Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Urgent! How genes tell cellular construction crews, 'Read me now!'

14.08.2013
Stowers researchers show that DNA sequences at the beginning of genes -- at least in fruit flies -- contain more information than previously thought

When egg and sperm combine, the new embryo bustles with activity. Its cells multiply so rapidly they largely ignore their DNA, other than to copy it and to read just a few essential genes. The embryonic cells mainly rely on molecular instructions placed in the egg by its mother in the form of RNA.


The dorsal-ventral patterning gene snail (shown in red) is one of the few genes that are active before as well as after the midblastula transition. The segmentation gene paired (shown in green) is turned on during the transition. Cell nuclei are shown in blue.

Credit: Image: Courtesy of Kai Chen

The cells translate these RNA molecules into proteins that manage almost everything in the first minutes or hours of the embryo's life. Then, during the so-called midblastula transition, cells start transcribing massive amounts of their own DNA. How embryonic cells prepare for this moment, and how they flag a small set of genes for transcription before that, holds important information about normal development and disease in animals and in humans.

A new study that sheds light on these questions appears in the Aug. 13 issue of eLife Sciences, authored by researchers at the Stowers Institute for Medical Research. The team, led by Associate Investigator Julia Zeitlinger, Ph.D., shows that in the fruit fly Drosophila melanogaster, genes active in the first two hours of a fertilized egg are read quickly due to special instructions at the beginning of each gene, in a region aptly named the "promoter."

Within each promoter region, different combinations of short control elements or "boxes" form a code that instructs specialized construction crews, called RNA polymerases, where and when to start transcribing. Researchers long thought that once an RNA polymerase appears at the worksite it would quickly finish the job.

"The most important result is that promoters are different," Zeitlinger says. "The general paradigm for a long time has been a promoter is a promoter. But really what we see is that they have different functions."

As a postdoctoral fellow at MIT, Zeitlinger unexpectedly discovered that sometimes RNA polymerase II pauses at the beginning of a gene as if taking a lunch break. More often than not, pausing occurred at genes important for development. Zeitlinger thought pausing may help get these molecular construction workers on site before a huge work order is due.

"We were wondering whether pausing was being used for preparing global gene activation during the midblastula transition," says Kai Chen, PhD, a former graduate student in Zeitlinger's lab and the study's first author. "We expected to see widespread pausing before that transition."

The fruit fly Drosophila melanogaster was a perfect test subject. This fly embryo takes two hours to reach the midblastula transition providing plenty of time to analyze what happens during this early period. Furthermore, decades of previous research on the flies provided context to guide the work.

Chen used a method called ChIP-seq, which can locate RNA polymerase II molecules on any gene. Paused polymerases would show up only at the beginning of genes. Working polymerases, on the other hand, would be found throughout the gene body.

The results took the Stowers team by surprise. Before the midblastula transition, RNA Polymerase II appeared to rarely pause as it transcribed roughly 100 early genes. And no construction crews were sitting idle on inactive genes in preparation for the midblastula transition. Pausing only became widespread only during the midblastula transition itself.

"What we found was not what we expected at all," Zeitlinger says. Before the midblastula transition, instead of preparing for a huge workload the construction crews were busy completing rush jobs. "The polymerase has to come to the promoter and immediately transcribe because there's so little time to do the job. That's one way of making transcription faster. "

When Chen and colleagues computationally compared the DNA sequences of promoters where pausing occurred with those where it didn't, a pattern emerged. They found that three different types of promoters correlated with the construction crew's pausing behavior.

The genes that RNA Polymerase II reads before the midblastula transition were often preceded by a promoter that seemed to yell, "Urgent! Don't even think about pausing." These promoters contain what's known as a TATA-box, named for its conserved arrangement of nucleotides, most commonly TATAA.

As cell division slows down during the midblastula transition, cells have the luxury of pausing, perhaps to fine-tune when transcription begins, Zeitlinger says.

These midblastula genes were regulated by promoters that contain a variety of specific promoter elements associated with paused RNA polymerase, including GAGA, Downstream Promoter Element (DPE), Motif Two Element (MTF) and Pause Button (PB).

The team also found a third type of promoter, which contained both the TATA-box and the pausing sequences. At these genes, RNA polymerase II does not pause initially but begins to pause during the midblastula transition.

Zeitlinger hopes learning more about promoters will give clues to the functions of unknown genes. Because these promoter sequences are not specific to flies, the differences among promoter types may be conserved in other animals as well.

"My lab is interested in understanding how development or even diseases are encoded in the genome," Zeitlinger says. "If we understand transcription, then we can predict a lot of what genomes encode, in terms of disease or differences between individuals."

"Promoters had been seen by some scientists as sort of boring," she adds, "but now, they are starting to get really interesting."

Other contributors include Jeff Johnston, Wanqing Shao, Samuel Meier and Cynthia Staber, all from the Stowers Institute.

The study was funded by the Stowers Institute for Medical Research, the Pew Charitable Trust and an NIH New Innovator Award.

About the Stowers Institute for Medical Research

The Stowers Institute for Medical Research is a non-profit, basic biomedical research organization dedicated to improving human health by studying the fundamental processes of life. Jim Stowers, founder of American Century Investments, and his wife Virginia opened the Institute in 2000. Since then, the Institute has spent over 900 million dollars in pursuit of its mission.

Currently the Institute is home to nearly 550 researchers and support personnel; over 20 independent research programs; and more than a dozen technology development and core facilities. Learn more about the Institute at http://www.stowers.org.

Gina Kirchweger | EurekAlert!
Further information:
http://www.stowers.org

More articles from Life Sciences:

nachricht Newly designed molecule binds nitrogen
23.02.2018 | Julius-Maximilians-Universität Würzburg

nachricht Atomic Design by Water
23.02.2018 | Max-Planck-Institut für Eisenforschung GmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>