This blog is currently on hiatus owing to work commitments. Whilst I still keep an eye on the goings on at RiAus, and contribute to the work of the good folks at eLife, little will be added to this blog for the foreseeable future. Simon Says remains open for business, albeit at a reduced capacity. Thanks for stopping by, and I hope the archive of content found here will prove to be of interest.

Monday, 24 June 2013

Monday Science: On Carrots, Cake and Sperm

It’s the carrot in front of the mule and the cake in front of the child: individuals are drawn to reward. But surround them by that reward — a mule in a field of carrots, a child in a cake shop — and behaviour switches from unidirectional to hyperactive. The greyhound that focuses on the moving rabbit wins the race: the greyhound that gets distracted by rabbits in the field next door may one day reach the finish line, but not because of the lure.

So it is in biology. Chemotaxis, the process by which cells and bacteria move according to certain chemicals in their surroundings, relies on a gradient of attractive or repulsive cues to cause directed movement. Surround a cell by growth factors and it will grow in all directions, but form a gradient in one direction only and it will grow that way. This is how nerves form complicated networks throughout the body, wrapping around other structures, and it is how good sperm find an egg.

More than 70 million couples globally are affected by infertility, of which at least half are due to the inability of sperm to fertilize the egg. This is because sperm quality per sample is usually highly variable, with many mutated cells and poor swimmers.

Despite technological advances, fertility treatment remains inefficient, with about a 30% success rate. The hurdle of poor sperm quality has not been overcome. Fertility treatment is also expensive and has a deep emotional cost.

Now, researchers at the Universidad de C√≥rdoba in Argentina have developed a method for separating good sperm from poor sperm, offering hope for the improvement of assisted reproductive technology, and it’s all down to that single carrot, dangled before the mule.

Egg cells mature within a cluster of cells called cumulus cells, which are essential for the egg’s development and protection. One of the many jobs of the cumulus cells is to kick out the steroid hormone progesterone. Sperm react positively to gradients of very low amounts of progesterone, but, like the child in a cake shop, go wild if surrounded by too much. It also happens that the cells that respond most efficiently, and less chaotically, to the very lowest concentrations of progesterone are the very best sperm, the ones that would, given the opportunity, competently fertilize an egg. This new study from the laboratory of Prof Laura Giojalas takes advantage of this behaviour.

Their device, called the sperm selection assay (SSA), takes only 20 minutes to operate, using a low concentration progesterone gradient between two small plastic dishes, between which the sperm swim. After this time, the collected sample contained three times as many high quality sperm cells than both normal and poor quality starting samples. In addition, with only a 20 minute run time, the experiment can be repeated to further improve sample quality. Purified sperm from the SSA also had reduced DNA damage.

The SSA was particularly effective when run on extremely poor quality starting samples, where the level of high quality cells could be increased by up to 11 times.

These are still early days — having more good cells per sample still does not guarantee fertilization — but the SSA is a helpful step towards overcoming this hurdle in human fertility treatment.

Gatica, L. V. et al. Picomolar gradients of progesterone select functional human sperm even in subfertile samples. Mol. Hum. Reprod. epub 31 May 2013

Monday, 17 June 2013

Monday Science: Gangnam Style vs Neuroscience

In our office there is a filing cupboard that cannot be opened. Once, a long time ago, it was closed and locked, and the key has long since disappeared. Nobody knows who closed it. Nobody knows who has the key. But somewhere this key does exist.

In kitchen drawers across the world, there are loose keys, whose keyhole has been lost to human knowledge. Sometimes we try an unknown key in an unopened lock, wiggling it around in the vain hope of finding a match, but ultimately we usually find disappointment.

Our knowledge of biology can be just as mismatched. The ‘lock and key’ analogy is often used to describe biological concepts to describe two molecules that fit together to make something happen. The key molecule fits into the lock molecule, opening the biological door: to use scientific terms, the ligand fits into (or on to) the receptor protein, triggering downstream signalling — think of a free-floating molecule pushing a big red button on a cell, causing the cell to light up. The problem is, we’re aware of many keys and many locks, but all too often we can’t find a match. We call the unassigned receptors ‘orphan receptors’.

One such orphan receptor is called Ptp10D but, because that’s a boring name, I’m going to call it Psy, like the bloke who rides invisible horses. Now a group of scientists led by Professor Kai Zinn at the California Institute of Technology, have worked out what the key is to getting Psy excited, leading to full-on, no holds barred nervous system development.

Zinn's team took as many unknown keys as they could, and tried them in the Psy lock. To do this in biology, specifically at the microscopic level of cell biology, you need to use a few tricks and tools. Enter my good friend the fruit fly, in which a genetic tool called the Gal4/UAS system has been introduced. Don’t worry about the jargon, all you need to know is that it allows you to increase the amount of a protein (in this case the potential keys) in very specific settings. When they increased the amount of one key, which is called Sas, they found that an enzyme-linked form of Psy started to glow, the very signal they were looking for that suggested an interaction.

Monday, 10 June 2013

Monday Science: The Animal Pairs Game

THIS is an activity I made for ThinkTank museum as part of a Meet the Scientist event on the theme of evolution and adaptation. Though my work does have a strong evolutionary angle, I do not specifically work on adaptation or taxonomy, but I wanted to gain experience demonstrating different topics. The activity – a pairs game – required a lot of effort on my part on the day, as I needed to explain constantly facts and concepts in biology (my audience were a mixture of ages, mostly young children); this I did not mind, and it was very rewarding for both myself and my visitor, but is worth warning about should you wish to try a similar activity.

The idea is to match animals based on similarity. That is, can you find two mammals? Two birds? There are traps and there are difficult animals, but the activity can be tailored depending on your audience (instead of two mammals, why not try pairing adaptations, habitats or common features such as spikes), and not all cards need to be used at any one time. I do urge you to read up on the subject of classification – it’s no longer really taught but it underpins so much of what we as biologists do. If we do not know what we are really looking at, and where it fits in the tree of life, how can we truly know the context of our results?

The full cards are below.