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 Two Group A Streptococcus genes linked to 'flesh-eating' bacterial infections
25.09.2017 | University of Maryland

nachricht Rainbow colors reveal cell history: Uncovering β-cell heterogeneity
22.09.2017 | DFG-Forschungszentrum für Regenerative Therapien TU Dresden

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

An international team of physicists a coherent amplification effect in laser excited dielectrics

25.09.2017 | Physics and Astronomy

LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

25.09.2017 | Trade Fair News

Highest-energy cosmic rays have extragalactic origin

25.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>