Hair follicle morphogenesis depends on Wnt, Shh, Notch, BMP and other signaling pathways interplay between epithelial and mesenchymal cells. The Wnt pathway plays an essential role during hair follicle induction, Shh is involved in morphogenesis and late stage differentiation, Notch signaling determines stem cell fate while BMP is involved in cellular differentiation. The Wnt pathway is considered to be the master regulator during hair follicle morphogenesis. Wnt signaling proceeds through EDA/EDAR/NF-κB signaling. NF-κB regulates the Wnt pathway and acts as a signal mediator by upregulating the expression of Shh ligand. Signal crosstalk between epithelial and mesenchymal cells takes place mainly through primary cilia. Primary cilia formation is initiated with epithelial laminin-511 interaction with dermal β-1 integrin, which also upregulates expression of downstream effectors of Shh pathway in dermal lineage. PDGF signal transduction essential for crosstalk is mediated through epithelial PDGF-A and PDGFRα expressed on the primary cilia. Dermal Shh and PDGF signaling up-regulates dermal noggin expression; noggin is a potent inhibitor of BMP signaling which helps in counteracting BMP mediated β-catenin inhibition. This interplay of signaling between the epithelial and dermal lineage helps in epithelial Shh signal amplification. The dermal Wnt pathway helps in upregulation of epithelial Notch expression. Dysregulation of these pathways leads to certain abnormalities and in some cases even tumor outgrowth.

Nestin is a type VI intermediate filament protein originally described in neural stem cells. Here we report that immature endothelial cells generated in the course of angiogenesis express nestin. Endothelial cells of embryonic capillaries destined to vascularize growing organs also express this intermediate filament protein. Whereas nestin was sporadically expressed in mature adult human endothelial cells sporadically express nestin, this protein was consistently expressed in adult angiogenic vasculature. Nestin expression was also detected in capillaries of the corpus luteum, which replenishes itself by angiogenesis. Nestin-immunoreactive vessels were also observed in the infarcted hearts where transient ischemia triggered regeneration accompanied with neovascularization of the myocardium. Nestinpositive endothelial cells lined vessels nourishing solid growing tumors, including melanoblastomas and glioblastomas. Our data provide definitive evidence that endothelial precursors express the neural stem cell marker nestin and that this protein participates in formation of the cytoskeleton of newly formed endothelial cells. Because nestin expression was recognized under all conditions of vascular development, nestin represents a novel and reliable marker of neovascularization.

Human prominin-1 (CD133) is expressed by various stem and progenitor cells originating from diverse sources. In addition to stem cells, its mouse ortholog is expressed in a broad range of adult epithelial cells, where it is selectively concentrated in their apical domain. The lack of detection of prominin-1 in adult human epithelia might be explained, at least in part, by the specificity of the widely used AC133 antibody, which recognizes an epitope that seems dependent on glycosylation. Here we decided to re-examine its expression in adult human tissues, particularly in glandular epithelia, using a novel monoclonal antibody (80B258) generated against the human prominin-1 polypeptide. In examined tissues, we observed 80B258 immunoreactivity at the apical or apicolateral membranes of polarized cells. For instance, we found expression in secretory serous and mucous cells as well as intercalated ducts of the large salivary and lacrimal glands. In sweat glands including the gland of Moll, 80B258 immunoreactivity was found in the secretory (eccrine and apocrine glands) and duct (eccrine glands) portion. In the liver, 80B258 immunoreactivity was identified in the canals of Hering, bile ductules, and small interlobular bile ducts. In the uterus, we detected 80B258 immunoreactivity in endometrial and cervical glands. Together these data show that the overall expression of human prominin-1 is beyond the rare primitive cells, and it seems to be a general marker of apical or apicolateral membrane of glandular epithelia. This manuscript contains online supplemental material at http://www.jhc.org . Please visit this article online to view these materials.

The lack of physiological parity between 2D cell culture and in vivo culture has led to the development of more organotypic models, such as organoids. Organoid models have been developed for a number of tissues, including the liver. Current organoid protocols are characterized by a reliance on extracellular matrices (ECMs), patterning in 2D culture, costly growth factors and a lack of cellular diversity, structure, and organization. Current hepatic organoid models are generally simplistic and composed of hepatocytes or cholangiocytes, rendering them less physiologically relevant compared to native tissue. We have developed an approach that does not require 2D patterning, is ECM independent, and employs small molecules to mimic embryonic liver development that produces large quantities of liver-like organoids. Using single-cell RNA sequencing and immunofluorescence, we demonstrate a liver-like cellular repertoire, a higher order cellular complexity, presenting with vascular luminal structures, and a population of resident macrophages: Kupffer cells. The organoids exhibit key liver functions, including drug metabolism, serum protein production, urea synthesis and coagulation factor production, with preserved post-translational modifications such as N-glycosylation and functionality. The organoids can be transplanted and maintained long term in mice producing human albumin. The organoids exhibit a complex cellular repertoire reflective of the organ and have de novo vascularization and liver-like function. These characteristics are a prerequisite for many applications from cellular therapy, tissue engineering, drug toxicity assessment, and disease modeling to basic developmental biology.

The designation NESTIN refers to a member of the family of intermediate filaments and comes from the fact that this protein is expressed mainly in neuroepithelial stem cells. However, nestin is not expressed in mature elements and terminal cell differentiation is associated with loss of immunoreactivity to this protein. Therefore, immunohistochemical assessment of nestin expression might be useful to differentiate between mature and immature elements. The aim of this study was to analyse nestin expression in various tumours of neuroectodermal and vascular origin and to determine whether its detection has practical relevance. The results indicate that the immunohistochemical detection of nestin expression could be useful in astrocytomas and malignant melanomas, where it could be used as an auxiliary indicator of dedifferentiation and progression. Because of the weak and heterogeneous expression of nestin in neurinomas, phaeochromocytomas, and carcinoids, nestin detection in these lesions is of little practical use.

Purpose: Mesenchymal stem cells isolated from bone marrow (BM-MSC) and periodontal ligament (PLSC) are cells with high proliferative potential and ability to self-renewal. Characterization of these cells under genotoxic stress conditions contributes to the assessment of their prospective usage. The aim of our study was to evaluate changes in BM-MSC and PLSC caused by ionizing radiation. Methods: Human BM-MSC and PLSC were irradiated with the doses up to 20 Gy by Co⁶⁰ and observed 13 days; viability, proliferation, apoptosis and senescence induction, and changes in expression and phosphorylation status of related proteins were studied. Results: Irradiation with the doses up to 20 Gy significantly reduces proliferation, but has no significant effect on cell viability. The activation of tumor suppressor protein 53 (p53) and its phosphorylations on serines 15 and 392 were detected from the first day after irradiation by 20 Gy and remained elevated to day 13. Expression of cyclin-dependent kinases inhibitor 1A (p21^Cip1/Waf1) increased. The cell cycle was arrested in G2 phase. Instead of apoptosis we have detected hallmarks of stress-induced premature senescence: increase in cyclin-dependent kinases inhibitor 2A (p16^INK4a) and increased activity of senescence-associated β-galactosidase. Conclusion: Mesenchymal stem cells isolated from bone marrow and periodontal ligament respond to ionizing radiation by induction of stress-induced premature senescence without apparent differences in their radiation response.