Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

One shot: A molecular movie of events that enable sperm to penetrate egg’s coating

06.09.2005


Researchers have capitalized on the unique properties of a sperm cell to follow cell membrane fusion as it occurs during fertilization, tracking the full cascade of events for the first time. The findings could reveal new ways to enhance or block fertilization, as well as how to control the secretion of neurotransmitters and hormones such as insulin.



Luis Mayorga, a Howard Hughes Medical Institute (HHMI) international research scholar, and colleagues at the National University of Cuyo School of Medicine in Mendoza, Argentina, took advantage of the cellular specialization that gives sperm one irreversible chance to fertilize an egg.

The group followed the sperm’s secretion of the enzymes used to penetrate the protective outer coating that surrounds an egg. "Because the sperm has a single opportunity, this secretion has to be very well-regulated," said Mayorga. "If the sperm doesn’t respond right on time, it won’t get through the egg’s coating." And since fertilization is one-way and all-or-nothing, so too is the fusion event that releases the sperm’s enzymes. This tight control enabled Mayorga’s laboratory to capture a molecular movie of fusion as it unfolded. Their findings will be published in the September issue of the journal Public Library of Science Biology.


Inside the sperm, the enzymes are contained in a small bag known as the acrosome. During fertilization, as the acrosome membrane meets the sperm’s outer membrane, the two fuse together, and the enzymes are released outside the cell – much the same way a bubble rises to the surface of a soda and releases its gas into the air.

Mayorga, who has studied membrane fusion for more than 15 years, recognized an unexplored potential in this simple secretion event, called acrosomal exocytosis (AE). Preliminary experiments showed that AE uses the same basic fusion molecules as neuronal and endocrine cells. However, AE is much less complicated than fusion in these other cell types because it only happens once; other cells secrete the same substances again and again, requiring the fusion machinery to recycle multiple times.

The team evaluated the molecules that bring membranes together to fuse. These molecules, called SNAREs, work somewhat like Velcro to hold membranes in close enough proximity to merge. In sperm, the acrosome membrane containing the enzymes has one type of SNARE and the sperm’s outer membrane has another.

In the beginning, the acrosome SNAREs are stuck to each other and the outer membrane SNAREs are stuck to each other in what are called cis-SNARE pairs. These must be broken apart so that acrosome SNAREs can pair with outer membrane SNAREs in trans-SNARE pairs. When a sperm encounters the egg surface, calcium is released into the sperm cell, which triggers molecules that break apart the cis-SNARE pairs.

The Argentine scientists found that immediately after this step, loose trans-SNARE pairs form between the acrosome membrane and the sperm outer membrane. Such loose SNARE formations have been hypothesized but never shown directly. Mayorga’s group treated the trans-SNARE formations with toxins before the final stage of fusion and found that some, but not all, of the toxins inhibited the process. This indicated that the SNAREs were neither completely unpaired, which would make them most susceptible to toxins, nor were they clamped together in their final, tight configuration, which would make them resistant to toxins.

Then the researchers found that the final, tight trans-SNARE pairs form after more calcium is released from inside the acrosome. Once the acrosome membrane is locked to the outer membrane of the sperm by these tight pairs, a fusion factor causes the two membranes to fuse together, forming a pore that releases the enzymes outside the sperm where they can begin to digest the coating that surrounds the egg.

"In our experiments, it is very clear that those complexes have a loose form and are waiting for calcium to complete fusion," said Mayorga. "We show step-by-step how membrane fusion is really occurring in acrosomal exocytosis."

Many of the factors involved in AE will be important for manipulating fertilization--either to enhance it or block it, Mayorga said. Knowing the exact steps in the sperm’s simple AE system could also help researchers working on the more complicated membrane fusion processes that are critical for proper cell divisions, infection of cells by bacteria and viruses, and secretion of hormones and neurotransmitters.

"The field is very actively searching for ways to regulate exocytosis--to regulate the insulin-producing beta cells of the pancreas to prevent diabetes or to get neurotransmitters released in the brain at the right time or concentration," Mayorga pointed out. "Those are all examples of regulated exocytosis, and AE is a simple model they can use."

Cindy Fox Aisen | EurekAlert!
Further information:
http://www.hhmi.org

More articles from Life Sciences:

nachricht Researchers develop eco-friendly, 4-in-1 catalyst
25.04.2017 | Brown University

nachricht Transfecting cells gently – the LZH presents a GNOME prototype at the Labvolution 2017
25.04.2017 | Laser Zentrum Hannover e.V.

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

NASA's Fermi catches gamma-ray flashes from tropical storms

25.04.2017 | Physics and Astronomy

Researchers invent process to make sustainable rubber, plastics

25.04.2017 | Materials Sciences

Transfecting cells gently – the LZH presents a GNOME prototype at the Labvolution 2017

25.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>