The microenvironment patterns the pluripotent mouse epiblast through paracrine Furin and Pace4 proteolytic activities

The fate of pluripotent cells in early mouse embryos is controlled by graded Nodal signals that are activated by the endoproteases Furin and Pace4. Soluble forms of Furin and Pace4 cleave proNodal in vitro and after secretion in transfected cells, but direct evidence for paracrine activity in vivo is elusive. Here, we show that Furin and Pace4 are released by the extraembryonic microenvironment, and that they cleave a membrane-bound reporter substrate in adjacent epiblast cells and activate Nodal to maintain pluripotency. Secreted Pace4 and Furin also stimulated mesoderm formation, whereas endoderm was only induced by Pace4, correlating with a difference in the spatiotemporal distribution of these proteolytic activities. Our analysis of paracrine Furin and Pace4 activities and their in vivo functions significantly advances our understanding of how the epiblast is patterned by its microenvironment. Adding cell-cell communication to the pleiotropic portfolio of these proteases provides a new framework to study proprotein processing also in other relevant contexts.

A Novel 3D hydrogel based microfluidic cell culture platform

Keshav Krishnamani

Breakthroughs in health care over the coming decades may well consist of cell based therapeutics, potentially allowing the repair and replacement of damaged tissues and organs. Recently developed induced pluripotency methods as well as advances in stem cell biology show hope of such a reality. But such prospects come with the need to have a robust understanding and control over cell development and differentiation processes. Cells in the body develop in tightly controlled and specialized micro-environments that provide many complex cues and interactions that guide cell fate by directing gene expression. But current cell culture techniques that are most widely used to study the cell outside the body have not significantly changed from when first started over a century ago, using simple containers and flasks with plastic surfaces. Many studies have shown that three-dimensions (3D) over conventional 2D cell culture alone, showed to have increased levels of cell organization, morphology and function. By combining novel biomaterials and microfabrication methods, this project aims to create a tool that allows the study of cells within a simplified 3D environment. With the potential to build up the physical and soluble complexity of this environment in a tailor made fashion, a "dissection" of the functions and influences of external factors may be understood. Such a tool can also be used for the development of cell based models, highly relevant for drug discovery application as well as potentially for the development of cell based therapeutics. We have developed a novel microfluidic 3D cell culture platform that allows controlled soluble factor perfusion in an enzymatically formed and cell responsive PEG-based hydrogel. Soft lithographic processes were used to mold microchannels on a layer of hydrogel. In a second step, a flat hydrogel layer is placed on top to enclose and form the microchannels . The system allows the control over soluble factor delivery and it is able to perform long-term cell culture and generate user controlled gradients of soluble factors. With continuous perfusion, metabolic waste is constantly removed and cells are supplied with fresh medium. The platform also can allow creation of tailor made environments building up complexity in a controlled fashion. Higher throughput is also achieved by arraying individual culture chambers. The device was applied towards the culture of mouse embryonic stem cells (mESC) in order to demonstrate their self-renewal capacity on the microfluidic platform. The effects of some cytokine factors were also studied. Meaningful readouts such as fluorescence are easily used for analysis and cells can possibly be extracted from the device for further downstream analysis and processing. Through this device we show that microfluidics technologies combined with biomaterials enables the creation of platforms that are biologically relevant for the study and understanding of cell processes from cancer to stem cell development, processes which are fundamentally regulated by interactions with the microenvironment. The platform developed may also be used to develop human tissue models perhaps more relevant than current animal based testing, providing new tools for drug development and also potentially new approaches for developing cell based therapeutics

2009

Muscle stem cell's in vitro bipolar niche

Adrien de Tonnac

In the domain of regenerative medicine research there are many fronts aimed at increasing our understanding of induced pluripotent, embryonic and adult stem cells. Recently a new front has appeared, stem cell niches, the microenvironment that is a crucial component in the regulation of stem cells. New in vitro platforms are continually being created to answer the multitude of biological questions that surround stem cell niches. The transition from in vitro to in vivo is a heavy setback in cellular research due to a huge gap between the two conditions, which can only be reduced if the in vitro conditions better mimic those found in vivo. This project has reduced the gap and has the potential to continue minimizing the differences between the two conditions in the field of muscle stem cell research. Through a combination of the forefront techniques in biological research, we were able to create a new innovative bioengineered platform, a bipolar hydrogel microenvironment. First, we took advantage of polyethylene glycol (PEG) hydrogels, which are highly hydrophilic polymer networks that have properties that mimic physiologic tissue, including high water content and low Young's Modulus. Microfabrication techniques allowed us to topographically pattern the hydrogel at micro-dimensions resembling the native cell environment. Utilizing microfluidics and micro-printing techniques, the three-dimensional hydrogel surface was also patterned with tethered niche proteins found in the in vivo muscle stem cell niche. The swelling properties of the PEG hydrogel were considered as an advantage and controlled to form niche gaps with physical properties that were tuned to correspond to those found in vivo. This new complex and controlled surface for cells to be cultured on is a tool, which will allow biologists to probe new questions and gain insight into the regulatory networks that control cell fate

2009

Puromycin-sensitive aminopeptidase: Sequence analysis, expression, and functional characterization

Daniel Constam

Among the molecular mechanisms that control the cell division cycle, proteolysis has emerged as a key regulatory process enabling cells to pass critical check points. Such proteolysis involves a cascade of enzymes including a multisubunit complex termed 26S proteasome. Here we report on the analysis of a novel mouse cDNA encoding the puromycin-sensitive aminopeptidase (PSA) and on its expression in COS cells and 3T3 fibroblasts. PSA is 27-40% homologous to several known Zn(2+)-binding aminopeptidases including aminopeptidase N. Immunohistochemical analysis revealed that PSA is localized to the cytoplasm and to the nucleus and associates with microtubules of the spindle apparatus during mitosis. Furthermore, puromycin and bestatin both arrested the cell cycle, leading to an accumulation of cells in G2/M phase, and ultimately induced cells to undergo apoptosis at concentrations that inhibit PSA. Control experiments including cycloheximide further suggested that the induction of apoptosis by puromycin was not attributable to inhibition of protein synthesis. Taken together, these data favor the novel idea that PSA participates in proteolytic events essential for cell growth and viability.

American Society for Biochemistry and Molecular Biology1995

A Novel 3D hydrogel based microfluidic cell culture platform

Keshav Krishnamani

2009