategies for LG regeneration have been established, there is still a long way to go before there is clarity about LG stem cells. In this review, current knowledge on LG development, LG self-repair, DED and correlative regeneration therapies are summarized.

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., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

The tear film protects the terrestrial animal's ocular surface and the lacrimal gland provides important aqueous secretions necessary for its maintenance. Despite the importance of the lacrimal gland in ocular health, molecular aspects of its development remain poorly understood. We have identified a noncoding RNA (miR-205) as an important gene for lacrimal gland development. Mice lacking miR-205 fail to properly develop lacrimal glands, establishing this noncoding RNA as a key regulator of lacrimal gland development. Specifically, more than half of knockout lacrimal glands never initiated, suggesting a critical role of miR-205 at the earliest stages of lacrimal gland development. RNA-seq analysis uncovered several up-regulated miR-205 targets that may interfere with signaling to impair lacrimal gland initiation. Supporting this data, combinatorial epistatic deletion of Fgf10, the driver of lacrimal gland initiation, and miR-205 in mice exacerbates the lacrimal gland phenotype. We develop a molecular rheostat model where miR-205 modulates signaling pathways related to Fgf10 in order to regulate glandular development. These data show that a single microRNA is a key regulator for early lacrimal gland development in mice and highlights the important role of microRNAs during organogenesis., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The aim of the present study was morphological and histochemical analysis of the lacrimalgland (LG) in African black ostrich Struthio camelus domesticus in the embryonic and postnatalperiod. Studies were conducted on 50 ostriches aged between the 28th day of incubation until7 months old. Tissue sections were stained with haematoxylin and eosin, Azan trichrome,periodic acid-Schiff, Alcian blue pH 2.5, aldehyde fuchsin and Hale's dialysed iron. The LGin ostrich was classified as a tubulo-acinar type. The primordia of the lobes were determinedin the LG structure on the 28th day of incubation, whilst the weakly visible lobes with aciniand tubules were observed on the 40th day of incubation. Morphometric studies of the LGshowed steady growth, characterised by an increase in both length and width. Histometricmeasurements of lobe size showed little difference between the first, second and third agegroups, whilst in the fourth age group a marked increase in size of lobes was observed.The study showed that, apart from morphological changes, during the growth of the LGthe character of acid mucopolysaccharides changed. Sulphated acid mucopolysaccharideswere indicated, particularly with aldehyde fuchsin (AF) staining in the fourth age group.The Hale's dialysed iron (HDI) staining showed a low concentration of carboxylated acidmucopolysaccharides in the first and second age groups and a higher concentration in thethird and fourth age groups. Periodic acid-Schiff staining (PAS)-positive cells were observedin each age group, but only a small number of cells with a weakly PAS-positive reaction weredemonstrated in the first age group.

Murine lacrimal, harderian and meibomian glands develop from the prospective conjunctival and eyelid epithelia and produce secretions that lubricate and protect the ocular surface. Sox9 expression localizes to the presumptive conjunctival epithelium as early as E11.5 and is detected in the lacrimal and harderian glands as they form. Conditional deletion showed that Sox9 is required for the development of the lacrimal and harderian glands and contributes to the formation of the meibomian glands. Sox9 regulates the expression of Sox10 to promote the formation of secretory acinar lobes in the lacrimal gland. Sox9 and FGF signaling were required for the expression of cartilage-associated extracellular matrix components during early stage lacrimal gland development. Fgfr2 deletion in the ocular surface epithelium reduced Sox9 and eliminated Sox10 expression. Sox9 deletion from the ectoderm did not affect Fgf10 expression in the adjacent mesenchyme or Fgfr2 expression in the epithelium, but appeared to reduce FGF signaling. Sox9 heterozygotes showed a haploinsufficient phenotype, in which the exorbital branch of the lacrimal gland was absent in most cases. However, enhancement of epithelial FGF signaling by expression of a constitutively active FGF receptor only partially rescued the lacrimal gland defects in Sox9 heterozygotes, suggesting a crucial role of Sox9, downstream of FGF signaling, in regulating lacrimal gland branching and differentiation., (© 2014. Published by The Company of Biologists Ltd.)

Purpose: Smad4, a key intracellular mediator in TGF-β signaling, plays a critical role in the normal development of many tissues/organs. However, its functional role in the development of the lacrimal gland (LG) has never been reported. The aim of this study was to investigate the role Smad4 may play in the development of LG by using Smad4 conditional knockout mice and comparing their LG changes with the LG in normal control mice., Methods: Smad4 in the LG, as well as in the lens, cornea, and ectoderm of the eyelids, was conditionally inactivated by using Pax6 promoter-driven Cre-transgenic mice. Lac Z reporter was used to visualize the developing LG by X-gal staining, and standard histologic approaches were used to reveal morphologic alterations., Results: Inactivation of Smad4 resulted in reduction in the size and number of acini in the embryonic LG and in pigment accumulation within the LG, although it did not affect the formation of the primary lacrimal bud. After birth, the LG from Smad4-mutant mice developed slowly, and pigment was observed starting from the P7 mutant LG. Thereafter, the mutant LG was considerably smaller than the normal LG and was eventually replaced by adipose tissue., Conclusions: These results support the notion that Smad4 is essential for the normal development and maintenance of the mouse LG.

Purpose: Lacrimal gland (LG) morphogenesis and repair are regulated by a complex interplay of intrinsic factors (e.g., transcription factors) and extrinsic signals (e.g., soluble growth/signaling factors). Many of these interconnections remain poorly characterized. Runt-related (Runx) factors belong to a small family of heterodimeric transcription factors known to regulate lineage-specific proliferation and differentiation of stem cells. The purpose of this study was to define the expression pattern and the role of Runx proteins in LG development and regeneration., Methods: Expression of epithelial-restricted transcription factors in murine LG was examined using immunostaining, qRT-PCR, and RT(2)Profiler PCR microarrays. The role of Runx transcription factors in LG morphogenesis was studied using siRNA and ex vivo LG cultures. Expression of Runx transcription factors during LG regeneration was assessed using in vivo model of LG regeneration., Results: We found that Runx factors are expressed in the epithelial compartment of the LG; in particular, Runx1 was restricted to the epithelium with highest level of expression in ductal and centroacinar cells. Downregulation of Runx1 to 3 expression using Runx-specific siRNAs abolished LG growth and branching and our data suggest that Runx1, 2, and 3 are partially redundant in LG development. In siRNA-treated LG, reduction of branching correlated with reduction of epithelial proliferation, as well as expression of cyclin D1 and the putative epithelial progenitor cell marker cytokeratin-5. Runx1, Runx3, and cytokeratin-5 expression increased significantly in regenerating LG and there was modest increase in Runx2 expression during LG differentiation., Conclusions: Runx1 and 2 are new markers of the LG epithelial lineage and Runx factors are important for normal LG morphogenesis and regeneration.

Pax6 is an essential transcription factor for lens, lacrimal gland and pancreas development. Previous transgenic analyses have identified several Pax6 regulatory elements, but their functional significance and binding factors remain largely unknown. In this study, we generated two genomic truncations to delete three elements that were previously shown to bind to the Meis/Prep family homeoproteins. One 3.1 kb deletion (Pax6(∆DP/∆DP)) removed two putative pancreatic enhancers and a previously identified ectodermal enhancer, while a 450 bp sub-deletion (Pax6(∆PE/∆PE)) eliminated only the promoter-proximal pancreatic enhancer. Immunohistochemistry and quantitative RT-PCR showed that the Pax6(∆PE/∆PE) pancreata had a significant decrease in Pax6, glucagon, and insulin expression, while no further reductions were observed in the Pax6(∆DP/∆DP) mice, indicating that only the 450 bp region is required for pancreatic development. In contrast, Pax6(∆DP/∆DP), but not Pax6(∆PE/∆PE) mice, developed stunted lacrimal gland and lens hypoplasia which was significantly more severe than that reported when only the ectodermal enhancer was deleted. This result suggested that the ectodermal enhancer must cooperate with its neighboring sequences to regulate the Pax6 ectodermal expression. Finally, we generated conditional knockouts of Prep1 in the lens and pancreas, but surprisingly, did not observe any developmental defects. Together, these results provide functional evidence for the independent and synergistic roles of the Pax6 upstream enhancers, and they suggest the potential redundancy of Meis/Prep protein in Pax6 regulation., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The lacrimal gland (LG) develops through branching morphogenesis and produces secretions, including tears, that lubricate and protect the ocular surface. Despite the prevalence of LG disorders such as dry eye, relatively little is known about the regulation of LG development. In this study, we show that the homeobox transcription factor Barx2 is highly expressed in conjunctival epithelium, eyelids and ocular [lacrimal, harderian (HG), and meibomian (MG)] glands and is necessary for normal ocular gland and eyelid development. Barx2(-/-) mice show defective LG morphogenesis, absence of the HG, and defects in MG and eyelid fusion. Ex vivo antisense assays confirm the requirement for Barx2 in LG bud elongation and branching. Gene expression profiles reveal decreased expression of several adhesion and matrix remodeling molecules in Barx2(-/-) LGs. In culture, Barx2 regulates expression of matrix metalloproteinases (MMPs) and epithelial cell migration through the extracellular matrix. Fibroblast growth factors are crucial regulators of LG development and we show that Barx2 is required for Fgf10-induced LG bud elongation and that both Barx2 and Fgf10 cooperate in the regulation of MMPs. Together, these data suggest a mechanism for the effects of loss of Barx2 on ocular gland development. Intriguingly, salivary glands that also express a high level of Barx2 develop normally in Barx2(-/-) mice and do not show altered levels of MMPs. Thus, the function of Barx2 is specific to ocular gland development. Based on our data, we propose a functional network involving Barx2, Fgf10 and MMPs that plays an essential role in regulating branching morphogenesis of the ocular glands.

Heparan sulfate, an extensively sulfated glycosaminoglycan abundant on cell surface proteoglycans, regulates intercellular signaling through its binding to various growth factors and receptors. In the lacrimal gland, branching morphogenesis depends on the interaction of heparan sulfate with Fgf10-Fgfr2b. To address if lacrimal gland development and FGF signaling depends on 2-O-sulfation of uronic acids and 6-O-sulfation of glucosamine residues, we genetically ablated heparan sulfate 2-O and 6-O sulfotransferases (Hs2st, Hs6st1, and Hs6st2) in developing lacrimal gland. Using a panel of phage display antibodies, we confirmed that these mutations disrupted 2-O and/or 6-O but not N-sulfation of heparan sulfate. The Hs6st mutants exhibited significant lacrimal gland hypoplasia and a strong genetic interaction with Fgf10, demonstrating the importance of heparan sulfate 6-O sulfation in lacrimal gland FGF signaling. Altering Hs2st caused a much less severe phenotype, but the Hs2st;Hs6st double mutants completely abolished lacrimal gland development, suggesting that both 2-O and 6-O sulfation of heparan sulfate contribute to FGF signaling. Combined Hs2st;Hs6st deficiency synergistically disrupted the formation of Fgf10-Fgfr2b-heparan sulfate complex on the cell surface and prevented lacrimal gland induction by Fgf10 in explant cultures. Importantly, the Hs2st;Hs6st double mutants abrogated FGF downstream ERK signaling. Therefore, Fgf10-Fgfr2b signaling during lacrimal gland development is sensitive to the content or arrangement of O-sulfate groups in heparan sulfate. To our knowledge, this is the first study to show that simultaneous deletion of Hs2st and Hs6st exhibits profound FGF signaling defects in mammalian development.

Background: Bilateral dacryocystoceles develop as a result of obstruction of the nasolacrimal canal. The advances in obstetric sonography have led to increased diagnosis of this structural defect in the antenatal period as early as 24 weeks' gestation., Case: We describe a case of bilateral dacryocystocele with clear visualization of this defect using 3-D/4-D sonography., Conclusion: Optimal visualization of this lesion using 3-D/4-D sonogram is helpful in providing better distinction of this lesion from other fetal facial lesions and can provide reassurance to anxious parents.

Shp2/Ptpn11 tyrosine phosphatase is a general regulator of the RTK pathways. By genetic ablation, we demonstrate that Shp2 is required for lacrimal gland budding, lens cell proliferation, survival and differentiation. Shp2 deletion disrupted ERK signaling and cell cycle regulation, which could be partially compensated by activated Kras signaling, confirming that Ras signaling was the main downstream target of Shp2 in lens and lacrimal gland development. We also showed that Sprouty2, a general suppressor of Ras signaling, was regulated by Shp2 positively at the transcriptional level and negatively at the post-translational level. Only in the absence of Sprouty2 could activated Kras signaling robustly rescue the lens proliferation and lacrimal-gland-budding defects in the Shp2 mutants. We propose that the dynamic regulation of Sprouty by Shp2 might be important not only for modulating Ras signaling in lens and lacrimal gland development, but also for RTK signaling in general.

The eye is protected by the ocular immunosurveillance system. We show that tear duct-associated lymphoid tissue (TALT) is located in the mouse lacrimal sac and shares immunological characteristics with mucosa-associated lymphoid tissues (MALTs), including the presence of M cells and immunocompetent cells for antigen uptake and subsequent generation of mucosal immune responses against ocularly encountered antigens and bacteria such as Pseudomonas aeruginosa. Initiation of TALT genesis began postnatally; it occurred even in germ-free conditions and was independent of signaling through organogenesis regulators, including inhibitor of DNA binding/differentiation 2, retinoic acid-related orphan receptor gammat, lymphotoxin (LT) alpha1beta2-LTbetaR, and lymphoid chemokines (CCL19, CCL21, and CXCL13). Thus, TALT shares immunological features with MALT but has a distinct tissue genesis mechanism and plays a key role in ocular immunity.

Eye development is a complex process that involves the formation of the retina and the lens, collectively called the eyeball, as well as the formation of auxiliary eye structures such as the eyelid, lacrimal gland, cornea and conjunctiva. The developmental requirements for the formation of each individual structure are only partially understood. We have shown previously that the homeobox-containing gene Rx is a key component in eye formation, as retinal structures do not develop and retina-specific gene expression is not observed in Rx-deficient mice. In addition, Rx-/- embryos do not develop any lens structure, despite the fact that Rx is not expressed in the lens. This demonstrates that during normal mammalian development, retina-specific gene expression is necessary for lens formation. In this paper we show that lens formation can be restored in Rx-deficient embryos experimentally, by the elimination of beta-catenin expression in the head surface ectoderm. This suggests that beta-catenin is involved in lens specification either through Wnt signaling or through its function in cell adhesion. In contrast to lens formation, we demonstrate that the development of auxiliary eye structures does not depend on retina-specific gene expression or retinal morphogenesis. These results point to the existence of two separate developmental processes involved in the formation of the eye and its associated structures. One involved in the formation of the eyeball and the second involved in the formation of the auxiliary eye structures.

The morphological and histological examinations of the lacrimal gland were conducted on pig fetuses coming from the 20th, 24th, 27th, 30th, 35th, 50th, 63rd, 94th and 112th day of gestation. The morphological examinations were carried out using the method of macroscopic preparation with a forehead magnifying glass and binocular (magnification 1.5-5.0x). In order to better visualize the anatomical elements, 60-80% absolute alcohol and 0.5-4% acetic acid solution were used for the examinations. On the 20th, 24th, 27th, and 30th day of gestation the whole fetuses were collected for the histological examinations. The whole eyeball with developing accessory organs was collected from the pig fetuses on the 35th day of gestation. On the 50th, 63rd, 94th and 112th day of gestation only the lacrimal gland was collected. Staining with H-E and Azan method was performed. On the 20th, 24th, 27th, 30th and 35th day of gestation ectodermal cells were not found in the collected material. On the 50th and 63rd day of gestation the connective tissue divides the gland parenchyma into indistinct lobes composed of gland cells. On the 94th day of gestation the number of lobes is substantially higher than on the 50th and 63rd day of gestation, while the number of lobules forming lobes decreases. On the 112th day of gestation each lobe is composed of 8-22 excretory ducts made up of the simple cuboid epithelium with a round nucleus arranged less or more peripherally.

Preferential outgrowth of the bud cells forms the basis of branching morphogenesis. Here, we show that lacrimal gland development requires specific modification of heparan sulfates by Ndst genes at the tip of the lacrimal gland bud. Systemic and conditional knockout experiments demonstrate the tissue specific requirement of Ndst1 and Ndst2 in the lacrimal gland epithelial, but not mesenchymal, cells, and the functional importance of Ndst1 in Fgf10-Fgfr2b, but not of Fgf1-Fgfr2b, complex formation. Consistent with this, Fgf10-induced ectopic lacrimal gland budding in explant cultures is dependent upon Ndst gene dose, and epithelial deletion of Fgfr2 abolishes lacrimal gland budding, its specific modification of heparan sulfate and its phosphorylation of Shp2 (Ptpn11 - Mouse Genome Informatics). Finally, we show that genetic ablation of Ndst1, Fgfr2 or Shp2 disrupts ERK signaling in lacrimal gland budding. Given the evolutionarily conserved roles of these genes, the localized activation of the Ndst-Fgfr-Shp2 genetic cascade is probably a general regulatory mechanism of FGF signaling in branching morphogenesis.

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).

The lacrimal gland produces secretions that lubricate and protect the cornea of the eye. Foxc1 encodes a forkhead/winged helix transcription factor required for the development of many embryonic organs. Autosomal dominant mutations in human FOXC1 cause eye disorders such as Axenfeld-Rieger Syndrome and glaucoma iris hypoplasia, resulting from malformation of the anterior segment of the eye. We show here that lacrimal gland development is severely impaired in homozygous null Foxc1 mouse mutants, with reduced outgrowth and branching. Foxc1 is expressed in both the epithelium of the lacrimal gland and the surrounding mesenchyme. FGF10 stimulates the growth and branching morphogenesis in cultures of wild type and Foxc1 mutant gland epithelial buds. However, using micromass culture of lacrimal gland mesenchyme, we show that Bmp7 induces wild type mesenchyme cells to aggregate, but Foxc1 mutant cells do not respond. This study demonstrates that Foxc1 mediates the BMP signaling required for lacrimal gland development., ((c) 2006 Wiley-Liss, Inc.)

The espins are a family of multifunctional actin cytoskeletal proteins. They are present in hair cell stereocilia and are the target of mutations that cause deafness and vestibular dysfunction. Here, we demonstrate that the different espin isoforms are expressed in complex spatiotemporal patterns during inner ear development. Espin 3 isoforms were prevalent in the epithelium of the otic pit, otocyst and membranous labyrinth as they underwent morphogenesis. This espin was down-regulated ahead of hair cell differentiation and during neuroblast delamination. Espin also accumulated in the epithelium of branchial clefts and pharyngeal pouches and during branching morphogenesis in other embryonic epithelial tissues, suggesting general roles for espins in epithelial morphogenesis. Espin reappeared later in inner ear development in differentiating hair cells. Its levels and compartmentalization to stereocilia increased during the formation and maturation of stereociliary bundles. Late in embryonic development, espin was also present in a tail-like process that emanated from the hair cell base. Increases in the levels of espin 1 and espin 4 isoforms correlated with stereocilium elongation and maturation in the vestibular system and cochlea, respectively. Our results suggest that the different espin isoforms play specific roles in actin cytoskeletal regulation during epithelial morphogenesis and hair cell differentiation.

The three-dimensional organization of the tear film, which is produced and drained by the different structures of the ocular adnexa, is essential for maintainance and protection of the ocular surface. This is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins, the mucins, which are usually expressed in association with a class of peptides having a well-defined, structurally conserved trefoil domain, the mammalian trefoil factor family (TFF) peptides. In this review, the latest information regarding mucin and TFF peptide function and regulation in the human lacrimal system, the tear film and the ocular surface is summarized with regard to mucous epithelia integrity, rheological and antimicrobial properties of the tear film and tear outflow, age-related changes and certain disease states such as dry eye, dacryostenosis and dacryolith formation.

The Harderian gland is a poorly understood anterior ocular gland that occurs in most terrestrial vertebrates. Numerous extraorbital functions have been ascribed to the Harderian gland, principally based on its association with the nasolacrimal duct. Few studies have centered on archosaurs and the majority of those available focused solely on the Harderian gland of birds. Little is known about the lacrimal apparatus of the crocodilians. We examined the lacrimal apparatus of several specimens of Alligator mississippiensis anatomically, histologically, and histochemically and studied the embryogenesis of this system. The nasolacrimal duct possesses a distal secretory area, which is more convoluted than that of typical mammals or lepidosaurs. The alligator Harderian gland possesses a unique combination of characteristics found in lepidosaurs, birds, and mammals. Like that of both mammals and lepidosaurs, it is a large, tuboloacinar gland that appears to secrete both mucoprotein and lipids. However, the presence of blood vessels and immune cells is reminiscent of that of the avian Harderian gland. The immunogenesis of the alligator Harderian gland appears to be tied to the development of the vascular system. The presence of a distinct palpebral gland in the anterior aspect of the ventral eyelid is a feature unique to alligators. Based on position, this gland does not appear to be homologous to the anterior lacrimal gland of lepidosaurs. Lymphatic aggregations were also found in the palpebral gland. The presence of interstitial immune cells in the orbital glands of alligators suggests that the alligator lacrimal apparatus, like that of birds, may play a role in the head-associated lymphatic tissue system., (Copyright 2005 Wiley-Liss, Inc.)

Key gene families such as FGFs and BMPs are important mediators of branching morphogenesis. To understand whether Wnt genes, and in particular, the canonical Wnt signaling pathway also function in the branching process, we have used a combination of experimental and genetic gain and loss of function approaches to perturb the levels of canonical Wnt signaling in two arborized structures, the lung and the lacrimal gland. Here, we show that the addition of Wnt3a conditioned medium or LiCl strongly represses growth and proliferation of the lung and lacrimal gland, a result that was confirmed in vivo using a dominant stable mutation of beta-catenin conditionally expressed in the lacrimal gland epithelium. In agreement with these data, knockdown of Wnt signaling with beta-catenin morpholinos results in a greater number of branches and increased cell proliferation. In addition, we show that canonical Wnt signaling is able to modulate the levels of Fgf10 and suppress BMP-induced proliferation in the lacrimal gland. Thus, canonical Wnt signaling negatively regulates branching morphogenesis providing a balance to FGFs and BMPs which positively regulate this process. This multilayered control of growth and proliferation ensures that branched structures attain the morphology required to function efficiently.

Accessory medial muscular bellies of the levator palpebrae superioris muscle and broad lateral insertion of its aponeurosis into tissue near the lacrimal gland have been reported as rare variations in adults. The anatomy of this muscle was studied in orbits of ten human fetuses between the 5th and 10th months of gestation. In each of the dissected orbits, the levator palpebrae superioris muscle had a broad lateral insertion into the capsule of the lacrimal gland or the periorbita, in this period of development. In addition, medial accessory muscles of the levator or singular muscle fibers within fibrous bands that inserted near the trochlear region and the medial portion of the upper eyelid were present in 70% of the fetuses, either unilaterally or bilaterally. These findings demonstrate new unreported aspects of levator palpebrae superioris development and morphology. Our findings suggest that an initial broad anterior primary anlage of the muscle is followed by secondary atrophy of lesser used marginal portions of this muscle, which are replaced by delicate connective tissue. These findings might force new considerations about diagnostic and therapeutic approaches to congenital mobility disorders of the levator palpebrae superioris muscle, such as blepharoptosis or eyelid retraction. The clinical relevance of our results are discussed along with a review of the embryogenesis of extraocular muscles and soft tissue of the orbit., (Copyright (c) 2005 Wiley-Liss, Inc.)

The lacrimal gland provides an excellent model with which to study the epithelial-mesenchymal interactions that are crucial to the process of branching morphogenesis. In the current study, we show that bone morphogenetic protein 7 (Bmp7) is expressed with a complex pattern in the developing gland and has an important role in regulating branching. In loss-of-function analyses, we find that Bmp7-null mice have distinctive reductions in lacrimal gland branch number, and that inhibition of Bmp activity in gland explant cultures has a very similar consequence. Consistent with this, exposure of whole-gland explants to recombinant Bmp7 results in increased branch number. In determining which cells of the gland respond directly to Bmp7, we have tested isolated mesenchyme and epithelium. We find that, as expected, Bmp4 can suppress bud extension in isolated epithelium stimulated by Fgf10, but interestingly, Bmp7 has no discernible effect. Bmp7 does, however, stimulate a distinct response in mesenchymal cells. This manifests as a promotion of cell division and formation of aggregates, and upregulation of cadherin adhesion molecules, the junctional protein connexin 43 and of alpha-smooth muscle actin. These data suggest that in this branching system, mesenchyme is the primary target of Bmp7 and that formation of mesenchymal condensations characteristic of signaling centers may be enhanced by Bmp7. Based on the activity of Bmp7 in promoting branching, we also propose a model suggesting that a discrete region of Bmp7-expressing head mesenchyme may be crucial in determining the location of the exorbital lobe of the gland.

Objectives: Fetal face malformations represent one of the most challenging prenatal diagnoses mainly because of the wide range of morphological features involved. We tested an approach based on a combination of conventional two-dimensional ultrasound with the more recent three-dimensional technique plus magnetic resonance imaging, in order to improve parents' understanding of fetal face anomalies, thereby facilitating parent counselling., Methods: Two cases of fetal facial anomaly were studied using these combined techniques; one had severe micrognathia and malformation of the ears with preauricular tags, while the other had bilateral dacryocystocele and severe hypertelorism., Results: The images generated by three-dimensional ultrasound enabled the parents to visualize their child immediately and helped them to adjust to the diagnosis of facial defects and its clinical consequences., Conclusions: An approach based on combined use of different imaging techniques was found useful in both cases., (Copyright 2004 John Wiley and Sons, Ltd.)

In this study development of the semilunar plica was examined histologycally by making sections through the eyes of eleven foetuses at different stages of gestation, two newborns and an old man. We found that in the early stages of its development the semilunar fold covered a bigger part of the orbit and later did not keep up with the growth of the eyeball and the lids. In its development three different kinds of germinal glands could be seen in the semilunar plica. Beside poorly differentiated buds of the surface epithelium which can be classified as rudiments of the nictitating or Harderian gland, serous glands were detected which could be beginnings of Krause's glands. Additionally, a new kind of plica gland was identified in which ductular structures, with an onion skin appearance, could be discriminated from mucous acini. The surface of the plica developed slowly by an increase in the layers of its epithelium as well as by the maturation of the epithelial cells from a two-layered cuboidal to a multi-layered cylindrical epithelium. In general the palpebral side of the plica consisted of a higher number of epithelial layers and more goblet cells than its bulbar side. Moreover, the surface of the palpebral side appeared more irregular and enlarged by numerous pleatings of its epithelium. The initially loose mesenchymal connective tissue was soon condensed by firstly an increase of the number of cells and later by an increase in the fibre density. In the tight collagenous connective tissue no elastic or reticular fibres or cartilaginous structures could be found. Very dense vascularization of the plica semilunaris was seen early in development. The blood vessels rising from the root of the plica divided themselves into a central and a subepithelial vascular net. Later on, some of them showed an enlarged lumen and were covered by a thin layer of muscle cells. A few unmyelinated neurofibres were found next to blood vessels and glands. Muscle cells could not be detected. A very dense concentration of leukocytes in the plica even in early intrauterine development was very striking and could be observed in this kind for the first time. These were mostly lymphoplasmocytic elements but granulocytes and macrophages could also be seen around the blood vessels and in the subepithelial area where they were arranged as follicles. Some of these cells even passed through the epithelium and could be found in the conjunctival fissure. The discovery of dense infiltration with both specific and non-specific immune cells, abundant vascularization and secretory structures (goblet cells and surface enlargement) in the semilunar plica suggest that it plays an important role as a specialized organ in human eye protection. Its anatomical position at the medial border of the eye supports this theory. Its origin from the third eyelid of the mammals could be recognized to a certain extent.

Proboscis Lateralis (PL) is one of the congenital anomalies of the nose which presents as obvious deformity. This is a report of two cases of the rare anomaly PL. One presented with right PL and the second presented with left PL. In this rare anomaly, the nasal cavity on one side is completely normal while on the affected side, the nasal cavity is replaced by a tube of skin and soft tissue attached to the inner canthus of the eye. This anomaly occurs sporadic as an isolated defect or in association with other anomalies. It is usually associated with failure of the paranasal sinuses and the nasolacrimal duct development. Embryologically, this anomaly is a result of imperfect fusion of the lateral nasal wall and maxillary processes (Int. J. Pediatr. Otorhinolaryngol. 23 (1992) 275).

The aim of this study was to determine the main stages of the lacrimal gland's developmental process in humans and to establish its precise morphogenetic timetable. Its onset is generally assumed to take place at O'Rahilly's stage 21, arising from an epithelial thickening of the superior extreme of the temporary conjunctival fornix. However, the present study points to a prior stage in the process: the presence of epithelial-mesenchymal changes in embryos at O'Rahilly's stage 19. The study was performed using light microscopy on serial sections of 37 human specimens: 23 embryos and 14 fetuses ranging from 15 to 137 mm crown-rump length (7-116 weeks of development). Three stages in lacrimal gland morphogenesis were identified: (1) the presumptive glandular stage, O'Rahilly's stages 19-20, characterized by a thickening of the superior fornix epithelium together with surrounding mesenchymal condensation; (2) the bud stage, generally assumed to be the first manifestation of glandular origin, characterized initially by the appearance of nodular formations in the region of the superior conjunctival fornix and concluding with the appearance of lumina within the epithelial buds; and (3) the glandular maturity stage, weeks 9-16, the period in which the gland begins to take on the morphology of adulthood.

Six genes are widely expressed during vertebrate embryogenesis, suggesting that they are implicated in diverse differentiation processes. To determine the functions of the Six1 gene, we constructed Six1-deficient mice by replacing its first exon by the beta-galactosidase gene. We have previously shown that mice lacking Six1 die at birth due to thoracic skeletal defects and severe muscle hypoplasia affecting most of the body muscles. Here, we report that Six1(-/-) neonates also lack a kidney and thymus, as well as displaying a strong disorganisation of craniofacial structures, namely the inner ear, the nasal cavity, the craniofacial skeleton, and the lacrimal and parotid glands. These organ defects can be correlated with Six1 expression in the embryonic primordium structures as revealed by X-Gal staining at different stages of embryogenesis. Thus, the fetal abnormalities of Six1(-/-) mice appear to result from the absence of the Six 1 homeoprotein during early stages of organogenesis. Interestingly, these Six1 defects are very similar to phenotypes caused by mutations of Eya 1, which are responsible for the BOR syndrome in humans. Close comparison of Six1 and Eya 1 deficient mice strongly suggests a functional link between these two factors. Pax gene mutations also lead to comparable phenotypes, suggesting that a regulatory network including the Pax, Six and Eya genes is required for several types of organogenesis in mammals.

It is generally difficult to find any relationship between the morphogenesis of an organ and its final function. A priori, such a relationship has no reason to exist, since organs do not actually function during their formation. I will show in this article that, for a very large class of organs--the branched organs--there exists a hidden relationship between their morphogenesis and their function. This class of organs comprises: the lungs, the salivary mammary and lacrymal glands, the kidneys, the pancreas, and possibly other organs, such as testes. For all these organs, a fundamental fact that comes from recent developments in physics explains at the same time how they form, and why they work. This suggests, first, that complex organs are not the result of gradual and long selection processes, and, second, that this specific structure for the organs is imposed by the laws of physics. The growth process, as described here, is possibly the only one that allows both to build a fluid-secreting organ, and make it work.

Objective: Hypohidrotic ectodermal dysplasia (HED) comprises defects in hair, teeth, and sweat glands. Disturbances in other ectodermal tissues have been associated with the condition. Our objective was to examine ectodermal craniofacial structures histologically in a fetus with HED and to compare the findings to similar structures in normal control fetuses., Materials and Methods: A male fetus diagnosed with HED was therapeutically aborted in the 15th week of gestation. One male and two female healthy fetuses were used as normal controls. All fetuses were examined with parental consent, and had comparable sizes. Their bone maturation stage in the hand was identical. Tissue blocks from the craniofacial region were excised from all fetuses and prepared for histological analysis (formalin fixed, stained with toluidine blue or Alcian blue). The tissues examined were: tooth buds, skin and skin appendages, oral mucosa including minor salivary glands, major salivary glands, lacrimal glands, and adenohypophysis., Results: Fewer tooth buds, minor salivary glands, and hair follicles were observed in the HED fetus as compared to controls. The structures of the epidermal components in the developing HED organs were loose and disorganised. The adhesion between the ectodermal and mesenchymal organ components in the HED fetus seemed to be disturbed.

A variety of congenital midface anomalies occur in children. High-resolution computed tomography (CT) and magnetic resonance (MR) imaging have proved helpful in determining the nature and extent of dysplasia, thereby facilitating treatment planning. A classification system has been developed that groups these anomalies into four categories based on embryogenesis and anatomic location. These categories comprise anomalies that are related to the nasal cavity, nasofrontal region, nasolacrimal apparatus, and craniofacial syndromes. CT is the imaging modality of choice in children with possible choanal atresia, pyriform aperture stenosis, or anomalies of the nasolacrimal duct (eg, nasolacrimal duct stenosis, dacryocystoceles). MR imaging is the modality of choice in patients with congenital midface masses (eg, dermoid and epidermoid cysts, nasal gliomas, encephaloceles) and craniofacial syndromes (eg, Apert syndrome, Crouzon syndrome, Treacher Collins syndrome). In many cases, however, both CT and MR imaging are required to adequately evaluate midface anomalies. Familiarity with the characteristic imaging features of these anomalies along with knowledge of midface embryogenesis and normal developmental anatomy is essential to prevent misinterpretation of anatomic variations that may simulate disease.

We investigated the mechanism of tissue induction and specification using the lacrimal gland as a model system. This structure begins its morphogenesis as a bud-like outgrowth of the conjunctival epithelium and ultimately forms a branched structure with secretory function. Using a reporter transgene as a specific marker for gland epithelium, we show that the transcription factor Pax6 is required for normal development of the gland and is probably an important competence factor. In investigating the cell-cell signaling required, we show that fibroblast growth factor (FGF) 10 is sufficient to stimulate ectopic lacrimal bud formation in ocular explants. Expression of FGF10 in the mesenchyme adjacent to the presumptive lacrimal bud and absence of lacrimal gland development in FGF10-null mice strongly suggest that it is an endogenous inducer. This was supported by the observation that inhibition of signaling by a receptor for FGF10 (receptor 2 IIIb) suppressed development of the endogenous lacrimal bud. In explants of mesenchyme-free gland epithelium, FGF10 stimulated growth but not branching morphogenesis. This suggested that its role in induction is to stimulate proliferation and, in turn, that FGF10 combines with other factors to provide the instructive signals required for lacrimal gland development.

The orbital glands of the lizard Podarcis s. sicula are represented by the anterior and posterior lacrimal glands and the Harderian gland. The anlage of the Harderian gland appears on about the 22nd day of development in the form of a short tubule projecting from the conjunctival epithelium. This event is coincident with the appearance of the nictitating membrane. At this stage the mesenchymal cells surrounding the glandular blastema proliferate at a high rate and form a definite sac, later occupied by both the Harderian gland and the anterior lacrimal glands. At the 26th day of development, the glandular blastema forms acini at its distal end. The prospective glandular cells are not yet differentiated histologically. At the 36th day of development, differentiated serous glandular cells become visible. At the 41st day of development, the acini fill up the preformed mesenchymal sac. Only at this stage does the most medial part of the gland differentiate into mucous-secreting anterior lacrimal gland. At the same time, a small primordium of the posterior lacrimal gland can be seen in the posterior commissure of the eye. The appearance of junctional complexes between epithelial cells and mesenchymal cells in the early developmental stages supports the role of the mesenchyme in the differentiation of the glandular cells. Since the glandular anlage differentiates laterally into Harderian gland and medially into anterior lacrimal gland, spatial and temporal differences seem to exist in the inductive process. Furthermore, a concentration gradient of the inductive substance(s) may be envisaged, since an intermediate zone is present between the Harderian gland and the anterior lacrimal gland, consisting of mixed glandular cells containing both mucous and serous secretory granules.

The embryonal and fetal development of the human eye includes a series of sequential events starting with the fertilization of the ovum and culminating in the birth of a normal baby. Three main periods can be distinguished in the prenatal development of the eye. The first period called embryogenesis is characterized by the establishment of the primary organ rudiments and ends at the end of the 3rd week with the appearance of the optic sulci on both sides of the midline at the expanded cranial end of the still open neural folds. The second period called organogenesis includes the development of the primary organ rudiments and extends till the end of the 8th week. The third period involves the differentiation of each of the primitive organs into a fully or partially active organ and is called differentiation. The period of embryogenesis is characterized by the appearance and migration of the neural crest cells and by the formation of the primary brain vesicles. The period of organogenesis extends from the 4th week till the end of the 8th week. The 4th week shows the closure of the neural canal anteriorly with the subsequent evagination of its lateral wall into optic vesicles, the invagination of the lower nasal wall of the optic vesicle causing the formation of the optic cup, and the development of the lens plate, retinal disk and embryonic fissure. The embryonic fissure extends into the optic stalk which connects the cavity of the optic vesicle with the cavity of the neural canal; the hyaloid artery penetrates into the optic cup through the embryonic fissure. During the 5th week, the optic cup is concluded, and the cells of its external layer acquire pigmentation as a result of contact with developing capillaries in the periocular mesenchyme; these capillaries anastomose with each other and form anteriorly the annular vessel. The lens plate develops into a lens pit and later into a lens vesicle which separates soon thereafter from the surface ectoderm. Inside the optic cup, the hyaloid vessels form the capillaries of the posterior tunica vasculosa lentis and through the capillaries of the lateral tunica vasculosa lentis anastomose with the annular vessel. The primary vitreous forms and the surface ectoderm overlying the lens vesicle differentiates into a primitive corneal epithelium. The facial and orbital structures also develop at this stage. The 6th week shows the incipient differentiation of the inner layer of the optic cup into a sensory retina, the formation of the secondary vitreous, the transformation of the posterior cells of the lens vesicle into primary lens fibers, the development of the periocular vasculature and the appearance of the first eyelid folds and of the anlage of the nasolacrimal duct. However, the dominating factor is the closure of the embryonic fissure.(ABSTRACT TRUNCATED AT 400 WORDS)

In 50 human embryos at the age of 21 days--12 weeks of development, including the stages X-XXIII and beginning of the fetal period according to Carnegie's classification, spatial-temporal regularities on rearrangement of cellular material in the mesenchymal derivatives of the ocular auxiliary apparatus have been investigated. The main attention has been paid to ascertain the moments, when the first signs of differences appear in the previously homogenous cellular material of the differentiating mesenchyme around the ocular cup and in the eyelids, taking into account appearance of derivates in the ocular auxiliary apparatus: sclera, oculomotor muscles, stroma of the lacrimal gland, cartilagenous laminae in the eyelids and in the orbicular muscle. Regularities of cytochemical differentiation of the mesenchyme and its derivatives have been studied, taking into account the organ's changing topography. Morphometrical investigations of cells in the anlages mentioned are expanded and correlated with the time of their cytochemical differentiation. Correlation of the morphometrical and cytochemical data with the histological investigations has been performed.

Immunohistochemical staining with antineuronal-specific enolase antibodies showed a positive reaction product in the acini and in the nerves of human major and accessory lacrimal glands. The fibrous tissue interstitium, septae, capsule, and blood vessels reacted negatively. Our findings indicate that the acinar portion of the lacrimal gland, but not the fibrous tissue component, is derived from neuroectoderm. We propose that the acini of the human lacrimal glands develop, not as an ingrowth into the mesenchymal stroma from the surface ectoderm that forms the conjunctiva, but as an outgrowth from the embryonic neuroectoderm, and more specifically, from cells that have migrated from the neural crest.

The relations between the saccus lacrimalis and different portions of the musculus orbicularis oculi were studied in orbital regions of human fetuses sectioned into numbered series. No insertions of the pars lacrimalis or Horner's muscle on the saccus were found. These muscular fibres pass along the dorsal wall of the saccus and are separated from it by the reflex tendon of the ligamentum palpebrale mediale. The only muscular fibres that insert on the saccus are those that approach the anterior face of the saccus and the fornix. The fibres that insert on the anterior face proceed from the deep bundles of the pars preseptalis of the lower eyelids, and those that insert on the fornix derive from the deep bundles of the pars preseptalis of the upper eyelid.

The development of the nasolacrimal apparatus was reassessed based on the examination of serial sections done in 27 (54 orbits) embryos and fetuses ranging in size from 13.6 mm to term. In addition two adult specimens were examined. The entire nasolacrimal apparatus viz. canaliculi, lacrimal sac, and nasolacrimal duct develop contemporaneously. Canalization thereafter occurs throughout its length at the same time. The epithelium which lines the nasolacrimal apparatus abuts against the conjunctival epithelium superiorly in relationship to the puncta and the nasal mucosa at the opening of the nasolacrimal duct. These gossamer-like membranes perforate at term or soon thereafter. With the development of the face, the maxillary process grows medially to abut against, and then to override, the paraxial mesoderm of the nasolacrimal process. The nasooptic fissure is thus formed between these two mesodermal complexes. The surface ectoderm within the fissure thickens in a cord-like fashion and this is the analaga of the nasolacrimal apparatus. There is divergence of opinion as to the subsequent development of tear drainage system. A cord of epithelial cells forms from the nasal cavity and grows cephalad to become continuous with the main cord of buried surface ectoderm (Figure 1). It has been contended by Duke-Elder that the main epithelial cord then sends extensions laterally to form the superior and the inferior canaliculi. The inferior canaliculus extends more laterally than the superior canaliculus. At 3 months' development, canalization of the nasolacrimal apparatus is purported to occur in a segmental manner. These cavities then coalesce in a haphazard manner, finally forming a continuous tube. It is also suggested that the main core of buried epithelium canalizes from cephal caudalwards and that the epithelium arising from the nasal cavity canalizes in a reverse direction. The lacrimal sac then expands: the canaliculi canalize and the final section of the nasolacrimal duct to become patent is the opening into the inferior meatus of the nose below the inferior meatus of the nose below the inferior turbinate.U

The Harderian gland of the chcken develops from epithelial cones of the conjunctiva between the 11th and 12th day of embryonal life. The development of the organ proceeds in two phases. During the stage of epithelial development (days 13 to 17 of embryonal life) the acinar epithelium differentiates into a lumen-adjacent glandular epithelium, and a separate layer of basal epithelial cells. This basal layer is initially compact but later forms a loose meshwork. The basal cells differ from the myoepithelial cells found in the Harderian gland of rodents by virtue of their smaller number of myofilaments; and they resemble the reticuloepithelial cells in the Bursa of Fabricius. On days 17 and 18 of embryonal life the interstitial tissue is invaded by eosinophils and by small 'blasts', up to 4 microns in diameter, both of vascular origin. Between days 17 and 20 the glandular epithelium undergoes secretory transformation. At the time of hatching (day 21), the secretory function is fully developed. The mode of secretion is partly apocrine, partly merocrine. During the following phase of plasmacellular development (from day 17 of prenatal until day thirty of postnatal life) interstitial plasma cells are formed from the immigrant small 'blasts'. Their number increases until the fourth week after hatching; thereafter the plasma cell population remains stable.

Discussed is the treatment of a variety of conditions that affect the structures responsible for the production and drainage of tears.