Among numerous microscopically visible nuclear substructures, the nucleolus is the most prominent and represents a functionally and biophysically distinct body or compartment. The nucleolus is, in fact, so prominent that it drew the attention of early biologists over 200 years ago, in light microscopy studies by Fontana, Valentin and Wagner 1. Following these early descriptions came the understanding of the functional importance of the nucleolus, including its primary role as the site for the initial steps of ribosome biogenesis, including RNA polymerase I (Pol I)-driven transcription, processing and modification of ribosomal RNA (rRNA) and the assembly of rRNA-containing complexes 2 (Fig. 1). These processes involve several hundred protein transacting factors and small nucleolar RNAs 3 , which serve to guide the specificity of rRNA chemical modifications, pre-rRNA folding and cleavage. Once precursor subunits are released from the nucleolar structure, they undergo further maturation in the nucleoplasm and cytoplasm prior to becoming fully functional ribosomal subunits, ready to engage in translating mRNA into protein. This nucleolar function is accompanied by organization of the nucleolus into distinct subcompartments. In mammalian cells, nucleoli display three layers, nested like Russian dolls, where successive steps of ribosome production take place, starting

Tissue engineering strategies based on implanting cellularized biomaterials are promising therapeutic approaches for the reconstruction of large tissue defects. A major hurdle for the reliable establishment of such therapeutic approaches is the lack of rapid blood perfusion of the tissue construct to provide oxygen and nutrients. Numerous sources of mesenchymal stem cells (MSCs) displaying angiogenic potential have been characterized in the past years, including the adult dental pulp. Establishment of efficient strategies for improving angiogenesis in tissue constructs is nevertheless still an important challenge. Hypoxia was proposed as a priming treatment owing to its capacity to enhance the angiogenic potential of stem cells through vascular endothelial growth factor (VEGF) release. The present study aimed to characterize additional key factors regulating the angiogenic capacity of such MSCs, namely, dental pulp stem cells derived from deciduous teeth (SHED). We identified fibroblast growth factor-2 (FGF-2) as a potent inducer of the release of VEGF and hepatocyte growth factor (HGF) by SHED. We found that FGF-2 limited hypoxiainduced downregulation of HGF release. Using three-dimensional culture models of angiogenesis, we demonstrated that VEGF and HGF were both responsible for the high angiogenic potential of SHED through direct targeting of endothelial cells. In addition, FGF-2 treatment increased the fraction of Stro-1+/CD146+ progenitor cells. We then applied in vitro FGF-2 priming to SHED before encapsulation in hydrogels and in vivo subcutaneous implantation. Our results showed that FGF-2 priming is more efficient than hypoxia at increasing SHED-induced vascularization compared with nonprimed controls. Altogether, these data demonstrate that FGF-2 priming enhances the angiogenic potential of SHED through the secretion of both HGF and VEGF. STEM CELLS TRANSLATIONAL MEDICINE 2016;5:392-404 SIGNIFICANCEThe results from the present study show that fibroblast growth factor-2 (FGF-2) priming is more efficient than hypoxia at increasing dental pulp stem cells derived from deciduous teeth (SHED)-induced vascularization compared with nonprimed controls. Together, these data demonstrate that FGF-2 priming enhances the angiogenic potential of SHED through the secretion of both hepatocyte growth factor and vascular endothelial growth factor.