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    • In keep with our observation that chemokines

    2018-10-22

    In keep with our observation that chemokines are highly expressed by limbal progenitors, others have identified CXCL12 as the most highly expressed gene by LESC compared to central cornea epithelial gtpase inhibitor by microarray (Nieto-Miguel et al., 2011). In a similar study, Takacs and colleagues identified CXCL2/MIP-2 and CXCR4 as highly up-regulated in their human genome expression array (Takacs et al., 2011). Curiously, they also noted high expression of interferon-induced transmembrane protein-1 (IFITM1) and IFITM2 in their arrays. Likewise, Akinci and co-authors discovered CXCR4 as the most highly up-regulated gene in porcine limbal side population cells compared to non-side population cells (Akinci et al., 2009). Bian et al. (2010b) characterized the molecular signature and biological pathways of limbal epithelial cell that were rapidly adherent to collagen type IV (regarded as having progenitor-like qualities Li et al., 2005), in which they identified Chromosome 10 open reading frame 10 (C10orf10) as the second highest gene expressed in adherent, compared to non-adherent cells. Our analysis unveiled a related member (C10orf116) as the highest expressed gene (Supplementary Table 2); however the precise function of these genes is currently unknown. Bian et al. also identified down-regulation of carcinoembryonic antigen-related cell adhesion molecules (CEACAM)-1, 5, 6, and 7 (Bian et al., 2010b), a result which contrasted with the enhanced expression of CEACAM-6 in our array (Supplementary Table 2). These differences could be related to the phenotype of cells used in each study. We also identified kallikrein-related peptidase 6 (KLK6), a gene found by Albert et al. in LESC cultured on lens capsules (Albert et al., 2012). Future investigations will focus on determining the role of interferon and chemokine signaling in supporting LESC function.
    Acknowledgments
    Introduction Human adipose tissue-derived stromal cells (hASC) are readily isolated from the pools of cells resident in the vascular stroma of adipose tissue. ASCs proliferate and self-renew and, due to their multipotent nature, they can differentiate at least in vitro into several tissue-specific lineages, including the chondrogenic, osteogenic, adipogenic and miogenic lineages (De Ugarte et al., 2003; Gimble et al., 2007). Adipose tissue is ubiquitous and large quantities are easily accessible with minimal invasion procedures (Baer and Geiger, 2012). These characteristics make these cells ideal candidates for use in cell therapy. An understanding of the biological process committing the cell to differentiation into a specific cell type is essential for the successful repair of injured tissue. Cytokines, growth factors and extracellular matrix components in the microenvironment determine stem cell fate, by regulating the switch from self-renewal to differentiation (Kratchmarova et al., 2005). However, the downstream effectors and the gene regulatory networks controlling these processes remain unclear. Gene expression profiling has provided insight into the molecular pathways involved in ASC self-renewal and differentiation (Ivanova et al., 2002; Song et al., 2006). Genome-wide analyses based on microarray hybridization and, more recently, next generation sequencing, have been carried out to assess the global expression of gene networks. Most attempts to determine the mRNA profile of self-renewing or differentiating cells have made use of total RNA for hybridization to microarrays or RNA-Seq analysis (Jeong et al., 2007a; Menssen et al., 2011). High-throughput analyses in eukaryotes comparing mRNA and protein levels have indicated that there is no direct correlation between transcript levels and protein synthesis, suggesting a high degree of posttranscriptional regulation in eukaryote cells (Washburn et al., 2003; Keene, 2007; Tebaldi et al., 2012). This hampers the classical transcriptome-based approach to investigate controlled expression in differentiating cells. Protein abundance can be controlled and refined through the regulation of gene expression at various complementary levels. Several lines of evidence from different organisms suggest that stem cell self-renewal and differentiation are also dependent on the control of protein synthesis by posttranscriptional mechanisms (Keene, 2007; Sampath et al., 2008; Haston et al., 2009; Kolle et al., 2011). The analysis of the mRNA fraction associated to polysomes has been used as a strategy to analyze posttranscriptional mechanisms involved in the control of translation (Fromm-Dornieden et al., 2012). This posttranscriptional regulation is mediated by various molecules, such as microRNAs, noncoding RNAs and RNA binding proteins. Trans-acting factors recognize and bind sequences or structural elements, mostly in the untranslated regions (UTRs) of mRNAs (Mittal et al., 2009; Bar et al., 2008; Keene, 2010). Posttranscriptional control may be mediated by, amongst other things, modifications to mRNA stability or by the inhibition of transcript association with translating ribosomes.