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Comparative transcriptional profiling of the limbal epithelial crypt demonstrates its putative stem cell niche characteristics.

ABSTRACT: BACKGROUND: The Limbal epithelial crypt (LEC) is a solid cord of cells, approximately 120 microns long. It arises from the undersurface of interpalisade rete ridges of the limbal palisades of Vogt and extends deeper into the limbal stroma parallel or perpendicular to the palisade. There are up to 6 or 7 such LEC, variably distributed along the limbus in each human eye. Morphological and immunohistochemical studies on the limbal epithelial crypt (LEC) have demonstrated the presence of limbal stem cells in this region. The purpose of this microarray study was to characterise the transcriptional profile of the LEC and compare with other ocular surface epithelial regions to support our hypothesis that LEC preferentially harbours stem cells (SC). RESULTS: LEC was found to be enriched for SC related Gene Ontology (GO) terms including those identified in quiescent adult SC, however similar to cornea, limbus had significant GO terms related to proliferating SC, transient amplifying cells (TAC) and differentiated cells (DC). LEC and limbus were metabolically dormant with low protein synthesis and downregulated cell cycling. Cornea had upregulated genes for cell cycling and self renewal such as FZD7, BTG1, CCNG, and STAT3 which were identified from other SC populations. Upregulated gene expression for growth factors, cytokines, WNT, Notch, TGF-Beta pathways involved in cell proliferation and differentiation were noted in cornea. LEC had highest number of expressed sequence tags (ESTs), downregulated and unknown genes, compared to other regions. Genes expressed in LEC such as CDH1, SERPINF1, LEF1, FRZB1, KRT19, SOD2, EGR1 are known to be involved in SC maintenance. Genes of interest, in LEC belonging to the category of cell adhesion molecules, WNT and Notch signalling pathway were validated with real-time PCR and immunofluorescence. CONCLUSIONS: Our transcriptional profiling study identifies the LEC as a preferential site for limbal SC with some characteristics suggesting that it could function as a 'SC niche' supporting quiescent SC. It also strengthens the evidence for the presence of "transient cells" in the corneal epithelium. These cells are immediate progeny of SC with self-renewal capacity and could be responsible for maintaining epithelial turn over in normal healthy conditions of the ocular surface (OS). The limbus has mixed population of differentiated and undifferentiated cells.

SUBMITTER: Kulkarni BB

PROVIDER: S-EPMC2997017 | biostudies-literature | 2010

REPOSITORIES: biostudies-literature

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Comparative transcriptional profiling of the limbal epithelial crypt demonstrates its putative stem cell niche characteristics.

Kulkarni Bina B BB Tighe Patrick J PJ Mohammed Imran I Yeung Aaron M AM Powe Desmond G DG Hopkinson Andrew A Shanmuganathan Vijay A VA Dua Harminder S HS

BMC genomics 20100929

<h4>Background</h4>The Limbal epithelial crypt (LEC) is a solid cord of cells, approximately 120 microns long. It arises from the undersurface of interpalisade rete ridges of the limbal palisades of Vogt and extends deeper into the limbal stroma parallel or perpendicular to the palisade. There are up to 6 or 7 such LEC, variably distributed along the limbus in each human eye. Morphological and immunohistochemical studies on the limbal epithelial crypt (LEC) have demonstrated the presence of limb ...[more]

PMID: 20920242

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Project description:Human interfollicular epidermis is sustained by the proliferation of stem cells and their progeny, transient amplifying cells. Molecular characterization of these two cell populations is essential for better understanding of self renewal, differentiation and mechanisms of skin pathogenesis. The purpose of this study was to obtain gene expression profiles of alpha 6+/MHCI+, transient amplifying cells and alpha 6+/MHCI-, putative stem cells, and to compare them with existing data bases of gene expression profiles of hair follicle stem cells. The expression of Major Histocompatibility Complex (MHC) class I, previously shown to be absent in stem cells in several tissues, and alpha 6 integrin were used to isolate MHCI positive basal cells, and MHCI low/negative basal cells.Transcriptional profiles of the two cell populations were determined and comparisons made with published data for hair follicle stem cell gene expression profiles. We demonstrate that presumptive interfollicular stem cells, alpha 6+/MHCI- cells, are enriched in messenger RNAs encoding surface receptors, cell adhesion molecules, extracellular matrix proteins, transcripts encoding members of IFN-alpha family proteins and components of IFN signaling, but contain lower levels of transcripts encoding proteins which take part in energy metabolism, cell cycle, ribosome biosynthesis, splicing, protein translation, degradation, DNA replication, repair, and chromosome remodeling. Furthermore, our data indicate that the cell signaling pathways Notch1 and NF-kappaB are downregulated/inhibited in MHC negative basal cells.This study demonstrates that alpha 6+/MHCI- cells have additional characteristics attributed to stem cells. Moreover, the transcription profile of alpha 6+/MHCI- cells shows similarities to transcription profiles of mouse hair follicle bulge cells known to be enriched for stem cells. Collectively, our data suggests that alpha 6+/MHCI- cells may be enriched for stem cells. This study is the first comprehensive gene expression profile of putative human epithelial stem cells and their progeny that were isolated directly from neonatal foreskin tissue. Our study is important for understanding self renewal and differentiation of epidermal stem cells, and for elucidating signaling pathways involved in those processes. The generated data base may serve those working with other human epithelial tissue progenitors.

Project description:Recently we had discovered a solid cord like structure at the limbus of human eyes, termed as the Limbal Epithelial Crypt (LEC). It arises from the undersurface of the interpalisade rete ridges and extends towards the conjunctiva over the conjunctival stroma. Anatomical and immunohistochemical studies have shown it to be potentially a Stem Cell Niche. To confirm this hypothesis we conducted comparative gene expression profile of LEC with pathway and Geneontology studies in comparison with other ocular surface epithelial regions such as cornea, limbus, LEC stroma and conjunctiva. Frozen tissue blocks of corneoscleral buttons dissected from cadaver eyes were cryosectioned. These tissue sections from different ocular surface regions were laser microdissected. Extracted RNA was amplified & hybridized to 30,000k Human spotted cDNA microarray chips. Raw data obtained with Genepix Pro6 software was filtered, normalized & analysed on BASE & Jexpresspro software. Unpaired T-Test, Significance Analysis of Microarrays were performed on the data. Database for Annotation, Visualisation, and Integrated Discovery (DAVID) (http://www.DAVID.niaid.nih.gov) and Ingenuity Pathway Analysis (IPA) was used to determine the enriched GO terms and pathways in the differentially expressed genes. Quantitative gene expression analysis (qPCR) and immunohistochemistry was performed on the genes of interest. Statistical analysis for real time PCR was performed on SPSS16 to determine the normalised expression of gene of interest on ocular surface regions. Samples were prepared from five human ocular surface epithelial regions such as Cornea, Limbus, LEC, LEC Stroma, Conjunctiva. There were four replicates in each groups except Cornea and Conjunctiva with 3 each. The Standard Probe (SP) was prepared from mixing equal amount of Corneal and conjunctival epithelial RNA followed by ethanol precipitation. Samples were labelled with Cy5 dye and Standard Probe with Cy3 Dye. These were mixed in equal amount to prepare hybrid probes which were then hybridised to microarray slide.

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Comparative transcriptional profiling of the limbal epithelial crypt demonstrates its putative stem cell niche characteristics.

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Comparative transcriptional profiling of the limbal epithelial crypt demonstrates its putative stem cell niche characteristics.

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