Intracellular Communication among Morphogen Signaling Pathways during Vertebrate Body Plan Formation

Engineering Programmable Material-To-Cell Pathways Via Synthetic Notch Receptors To Spatially Control Cellular Phenotypes In Multi-Cellular Constructs

Synthetic Notch (synNotch) receptors are modular synthetic components that are genetically engineered into mammalian cells to detect signals presented by neighboring cells and respond by activating prescribed transcriptional programs. To date, synNotch has been used to program therapeutic cells and pattern morphogenesis in multicellular systems. However, cell-presented ligands have limited versatility for applications that require spatial precision, such as tissue engineering. To address this, we developed a suite of materials to activate synNotch receptors and serve as generalizable platforms for generating user-defined material-to-cell signaling pathways. First, we demonstrate that synNotch ligands, such as GFP, can be conjugated to cell- generated ECM proteins via genetic engineering of fibronectin produced by fibroblasts. We then used enzymatic or click chemistry to covalently link synNotch ligands to gelatin polymers to activate synNotch receptors in cells grown on or within a hydrogel. To achieve microscale control over synNotch activation in cell monolayers, we microcontact printed synNotch ligands onto a surface. We also patterned tissues comprising cells with up to three distinct phenotypes by engineering cells with two distinct synthetic pathways and culturing them on surfaces microfluidically patterned with two synNotch ligands. We showcase this technology by co-transdifferentiating fibroblasts into skeletal muscle or endothelial cell precursors in user-defined spatial patterns towards the engineering of muscle tissue with prescribed vascular networks. Collectively, this suite of approaches extends the synNotch toolkit and provides novel avenues for spatially controlling cellular phenotypes in mammalian multicellular systems, with many broad applications in developmental biology, synthetic morphogenesis, human tissue modeling, and regenerative medicine.

Programmed ageing: decline of stem cell renewal, immunosenescence, and Alzheimer's disease

The characteristic maximum lifespan varies enormously across animal species from a few hours to hundreds of years. This argues that maximum lifespan, and the ageing process that itself dictates lifespan, are to a large extent genetically determined. Although controversial, this is supported by firm evidence that semelparous species display evolutionarily programmed ageing in response to reproductive and environmental cues. Parabiosis experiments reveal that ageing is orchestrated systemically through the circulation, accompanied by programmed changes in hormone levels across a lifetime. This implies that, like the circadian and circannual clocks, there is a master 'clock of age' (circavital clock) located in the limbic brain of mammals that modulates systemic changes in growth factor and hormone secretion over the lifespan, as well as systemic alterations in gene expression as revealed by genomic methylation analysis. Studies on accelerated ageing in mice, as well as human longevity genes, converge on evolutionarily conserved fibroblast growth factors (FGFs) and their receptors, including KLOTHO, as well as insulin-like growth factors (IGFs) and steroid hormones, as key players mediating the systemic effects of ageing. Age-related changes in these and multiple other factors are inferred to cause a progressive decline in tissue maintenance through failure of stem cell replenishment. This most severely affects the immune system, which requires constant renewal from bone marrow stem cells. Age-related immune decline increases risk of infection whereas lifespan can be extended in germfree animals. This and other evidence suggests that infection is the major cause of death in higher organisms. Immune decline is also associated with age-related diseases. Taking the example of Alzheimer's disease (AD), we assess the evidence that AD is caused by immunosenescence and infection. The signature protein of AD brain, Aβ, is now known to be an antimicrobial peptide, and Aβ deposits in AD brain may be a response to infection rather than a cause of disease. Because some cognitively normal elderly individuals show extensive neuropathology, we argue that the location of the pathology is crucial - specifically, lesions to limbic brain are likely to accentuate immunosenescence, and could thus underlie a vicious cycle of accelerated immune decline and microbial proliferation that culminates in AD. This general model may extend to other age-related diseases, and we propose a general paradigm of organismal senescence in which declining stem cell proliferation leads to programmed immunosenescence and mortality.

Gastrulation and Body Axes Formation: A Molecular Concept and Its Clinical Correlates

During the third week of human pregnancy, an embryo transforms from two germinal disc layers of hypoblast and epiblast to three germinal layers of endoderm, mesoderm and ectoderm. Gastrulation is a complex process that includes cellular mobility, morphogenesis and cell signalling, as well as chemical morphogenic gradients, transcription factors and differential gene expression. During gastrulation, many signalling channels coordinate individual cell actions in precise time and location. These channels control cell proliferation, shape, fate and migration to the correct sites. Subsequently, the anteroposterior (AP), dorsoventral (DV) and left-right (LR) body axes are formed before and during gastrulation via these signalling regulation signals. Hence, the anomalies in gastrulation caused by insults to certain molecular pathways manifest as a wide range of body axes-related disorders. This article outlines the formation of body axes during gastrulation and the anomalies as well as the clinical implications.

Extracellular Vesicles and Membrane Protrusions in Developmental Signaling

During embryonic development, cells communicate with each other to determine cell fate, guide migration, and shape morphogenesis. While the relevant secreted factors and their downstream target genes have been characterized extensively, how these signals travel between embryonic cells is still emerging. Evidence is accumulating that extracellular vesicles (EVs), which are well defined in cell culture and cancer, offer a crucial means of communication in embryos. Moreover, the release and/or reception of EVs is often facilitated by fine cellular protrusions, which have a history of study in development. However, due in part to the complexities of identifying fragile nanometer-scale extracellular structures within the three-dimensional embryonic environment, the nomenclature of developmental EVs and protrusions can be ambiguous, confounding progress. In this review, we provide a robust guide to categorizing these structures in order to enable comparisons between developmental systems and stages. Then, we discuss existing evidence supporting a role for EVs and fine cellular protrusions throughout development.

Zbtb21 is required for the anterior-posterior patterning of neural tissue in the early Xenopus embryo

The vertebrate body is organized along the dorsal-ventral (DV) and anterior-posterior (AP) axes by the BMP and Wnt pathways, respectively. We previously reported that Xenopus Zbtb14 promotes dorsalization (neural induction) of ectoderm by inhibiting BMP signaling and also posteriorizes neural tissue by activating Wnt signaling, thereby coordinating the patterning of the DV and AP axes during early development. Although it has been reported that human ZBTB21 binds to ZBTB14 and is involved in gene expression in cultured mammalian cells, the function of Zbtb21 in early embryonic development remains unknown. Here, we show that Xenopus Zbtb21 plays an essential role in AP axis formation in the early Xenopus embryo. zbtb21 and zbtb14 are co-expressed in the dorsal region of embryos during gastrulation. Simultaneous overexpression of Zbtb21 and Zbtb14 in ectodermal explants enhances the neural-inducing activity of Zbtb14. Moreover, knockdown experiments showed that Zbtb21 is required for the formation of posterior neural tissue and the suppression of anterior neural development. Collectively, these results suggest that in cooperation with Zbtb14, Zbtb21 has a crucial function in AP patterning during early Xenopus embryogenesis.

Primary cilia and PTH1R interplay in the regulation of osteogenic actions

Primary cilia are subcellular structures specialized in sensing different stimuli in a diversity of cell types. In bone, the primary cilium is involved in mechanical sensing and transduction of signals that regulate the behavior of mesenchymal osteoprogenitors, osteoblasts and osteocytes. To perform its functions, the primary cilium modulates a plethora of molecules including those stimulated by the parathyroid hormone (PTH) receptor type I (PTH1R), a master regulator of osteogenesis. Binding of the agonists PTH or PTH-related protein (PTHrP) to the PTH1R or direct agonist-independent stimulation of the receptor activate PTH1R signaling pathways. In turn, activation of PTH1R leads to regulation of bone formation and remodeling. Herein, we describe the structure, function and molecular partners of primary cilia in the context of bone, playing special attention to those signaling pathways that are mediated directly or indirectly by PTH1R in association with primary cilia during the process of osteogenesis.

Contribution of TWIST1-EVX1 Axis in Invasiveness of Esophageal Squamous Cell Carcinoma; a Functional Study

BACKGROUND

Epithelial-mesenchymal transition (EMT) is a biological process in embryonic development and cancer progression, and different gene families, such as HOX genes, are closely related to this process.

OBJECTIVES

Our aim in this study was to investigate the correlation between TWIST1 and EVX1 mRNA expression in ESCC patients and also examine the probable regulatory function of TWIST1 on EVX1 expression in human ESCC cell line.

MATERIALS AND METHODS

TWIST1 and EVX1 gene expression patterns were assessed in ESCC patients by relative comparative Real-time PCR then correlated with their clinical characteristics. In silico analysis of the EVX1 gene was conducted. KYSE-30 cells were transduced by a retroviral system to ectopically express TWIST1, followed by qRT-PCR to reveal the correlation between TWIST1 and EVX1 gene expression.

RESULTS

The expression of TWIST1 and EVX1 was correlated to each other significantly (p=0.005) in ESCC. Of 28 patients with under/normal expression of TWIST1, 22 samples (78.57%) had over/normal expression of EVX1. TWIST1 overexpression was correlated with advanced stages of the tumor (III, IV) (P = 0.019) and lymph node metastasis. However, EVX1 under expression was associated with lymph node metastasis (p = 0.027) and invasiveness of the disease (P = 0.037) in ESCC. Furthermore, retroviral transduction enforced significant overexpression of TWIST1 in GFP-hTWIST-1 approximately 9-fold compared to GFP control cells, causing a - 8.83- fold reduction in EVX1 mRNA expression significantly.

CONCLUSIONS

Our results indicated the repressive role of TWIST1 on EVX1 gene expression in ESCC. Therefore, our findings can help dissect the molecular mechanism of ESCC tumorigenesis and discover novel therapeutic targets for ESCC invasion and metastasis.

Growth Factor Roles in Soft Tissue Physiology and Pathophysiology

Repair and healing of injured and diseased tendons has been traditionally fraught with apprehension and difficulties, and often led to rather unsatisfactory results. The burgeoning research field of growth factors has opened new venues for treatment of tendon disorders and injuries, and possibly for treatment of disorders of the aorta and major arteries as well. Several chapters in this volume elucidate the role of transforming growth factor β (TGFß) in pathogenesis of several heritable disorders affecting soft tissues, such as aorta, cardiac valves, and tendons and ligaments. Several members of the bone morphogenetic group either have been approved by the FDA for treatment of non-healing fractures or have been undergoing intensive clinical and experimental testing for use of healing bone fractures and tendon injuries. Because fibroblast growth factors (FGFs) are involved in embryonic development of tendons and muscles among other tissues and organs, the hope is that applied research on FGF biological effects will lead to the development of some new treatment strategies providing that we can control angiogenicity of these growth factors. The problem, or rather question, regarding practical use of imsulin-like growth factor I (IGF-I) in tendon repair is whether IGF-I acts independently or under the guidance of growth hormone. FGF2 or platelet-derived growth factor (PDGF) alone or in combination with IGF-I stimulates regeneration of periodontal ligament: a matter of importance in Marfan patients with periodontitis. In contrast, vascular endothelial growth factor (VEGF) appears to have rather deleterious effects on experimental tendon healing, perhaps because of its angiogenic activity and stimulation of matrix metalloproteinases-proteases whose increased expression has been documented in a variety of ruptured tendons. Other modalities, such as local administration of platelet-rich plasma (PRP) and/or of mesenchymal stem cells have been explored extensively in tendon healing. Though treatment with PRP and mesenchymal stem cells has met with some success in horses (who experience a lot of tendon injuries and other tendon problems), the use of PRP and mesenchymal stem cells in people has been more problematic and requires more studies before PRP and mesenchymal stem cells can become reliable tools in management of soft tissue injuries and disorders.

The dual-specificity protein kinase Clk3 is essential for Xenopus neural development

During vertebrate development, the formation of the central nervous system (CNS) is initiated by neural induction and patterning of the embryonic ectoderm. We previously reported that Cdc2-like kinase 2 (Clk2) promotes neural development in Xenopus embryos by regulating morphogen signaling. However, the functions of other Clk family members and their roles in early embryonic development remain unknown. Here, we show that in addition to Clk2, Clk1 and Clk3 play a role in the formation of neural tissue in Xenopus. clk1 and clk3 are co-expressed in the developing neural tissue during early Xenopus embryogenesis. We found that overexpression of clk1 and clk3 increases the expression of neural marker genes in ectodermal explants. Furthermore, knockdown experiments showed that clk3 is required for the formation of neural tissues. These results suggest that Xenopus Clk3 plays an essential role in promoting neural development during early embryogenesis.

Familiar growth factors have diverse roles in neural network assembly

The assembly of neuronal circuits during development depends on guidance of axonal growth cones by molecular cues deposited in their environment. While a number of families of axon guidance molecules have been identified and reviewed, important and diverse activities of traditional growth factors are emerging. Besides clear and well recognized roles in the regulation of cell division, differentiation and survival, new research shows later phase roles for a number of growth factors in promoting neuronal migration, axon guidance and synapse formation throughout the nervous system.