Matrix elasticity of void-forming hydrogels controls transplanted-stem-cell-mediated bone formation

The effectiveness of stem cell therapies has been hampered by cell death and limited control over fate. These problems can be partially circumvented by using macroporous biomaterials that improve the survival of transplanted stem cells and provide molecular cues to direct cell phenotype. Stem cell behaviour can also be controlled in vitro by manipulating the elasticity of both porous and non-porous materials, yet translation to therapeutic processes in vivo remains elusive. Here, by developing injectable, void-forming hydrogels that decouple pore formation from elasticity, we show that mesenchymal stem cell (MSC) osteogenesis in vitro, and cell deployment in vitro and in vivo, can be controlled by modifying, respectively, the hydrogel’s elastic modulus or its chemistry. When the hydrogels were used to transplant MSCs, the hydrogel’s elasticity regulated bone regeneration, with optimal bone formation at 60 kPa. Our findings show that biophysical cues can be harnessed to direct therapeutic stem cell behaviours in situ

Expression of the transcription factor, TFII-I, during post-implantation mouse embryonic development

<p>Abstract</p> <p>Background</p> <p>General transcription factor (TFII-I) is a multi-functional transcription factor encoded by the Gtf2i gene, that has been demonstrated to regulate transcription of genes critical for development. Because of the broad range of genes regulated by TFII-I as well as its potential role in a significant neuro-developmental disorder, developing a comprehensive expression profile is critical to the study of this transcription factor. We sought to define the timing and pattern of expression of TFII-I in post-implantation embryos at a time during which many putative TFII-I target genes are expressed.</p> <p>Findings</p> <p>Antibodies to the N-terminus of TFII-I were used to probe embryonic mouse sections. TFII-I protein is widely expressed in the developing embryo. TFII-I is expressed throughout the period from E8-E16. However, within this period there are striking shifts in localization from cytoplasmic predominant to nuclear. TFII-I expression varies in both a spatial and temporal fashion. There is extensive expression in neural precursors at E8. This expression persists at later stages. TFII-I is expressed in developing lung, heart and gut structures. There is no evidence of isoform specific expression. Available data regarding expression patterns at both an RNA and protein level throughout development are also comprehensively reviewed.</p> <p>Conclusions</p> <p>Our immunohistochemical studies of the temporal and spatial expression patterns of TFII-I in mouse embryonic sections are consistent with the hypothesis that hemizygous deletion of <it>GTF2I </it>in individuals with Williams-Beuren Syndrome contributes to the distinct cognitive and physiological symptoms associated with the disorder.</p

Cell-Sorting at the A/P Boundary in the Drosophila Wing Primordium: A Computational Model to Consolidate Observed Non-Local Effects of Hh Signaling

Non-intermingling, adjacent populations of cells define compartment boundaries; such boundaries are often essential for the positioning and the maintenance of tissue-organizers during growth. In the developing wing primordium of Drosophila melanogaster, signaling by the secreted protein Hedgehog (Hh) is required for compartment boundary maintenance. However, the precise mechanism of Hh input remains poorly understood. Here, we combine experimental observations of perturbed Hh signaling with computer simulations of cellular behavior, and connect physical properties of cells to their Hh signaling status. We find that experimental disruption of Hh signaling has observable effects on cell sorting surprisingly far from the compartment boundary, which is in contrast to a previous model that confines Hh influence to the compartment boundary itself. We have recapitulated our experimental observations by simulations of Hh diffusion and transduction coupled to mechanical tension along cell-to-cell contact surfaces. Intriguingly, the best results were obtained under the assumption that Hh signaling cannot alter the overall tension force of the cell, but will merely re-distribute it locally inside the cell, relative to the signaling status of neighboring cells. Our results suggest a scenario in which homotypic interactions of a putative Hh target molecule at the cell surface are converted into a mechanical force. Such a scenario could explain why the mechanical output of Hh signaling appears to be confined to the compartment boundary, despite the longer range of the Hh molecule itself. Our study is the first to couple a cellular vertex model describing mechanical properties of cells in a growing tissue, to an explicit model of an entire signaling pathway, including a freely diffusible component. We discuss potential applications and challenges of such an approach

Molecular and cellular mechanisms underlying the evolution of form and function in the amniote jaw.

The amniote jaw complex is a remarkable amalgamation of derivatives from distinct embryonic cell lineages. During development, the cells in these lineages experience concerted movements, migrations, and signaling interactions that take them from their initial origins to their final destinations and imbue their derivatives with aspects of form including their axial orientation, anatomical identity, size, and shape. Perturbations along the way can produce defects and disease, but also generate the variation necessary for jaw evolution and adaptation. We focus on molecular and cellular mechanisms that regulate form in the amniote jaw complex, and that enable structural and functional integration. Special emphasis is placed on the role of cranial neural crest mesenchyme (NCM) during the species-specific patterning of bone, cartilage, tendon, muscle, and other jaw tissues. We also address the effects of biomechanical forces during jaw development and discuss ways in which certain molecular and cellular responses add adaptive and evolutionary plasticity to jaw morphology. Overall, we highlight how variation in molecular and cellular programs can promote the phenomenal diversity and functional morphology achieved during amniote jaw evolution or lead to the range of jaw defects and disease that affect the human condition

Conserving, Distributing and Managing Genetically Modified Mouse Lines by Sperm Cryopreservation

Sperm from C57BL/6 mice are difficult to cryopreserve and recover. Yet, the majority of genetically modified (GM) lines are maintained on this genetic background.Reported here is the development of an easily implemented method that consistently yields fertilization rates of 70+/-5% with this strain. This six-fold increase is achieved by collecting sperm from the vas deferens and epididymis into a cryoprotective medium of 18% raffinose (w/v), 3% skim milk (w/v) and 477 microM monothioglycerol. The sperm suspension is loaded into 0.25 mL French straws and cooled at 37+/-1 degrees C/min before being plunged and then stored in LN(2). Subsequent to storage, the sperm are warmed at 2,232+/-162 degrees C/min and incubated in in vitro fertilization media for an hour prior to the addition of oocyte cumulus masses from superovulated females. Sperm from 735 GM mouse lines on 12 common genetic backgrounds including C57BL/6J, BALB/cJ, 129S1/SvImJ, FVB/NJ and NOD/ShiLtJ were cryopreserved and recovered. C57BL/6J and BALB/cByJ fertilization rates, using frozen sperm, were slightly reduced compared to rates involving fresh sperm; fertilization rates using fresh or frozen sperm were equivalent in all other lines. Developmental capacity of embryos produced using cryopreserved sperm was equivalent, or superior to, cryopreserved IVF-derived embryos.Combined, these results demonstrate the broad applicability of our approach as an economical and efficient option for archiving and distributing mice

Epoxyeicosanoids promote organ and tissue regeneration

Epoxyeicosatrienoic acids (EETs), lipid mediators produced by cytochrome P450 epoxygenases, regulate inflammation, angiogenesis, and vascular tone. Despite pleiotropic effects on cells, the role of these epoxyeicosanoids in normal organ and tissue regeneration remains unknown. EETs are produced predominantly in the endothelium. Normal organ and tissue regeneration require an active paracrine role of the microvascular endothelium, which in turn depends on angiogenic growth factors. Thus, we hypothesize that endothelial cells stimulate organ and tissue regeneration via production of bioactive EETs. To determine whether endothelial-derived EETs affect physiologic tissue growth in vivo, we used genetic and pharmacological tools to manipulate endogenous EET levels. We show that endothelial-derived EETs play a critical role in accelerating tissue growth in vivo, including liver regeneration, kidney compensatory growth, lung compensatory growth, wound healing, corneal neovascularization, and retinal vascularization. Administration of synthetic EETs recapitulated these results, whereas lowering EET levels, either genetically or pharmacologically, delayed tissue regeneration, demonstrating that pharmacological modulation of EETs can affect normal organ and tissue growth. We also show that soluble epoxide hydrolase inhibitors, which elevate endogenous EET levels, promote liver and lung regeneration. Thus, our observations indicate a central role for EETs in organ and tissue regeneration and their contribution to tissue homeostasis