Consider the marvel of the embryo. It begins as a glob of identical cells that change shape and function as they multiply to become the cells of our lungs, muscles, nerves and all the other specialized tissues of the body.
Now, in a feat of reverse tissue engineering, Stanford University researchers have begun to unravel the complex genetic coding that allows embryonic cells to proliferate and transform into all of the specialized cells that perform myriad biological tasks.
A team of interdisciplinary researchers took lung cells from the embryos of mice, choosing samples at different points in the development cycle. Using the new technique of single-cell genomic analysis, they recorded what genes were active in each cell at each point. Though they studied lung cells, their technique is applicable to any type of cell.
"This lays out a playbook for how to do reverse tissue engineering," said Stephen Quake, PhD, the Lee Otterson Professor in the School of Engineering and a Howard Hughes Medical Institute investigator.
The researchers' findings are described in a paper published online April 13 in Nature. Quake, who also is a professor of bioengineering and of applied physics, is the senior author. The lead authors are postdoctoral scholars Barbara Treutlein, PhD, and Doug Brownfield, PhD.
The researchers used the reverse-engineering technique to study the cells in the alveoli, the small, balloon-like structures at the tips of the airways in the lungs. The alveoli serve as docking stations where blood vessels receive oxygen and deliver carbon dioxide.
Treutlein and Brownfield isolated 198 lung cells from mouse embryos at three stages of gestation: 14.5 days, 16.5 days and 18.5 days (mice are usually born at 20 days). They also took some lung cells from adult mice.
They used standard enzymatic techniques to dissolve the proteins that hold the lung cells together in tissue form, then sorted out the specific alveolar cell types that were the focus of their study.
Their next steps involved newer techniques at the heart of their reverse-engineering process.
Recall how eyedroppers work. Squeeze the rubber bulb to evacuate the air; plunge it into a solution to fill it with fluid; squeeze the bulb again to force the fluid out. In recent years, biotechnologists have used those basic principles to develop microfluidic devices of such precision that they can suck a single cell out of solution and isolate it in a chamber to study its genetic material.
Quake's lab has pioneered the use of microfluidic devices to study single cells. In this study, they used microfluidic devices to capture their 198 sample lung cells. Then they used single-cell genomic sequencing to measure which genes were active in each cell at each time.
How did they decode genomic activity in a single cell? DNA in the nucleus of every cell contains the full genome for that organism. That's why it's possible to build an organism from a single cell. But only some of those genes are active in any given cell at any given time. That's why lung cells are different than hair cells; each cell has a different set of active genes directing its functions.
Genes direct cellular activity by making or "expressing" messenger RNA. Each mRNA instructs the cell to make a particular protein. Cells are essentially a group of interacting proteins. Therefore knowing which mRNAs are active offers a lens into the function of that cell at the point when it was captured in the microfluidic device.
Using this process the Stanford researchers revealed for the first time precisely which genes regulate the development of these particular lung cells at each step along the way to mature alveoli.
One important finding involved the development of two key cell types at the tip of the alveoli, where the lung meets blood to perform the gas exchange that keeps us alive.
Alveolar type-1 cells are the flattest cells in the body. Blood cells dock alongside them to deliver oxygen or pick up carbon dioxide. The thinness of the cell is vital to facilitating this gas transfer.
Alveolar type-2 cells are compact and cuboidal. They secrete proteins to keep the alveoli from collapsing like empty balloons, so as to maintain the inner space through which oxygen and carbon dioxide can move.
Using single-cell genomics allowed the researchers to reverse engineer the development process to show how a single progenitor cell type gives rise to both of these different, mature alveolar cells.
The researchers also captured cells in transition from the progenitor to mature cell state, gaining crucial insights into the mechanism of alveolar cell differentiation.
Although this study focused on lung cells, the technique — capturing individual cells at different stages of embryonic development and assessing gene activity through mRNA sequencing — can be used to reverse-engineer other tissues.
In addition to studying embryonic development, the technique could be used in clinical settings. For instance, researchers could study differences between individual cells in a tumor, improving our understanding of the stages of cancers and leading to better, more targeted therapies.
"This technology represents a quantal leap forward in our ability to apprehend the full diversity of cell types in a given population, including rare ones that could have special functions," said Tushar Desai, MD, MPH, assistant professor of pulmonary and critical care medicine at Stanford and co-author of the paper. "Because a comprehensive molecular characterization of each type is achieved, including the signals they send and receive, a snapshot of the communication between individual cells will also emerge and may suggest attractive therapeutic targets in disease."
The other Stanford co-authors of the paper are Mark Krasnow, MD, PhD, professor of biochemistry and an HHMI investigator; postdoctoral scholar Angela Wu, PhD; Norma Neff, PhD, genomics core director in the Department of Bioengineering; research assistant Gary Mantalas; and F. Hernan Espinoza, PhD, an HHMI research specialist.
The research was supported by the National Heart Lung and Blood Institute, the National Institutes of Health, the Parker B. Francis Foundation and the Howard Hughes Medical Institute.
The work was also supported by the Department of Bioengineering, which is jointly operated by the School of Engineering and the School of Medicine.
The Stanford University School of Medicine consistently ranks among the nation's top medical schools, integrating research, medical education, patient care and community service. For more news about the school, please visit http://mednews.stanford.edu. The medical school is part of Stanford Medicine, which includes Stanford Hospital & Clinics and Lucile Packard Children's Hospital Stanford. For information about all three, please visit http://stanfordmedicine.org/about/news.html.
The Stanford School of Engineering has been at forefront of innovation for nearly a century, creating pivotal technologies and businesses that have transformed the worlds of technology, medicine, energy and communications and laid the foundation for Silicon Valley. The school advances modern science and engineering through teaching and research. The school is home to nine departments, 245 faculty and more than 4,000 students, tackling the world's most pressing problems in areas like human health and environmental sustainability. For more information, visit http://engineering.stanford.edu.
Tom Abate | Eurek Alert!
MACC1 Gene Is an Independent Prognostic Biomarker for Survival in Klatskin Tumor Patients
31.08.2015 | Max-Delbrück-Centrum für Molekulare Medizin in der Helmholtz-Gemeinschaft
Fish Oil-Diet Benefits May be Mediated by Gut Microbes
28.08.2015 | University of Gothenburg
Longer, more severe, and hotter droughts and a myriad of other threats, including diseases and more extensive and severe wildfires, are threatening to transform some of the world's temperate forests, a new study published in Science has found. Without informed management, some forests could convert to shrublands or grasslands within the coming decades.
"While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease...
A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.
The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...
A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).
Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...
In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.
These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...
Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.
For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...
20.08.2015 | Event News
20.08.2015 | Event News
19.08.2015 | Event News
31.08.2015 | Awards Funding
31.08.2015 | Materials Sciences
31.08.2015 | Materials Sciences