Recent studies have established that the phenotype of epithelial stem cells residing in the corneal periphery (the limbus) depends on this niche’s distinct biomechanical properties. However, the signaling pathways underlying this dependency are still poorly understood. To address this issue, we investigated the effect of substrate stiffness on the migration, proliferation, and molecular phenotype of human limbal epithelial stem cells (LESCs). Specifically, we demonstrated that cells grown on collagen-based substrates with limbus-like compliance showed higher proliferation and stratification and lower migration capabilities, as well as higher levels of pro-proliferative markers Ki67 and β-Catenin, and LESC markers ΔNp63, ABCG2, and CK15. In contrast, cells on stiffer substrates lost these stem/progenitor cell markers, but instead expressed the key mechanotransduction factor YAP, as well as elevated levels of BMP4, a promotor of cell differentiation known to be negatively regulated by Wnt/β-Catenin signaling. This data allowed us to propose a new model that integrates the various molecular pathways involved in LESC response to substrate stiffness. This model will potentially be a useful guide to future research on the mechanisms underlying LESC loss following fibrosis-causing injuries.

Ring1 and Yy1 Binding Protein (Rybp) has been implicated in transcriptional regulation, apoptotic signaling and as a member of the polycomb repressive complex 1 has important function in regulating pluripotency and differentiation of embryonic stem cells. Earlier, we have proven that Rybp plays essential role in mouse embryonic and central nervous system development. This work identifies Rybp, as a critical regulator of heart development. Rybp is readily detectable in the developing mouse heart from day 8.5 of embryonic development.Prominent Rybp expression persists during all embryonic stages and Rybp marks differentiated cell types of the heart. By utilizing rybp null embryonic stem cells (ESCs) in an in vitro cardiac differentiation assay we found that rybp null ESCs do not form rhythmically beating cardiomyocytes. Gene expression profiles revealed a down-regulation of terminal cardiac and upregulation of germ line specific markers in the rybp null cardiomyocytes. Furthermore, transcriptome analysis uncovered a number of novel candidate target genes regulated by Rybp.Among these are several important in cardiac development and contractility such as Plagl1, Isl1, This article has been peer-reviewed and accepted for publication, but has yet to undergo copyediting and proof correction. The final published version may differ from this proof. 2Tnnt2. Importantly, forced expression of rybp in rybp deficient ESCs by a lentiviral vector was able to rescue the mutant phenotype. Our data provides evidence for a previously unrecognized function of Rybp in heart development.and pointing out the importance of germ cell lineage gene silencing during somatic differentiation. IntroductionA complex network of transcription factors governs the temporal and spatial patterns of gene expression in the organs of the developing embryo proper. Transcription factors also have important roles in postnatal and adult life in maintaining the pattern of differentiated gene expression [1][2][3]. Ring1 and Yy1 binding protein (Rybp; or also known as Dedaf (Death Effector Domain Associated Factor), UniGene Mm.321633; MGI:1929059) is a repressor protein that is also a member of the mammalian polycomb repressive complex 1 (PRC1) [4]. Rybp first was described as binding partner for the polycomb group protein (PcG) Ring1A (Ring1; ortholog of Drosophila dRing/Sce) and also was shown to associate with Ring1B (Ring2/Rnf2; ortholog of Drosophila dRing/Sce) and M33 (Pc1; ortholog of Drosophila Pc), components of the PRC1 multiprotein complex [5]. Our previous work showed that Rybp is selectively upregulated in distinct structures and cell types of the developing eye and the central nervous system (CNS) and, may also play a role in the development of more mature neurons [6,7]. We have also shown that rybp is essential for the development of the mouse embryo proper and that homozygous null mouse embryos cannot develop further implantation (embryonic day 5.5 (E5.5)). Notably, in a subset of heterozygous animals and in rybp −/− ↔rybp +/+ chimeras, alt...