Monday, 25 July 2011

Dude looks like a Lady

If anyone can tell us how far we’ve come from Victorian views of sexuality, it’s the makers of women’s undergarments. As we’ve shed our voluminous petticoats and embraced the “man bag,” we’ve also started to accept that human sexuality has a few more shades of gray than may have been acknowledged in days of yore. While it’s not much of a stretch to use clothing to blur gender boundaries, you might be surprised to learn just how delicate your physical gender can be. When it comes to gonads, it really can be the cut of your genes that matters.
            And now for the basic biology version of the hated “birds and the bees” discussion: Mom provides the egg (one set of genes), and Dad provides sperm (a second set of genes). When the two meet up, under circumstances best described by parents the world over, they fuse and the two sets of genes form the necessary DNA to make a whole little person. The genes in question are in bundles called chromosomes (23 pairs in human cells), and the sex of the bouncing baby is determined by whether they carry the X or Y flavour of the sex chromosome. As all women have two X chromosomes and men have one X and one Y, the sex of the baby is dependant on whether the lucky egg-meeting sperm is of the X or Y persuasion. So the gender of the baby is determined, forever and always, by the sperm that wins the race, right? Normally, yes, but biology also has some tricks up its sleeve.
            The reason that the X and Y chromosomes are so all-important in gender decisions, beyond their nifty alphabetical designations, is the genes they carry. Some of these encode for proteins that produce sex hormones. Hormones are small molecules in your body, and the ones from the ovaries and testes are responsible for all the differences between male and female bodies. Incredibly, every function, feature, and fashion sense that defines our genders boils down to the initial decision for a single cell type to become either Sertoli cells (which are part of the testicle) or ovarian granulosa cells. These cells later play a key role in production of gender-appropriate hormones, resulting in development of everything from genitalia in the womb to scruffy adolescent mustaches.
            If the difference between developing Sertoli cells and granulosa cells is the rather important one of gender, surely this process occurs early and is promply cast in stone, right? Actually, like so many things in our body, the cellular decision to develop into one cell type or the other is controlled by a balance of inputs from two opposing “male” and “female” signaling pathways. Even more surprisingly, regardless of the identity of that initial sperm, if key components of one pathway are disrupted, the opposite gender will win out. That is to say that even if someone is genetically male (XY), if there is something wrong with this signaling pathway from the Y chromosome, they will develop like a female, and vise versa. If that gender jack-in-the-box doesn’t knock your unisex socks off, consider that new research indicates this can happen at any point in life. A recent paper describes how disrupting the “male” pathway in adult mouse testes resulted in these organs actually turning into ovaries.
            These experiments don’t offer practical applications, nor is this at all likely to happen spontaneously (don’t worry guys, you can stop clutching your pants in terror). They do, however, give us fascinating insight into what our genders really are and where they come from. Boy meets Girl, and Sperm meets Egg, but the new life emerging from those unions always looks just like its real Dad: biochemistry.

Monday, 18 July 2011

Glowing Green Mushrooms Seem Pretty Magical to Me…

            If you ask me (or any mycologist) the term “magic mushrooms” isn’t nearly specific enough to describe the psychedelic variety usually implied. The truth of the matter is that lots of mushrooms are pretty darn magical. Aside from providing a tasty side dish, these fabulous fungi produce an astounding array of chemical compounds with powerful effects. From delectable truffles, to potent poisons, many mushrooms have a profound ability to spice up an otherwise bland afternoon. One of the most amazing fungal feats, however, is best appreciated not by eating, but by looking. That green glow isn’t in your head, it’s the forest night-light: fungal bioluminescence!
            Before delving into their Lite-Bright-like capabilities, we should answer the question: what exactly is a mushroom? When it comes to the world of fungi, our umbrella-shaped friends are literally just the tip of the iceberg. The mushrooms we see growing above ground (and appearing on our dinner plates) are only one part of a larger fungal organism. The Fungi are a very diverse group of organisms and have many shapes and forms. Most fungi, however, grow in an inter-connected mesh of microscopic tubes called mycelium. The cells that make up the mycelium are called hyphae. Somewhat similar to slime-mold plasmodium, hyphae are cells with multiple nuclei; and somewhat similar to filamentous algae, they grow in long strands about 20 times finer than human hair. They grow progressively longer at their tips, and branches form on existing hyphae to form complicated networks. Some mycelium networks can only be described as huge. In fact, a single fungus has been identified that is estimated to cover 900 ha and be about 9000 years old.
            Although fond of edible fungi, I can’t say I’ve ever ordered a Monterey jack and mycelium burger, so where do mushrooms come into this hyphae-delic picture? As I mentioned, mushrooms are a part of the larger fungal organism, specifically the spore-spreading part. Mushrooms are called fruiting bodies and grow above the ground to spread the spores of the underground mycelium. You can think of the fungus as a specialized structure or “organ” of the fungus that has a specific job to do: spread the genetic material of the fungus to a wider area than the mycelium is likely to grow.
Because they grow above ground, mushrooms are also “the face” that the fungus presents to the world. Like any good spokesperson, some mushrooms have an enlightening way of advertising: they glow. The neon green glow, reminiscent of glow-in-the-dark rubber toys, is a result of some very interesting biochemistry called bioluminescence. Bioluminescence literally means light from life, and it is produced by all kinds of life forms, including plants, animals, bacteria, and fungi. The two main players are luciferin (the general name for the group of pigments that are used in bioluminescence), and luciferase (the enzyme helping the reaction along). Like many things that seem pretty magical in biology, bioluminescence is all about chemistry: the luciferase combines luciferin and oxygen to make a high-energy molecule. Like Calvin after one too many bowls of Chocolate Frosted Sugar Bombs, this high-energy molecule is not very stable. It undergoes a second chemical reaction to form a lower-energy molecule, releasing the excess energy as light.
Although not the tastiest of mushrooms (and frequently rather poisonous) bioluminescent fungi have fascinated night-time forest-wanderers for centuries. Their light has been used to mark a luminous path in the woods, and even to illuminate the cabin of the early Turtle submarine. A campfire may make a good s’more, but with Nature’s amazing chemistry there is more than one way to light up the night.

Thursday, 7 July 2011

Did Dinosaurs use Celsius or Fahrenheit?

Photo Credit

As humans there are three ways we’re used to having our temperature taken: under the tongue, in our ears, and the “other” way. Regardless of our personal preferences, we can probably all agree that it is pretty darn difficult to apply any of these techniques to a dinosaur. So barring time machine development, how do we measure the body temperature of our pre-historic pals? Surprisingly, the trick is in the teeth. From molars to metabolism scientists are using some pretty “cool” chemistry to dig up answers.
To start out, let’s talk about metabolism, baby. Our metabolic rate is how fast we break down food, build up body mass, and generate heat. In general, a high metabolic rate means a higher general activity level and higher body temperature. Animals considered to be “warm blooded” have a high metabolic rate and generate their own heat internally, while “cold blooded” animals have a low metabolic rate and get much of their heat from the environment (picture a lizard sunning itself on a rock). This doesn’t mean, however, that “cold blooded” animals always have a lower body temperature, but that their temperatures fluctuate with their environment. In fact, their peak temperatures can be even higher than their “warm blooded” cousins. For this reason, these terms have been replaced by “endotherms” that generate temperature internally, and “ectotherms” that have their body temperature highly dependent on factors outside the body.
Our understanding of dinosaur body temperature has undergone a pretty major makeover over the last two decades. The image of dinosaurs as cold-blooded overgrown lumbering lizards has morphed into a portrait of a much more active and agile group of animals. This increased athletic prowess implies an increased metabolic rate, and sparked the idea that dinosaurs may have been endothermic. Being the investigative creatures that they are, scientists set out to study dinosaur metabolism and body temperature by measuring bone growth patterns, modeling behavior, and studying clues about athletic performance found in footprints. Although many of these studies pointed to an endothermic lifestyle, no real agreement on body temperature was reached.
That was until a group of researchers used the chemistry of dino tooth enamel as a trans-millennial thermometer to accurately measure the average body temperatures of some pre-historic behemoths. Wait just a second, temperature from tooth enamel? How can that work? The answer lies in the power of isotope chemistry. To understand this we have to go down the level of individual atoms of the elements carbon and oxygen. While most atoms of carbon have 12 particles in their nuclei and most oxygen atoms have 16, a very small percentage have extra neutrons and make carbon atoms with 13 particles and oxygen atoms with 18 particles. At high temperatures these “heavy atoms” act pretty much the same as all the other atoms, but at low temperatures they are more likely to bond to each other than one of the lighter atoms. You can think of this like a bad cocktail party: if everyone is really low energy you’re more likely to stick with your friends, but if the party really gets going you're going to meet and mingle with more people. In a technique called “clumped isotope thermometry” scientists measure the proportion of heavy carbon and oxygen that bonded together during tooth formation, effectively measuring the energy level of the tooth-growing party, or dinosaur body temperature.
From analyzing several teeth from large Jurassic Sauropods (“long-necks” to those who remember “The Land Before Time”) researchers calculated their body temperature to be between 36 and 38 oC. This is around the same range as most modern mammals. It’s not as simple as whipping out the thermometer from the medicine cabinet, but an inspiring example of how our basic scientific understanding of the world around us can enable scientists to solve seemingly impossible problems. Today dinosaur temperatures, tomorrow, conversations with Neanderthals? Don’t be too quick to rule it out…