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Purpose: Animal models are pivotal for elucidating pathophysiological mechanisms and evaluating novel therapies. This systematic review identified studies that developed or adapted animal models of limbal stem cell deficiency (LSCD), assessed their reporting quality, summarized their key characteristics, and established their clinical translational relevance to human disease., Methods: The protocol was prospectively registered (PROSPERO CRD42020203937). Searches were conducted in PubMed, Ovid EMBASE and Web of Science in August 2020. Two authors screened citations, extracted data, assessed the reporting quality of eligible studies using the ARRIVE guidelines, and judged the clinical translational relevance of each model using a custom matrix., Results: 105 studies were included. Rabbits were the most common animal species. Overall, 97% of studies recapitulated LSCD to a clinical etiology, however 62% did not provide sufficient methodological detail to enable independent reproduction of the model. Adverse events and/or exclusion of animals were infrequently (20%) reported. Approximately one-quarter of studies did not produce the intended severity of LSCD; 34% provided insufficient information to assess the fidelity of disease induction. Adjunctive diagnostic confirmation of LSCD induction was performed in 13% of studies., Conclusions: This is the first systematic review to assess the reporting quality and clinical translational relevance of animal models of LSCD. Models of LSCD have evolved over time, resulting in variable reporting of the characteristics of animals, experimental procedures and adverse events. In most studies, validation of LSCD was made using clinical tests; newer adjunctive techniques would enhance diagnostic validation. As most studies sought to evaluate novel therapies for LSCD, animal models should ideally recapitulate all features of the condition that develop in patients., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

The dynamics of epithelial stem cells (SCs) that contribute to the formation and maintenance of the cornea are poorly understood. Here, we used K14CreER T2 -Confetti (Confetti) mice, sophisticated imaging, and computational modeling to trace the origins and fate of these cells during embryogenesis and adult life. We show that keratin-14 (K14 + )-expressing progenitors are defined and widely distributed across the E16.5 cornea, after which they undergo cycles of proliferation and dispersal prior to eyelid opening. K14 + clonal patches disappear from the central cornea and are replaced by limbal-derived K14 + streaks, a finding that aligned with bromodeoxyuridine label-retaining studies. We also elucidated the mechanism by which SC clones are lost during life and propose this is due to population asymmetry and neutral drift. Finally, we established that the occurrence of an equatorial migratory mid-line is a consequence of apoptosis in a narrow nasal-temporal region, the site where eyelids meet during blinking., (Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.)

The cornea sits at the anterior aspect of the eye and, like the skin, is highly exposed to ultraviolet radiation (UVR). The cornea blocks a significant proportion of UVB from reaching the posterior structures of the eye. However, UVA can penetrate the full thickness of the cornea, even reaching the anterior portion of the lens. Epidemiological data indicate that UVR is a contributing factor for a multitude of diseases of the cornea including pterygium, photokeratitis, climatic droplet keratopathy and ocular surface squamous neoplasia (OSSN), although the pathogenic mechanisms of each require further elucidation. UVR is a well-known genotoxic agent, and its effects have been well characterized in organs such as the skin. However, we are only beginning to identify its effects on the cornea, such as the UVR signature C → T and CC → TT transversions identified by sequencing and increased proliferative and shedding rates in response to UVR exposure. Alarmingly, a single low-dose exposure of UVR to the cornea is sufficient to elicit genetic, molecular and cellular changes, supporting the consideration of using protective measures, such as wearing sunglasses when outdoors. The aim of this review was to describe the adverse effects of UVR on the cornea., (© 2016 The American Society of Photobiology.)

Maintaining the structure of the cornea is essential for high-quality vision. In adult mammals, corneal epithelial cells emanate from stem cells in the limbus, driven by an unknown mechanism towards the centre of the cornea as cohesive clonal groups. Here we use complementary mathematical and biological models to show that corneal epithelial cells can self-organize into a cohesive, centripetal growth pattern in the absence of external physiological cues. Three conditions are required: a circumferential location of stem cells, a limited number of cell divisions and mobility in response to population pressure. We have used these complementary models to provide explanations for the increased rate of centripetal migration caused by wounding and the potential for stem cell leakage to account for stable transplants derived from central corneal tissue, despite the predominantly limbal location of stem cells.

Stem cell (SC) division, deployment, and differentiation are processes that contribute to corneal epithelial renewal. Until now studying the destiny of these cells in a living mammal has not been possible. However, the advent of inducible multicolor genetic tagging and powerful imaging technologies has rendered this achievable in the translucent and readily accessible murine cornea. K14CreER(T2)-Confetti mice that harbor two copies of the Brainbow 2.1 cassette, yielding up to 10 colors from the stochastic recombination of fluorescent proteins, were used to monitor K-14(+) progenitor cell dynamics within the corneal epithelium in live animals. Multicolored columns of cells emerged from the basal limbal epithelium as they expanded and migrated linearly at a rate of 10.8 µm/day toward the central cornea. Moreover, the permanent expression of fluorophores, passed on from progenitor to progeny, assisted in discriminating individual clones as spectrally distinct streaks containing more than 1,000 cells within the illuminated area. The centripetal clonal expansion is suggestive that a single progenitor cell is responsible for maintaining a narrow corridor of corneal epithelial cells. Our data are in agreement with the limbus as the repository for SC as opposed to SC being distributed throughout the central cornea. This is the first report describing stem/progenitor cell fate determination in the murine cornea using multicolor genetic tracing. This model represents a powerful new resource to monitor SC kinetics and fate choice under homeostatic conditions, and may assist in assessing clonal evolution during corneal development, aging, wound-healing, disease, and following transplantation., (© 2014 AlphaMed Press.)

The recent elucidation of the genomic landscape of head and neck squamous cell carcinoma (HNSCC) has provided a unique opportunity to develop selective cancer treatment options. These efforts will require the establishment of relevant HNSCC models for preclinical testing. Here, we performed full exome and transcriptome sequencing of a large panel of HNSCC-derived cells from different anatomical locations and human papillomavirus (HPV) infection status. These cells exhibit typical mutations in TP53, FAT1, CDK2NA, CASP8, and NOTCH1, and copy number variations (CNVs) and mutations in PIK3CA, HRAS, and PTEN that reflect the widespread activation of the PI3K-mTOR pathway. SMAD4 alterations were observed that may explain the decreased tumor suppressive effect of TGF-β in HNSCC. Surprisingly, we identified HPV+ HNSCC cells harboring TP53 mutations, and documented aberrant TP53 expression in a subset of HPV+ HNSCC cases. This analysis also revealed that most HNSCC cells harbor multiple mutations and CNVs in epigenetic modifiers (e.g., EP300, CREBP, MLL1, MLL2, MLL3, KDM6A, and KDM6B) that may contribute to HNSCC initiation and progression. These genetically-defined experimental HNSCC cellular systems, together with the identification of novel actionable molecular targets, may now facilitate the pre-clinical evaluation of emerging therapeutic agents in tumors exhibiting each precise genomic alteration.

Keratinocytes are the cells in vertebrates that form the frontline barrier to the environment, and are also the most common origin of human cancer. They normally retain tight cell-cell adhesion and low motility, allowing them to terminally differentiate as they stratify. However, they must be able to respond to tissue damage by migrating into and across wounds. This requires reduced mutual adhesion, suppressed terminal differentiation and increased motility, processes driven by the Snail family of transcriptional repressors. The quantity, location and activity of Snail proteins are regulated by growth factors and cytokines to mediate these responses and invoke an inflammatory response. Subversion of these same pathways can promote carcinoma invasion and metastasis. Signaling network facts: • Snail1 and Snail2 in keratinocytes are important in promoting migration, inflammation and carcinogenesis, and suppressing terminal differentiation. • Extracellular stimuli, including TGFR and EGFR ligands, regulate Snails transcriptionally, via SMAD and MAPK pathways, and post-translationally, by modulating GSK3 and PAK1 activity, which determine Snail stability and intracellular location. • Snails directly repress transcription of genes important for cell-cell adhesion and cornified envelope formation. • Down-regulation of epithelial cadherins by Snails allows LIMDPs to relocate from adherens junctions to the cytoplasm, where they stimulate MAPK pathways, and to the nucleus, where they bind directly to Snails and act as corepressors. • Snail2 is essential for re-epithelialization of healing wounds and can be up-regulated in the keratinocytes at wound margins by p38, ERK1/2 and ERK5 MAPKs, and the arylhydrocarbon receptor. • Further information on signaling related to Snail proteins can be found online at KEGG: http://www.genome.jp/kegg-bin/show pathway?hsa04520 http://www.genome.jp/kegg-bin/show_pathway?hsa04350 http://www.genome.jp/kegg-bin/show pathway?hsa04012., (Copyright © 2010 Elsevier Ltd. All rights reserved.)