The lymphatic system plays a key role in tissue fluid regulation and tumour metastasis, and lymphatic defects underlie many pathological states including lymphoedema, lymphangiectasia, lymphangioma and lymphatic dysplasia. However, the origins of the lymphatic system in the embryo, and the mechanisms that direct growth of the network of lymphatic vessels, remain unclear. Lymphatic vessels are thought to arise from endothelial precursor cells budding from the cardinal vein under the influence of the lymphatic hallmark gene Prox1 (prospero homeobox 1; ref. 4). Defects in the transcription factor gene SOX18 (SRY (sex determining region Y) box 18) cause lymphatic dysfunction in the human syndrome hypotrichosis-lymphoedema-telangiectasia, suggesting that Sox18 may also play a role in lymphatic development or function. Here we use molecular, cellular and genetic assays in mice to show that Sox18 acts as a molecular switch to induce differentiation of lymphatic endothelial cells. Sox18 is expressed in a subset of cardinal vein cells that later co-express Prox1 and migrate to form lymphatic vessels. Sox18 directly activates Prox1 transcription by binding to its proximal promoter. Overexpression of Sox18 in blood vascular endothelial cells induces them to express Prox1 and other lymphatic endothelial markers, while Sox18-null embryos show a complete blockade of lymphatic endothelial cell differentiation from the cardinal vein. Our findings demonstrate a critical role for Sox18 in developmental lymphangiogenesis, and suggest new avenues to investigate for therapeutic management of human lymphangiopathies.

The Wnt/beta-catenin pathway is evolutionary conserved signaling system that regulates cell differentiation and organogenesis. We show that endothelial specific stabilization of Wnt/beta-catenin signaling alters early vascular development in the embryo. The phenotype resembles that induced by upregulation of Notch signaling, including lack of vascular remodeling, altered elongation of the intersomitic vessels, defects in branching, and loss of venous identity. Both in vivo and in vitro data show that beta-catenin upregulates Dll4 transcription and strongly increases Notch signaling in the endothelium, leading to functional and morphological alterations. The functional consequences of beta-catenin signaling depend on the stage of vascular development and are lost when a gain-of-function mutation is induced at a late stage of development or postnatally. Our findings establish a link between Wnt and Notch signaling in vascular development. We propose that early and sustained beta-catenin signaling prevents correct endothelial cell differentiation, altering vascular remodeling and arteriovenous specification.

Self-assembling peptides (SAPs) are rapidly gaining interest as bioinspired scaffolds for cell culture and regenerative medicine applications. Bone Marrow Homing Peptide 1 (BMHP1) functional motif (PFSSTKT) was previously demonstrated to stimulate neural stem cell (NSC) viability and differentiation when linked to SAPs. We here describe a novel ensemble of SAPs, developed from the BMHP1 (BMHP1-SAPs), that spontaneously assemble into tabular fibers, twisted ribbons, tubes and hierarchical self-assembled sheets: organized structures in the nano- and microscale. Thirty-two sequences were designed and evaluated, including biotinylated and unbiotinylated sequences, as well as a hybrid peptide-peptoid sequence. Via X-ray diffraction (XRD), CD, and FTIR experiments we demonstrated that all of the BMHP1-SAPs share similarly organized secondary structures, that is, β-sheets and β-turns, despite their heterogeneous nanostructure morphology, scaffold stiffness, and effect over NSC differentiation and survival. Notably, we demonstrated the self-healing propensity of most of the tested BMHP1-SAPs, enlarging the set of potential applications of these novel SAPs. In in vitro cell culture experiments, we showed that some of these 10-mer peptides foster adhesion, differentiation, and proliferation of human NSCs. RGD-functionalized and hybrid peptide-peptoid self-assembling sequences also opened the door to BMHP1-SAP functionalization with further bioactive motifs, essential to tailor new scaffolds for specific applications. In in vivo experiments we verified a negligible reaction of the host nervous tissue to the injected and assembled BMHP1-SAP. This work will pave the way to the development of novel SAP sequences that may be useful for material science and regenerative medicine applications.

Nanostructured scaffolds recently showed great promise in tissue engineering: nanomaterials can be tailored at the molecular level and scaffold morphology may more closely resemble features of extracellular matrix components in terms of porosity, framing and biofunctionalities. As a consequence, both biomechanical properties of scaffold microenvironments and biomaterial-protein interactions can be tuned, allowing for improved transplanted cell engraftment and better controlled diffusion of drugs. Easier said than done, a nanotech-based regenerative approach encompasses different fields of know-how, ranging from in silico simulations, nanomaterial synthesis and characterization at the nano-, micro- and mesoscales to random library screening methods (e.g. phage display), in vitro cellular-based experiments and validation in animal models of the target injury. All of these steps of the "assembly line" of nanostructured scaffolds are tightly interconnected both in their standard analysis techniques and in their most recent breakthroughs: indeed their efforts have to jointly provide the deepest possible analyses of the diverse facets of the challenging field of neural tissue engineering. The purpose of this review is therefore to provide a critical overview of the recent advances in and drawbacks and potential of each mentioned field, contributing to the realization of effective nanotech-based therapies for the regeneration of peripheral nerve transections, spinal cord injuries and brain traumatic injuries. Far from being the ultimate overview of such a number of topics, the reader will acknowledge the intrinsic complexity of the goal of nanotech tissue engineering for a conscious approach to the development of a regenerative therapy and, by deciphering the thread connecting all steps of the research, will gain the necessary view of its tremendous potential if each piece of stone is correctly placed to work synergically in this impressive mosaic.