By Michael Burel
Every graduate student has a contingency plan. You know, that thing you’d do if you were suddenly expelled from your program and no longer had semi-stale seminar pizza for sustenance. For me, that plan is to open a bakery. It’s a flawless idea. Everyone loves sweets (read: Everyone. Don’t let anyone fool you into thinking they don’t have a sweet tooth. They hide behind the thin ‘salty-food-is-better’ veil. Give them a cookie and see who is smiling now). And, as Ina Garten so famously chortled while sharing a recipe for irresistible chocolate chip cookies: “You can be miserable before you have a cookie and you can be miserable after you eat a cookie, but you can’t be miserable while you are eating a cookie.” Preach it, Ina.
But you know, sometimes a cookie just doesn’t cut it for graduate students. I mean, sure, on the outside we put on our big happy face (you know the one) and say through a forced grin, “Oh. Great. Seminar cookies…again. My favorite.” In reality, however, we do need actual food from time to time to exist on this planet. I’m talking about the kind of food that has vitamins (huh?), minerals (what are those?), fiber (like from a wicker basket?), and whole grains (isn’t that for cows?). In times of nutritional need, our bodies activate an intrinsic dowsing rod to hunt down food with the nutrients we desperately lack. That’s why patients with pica, a disorder characterized by an appetite for unusual things like sand and clay, often have a mineral deficiency: They seek these non-nutritive materials in a last-ditch attempt to restore, for example, a low iron count.
Now let me throw a wrench into the scheme: What if you couldn’t taste anything? How would your body know—in a time, let’s say, before we could scientifically determine the nutritional value of food—if something is good for you to eat? Indeed, animals that have lost the ability to taste still have preference for foods that are more nutritious and easier to digest (1, 2). But how?
In search for an answer, and for the second installment of Drosophila Diaries, scientists hunted for a gene in Drosophila that would abolish a fly’s ability to distinguish what is nutritionally beneficial from what is not. Monica Dus et al. led a study to really understand how animals blind to taste can still select the more nutritionally appropriate food choice, an ability that is potently augmented in times of starvation. At the core of their research was a genetic screen in otherwise normal, healthy flies to find a mutation that would prevent them from choosing a good sugar (the metabolically active D-glucose) from a bad sugar (the unusable L-glucose). They honed down on such a gene and named it—quite cutely—cupcake, which only seems appropriate: Put a cupcake and a bowl of bran flakes in front of a five-year-old and they will 99% of the time choose the cupcake. Nutritionally the best option? No. The more delicious, magical of the two? Absolutely.
The cupcake gene encodes a sodium/solute co-transporter whose mammalian ortholog works to move glucose across the small intestine into blood. Obviously, cupcake must be doing the same thing in flies: Without cupcake, flies can’t take up sugar into their hemolymph (bug blood) and therefore can’t sense the food’s nutritional value. A fly gives up all hope of even picking one sugar over another because, to the mutant, it’s all the same.
If only it were that simple.
You see, cupcake isn’t even expressed in fly guts. The group found that cupcake is expressed only in a very select group of neurons in the fly brain in a structure called the ellipsoid body. The ellipsoid body is part of a larger brain structure called the central complex, which modulates fly behavior and—quite intriguingly—processes the senses. By specifically putting cupcake back in these neurons, the authors rescued the ability of flies to sense which sugar was best for them. How cupcake works in these neurons to sense appropriate glucose still remains a mystery.
As graduate students, we often come face to face with difficult decisions: Should I attend this conference or get data for my upcoming committee meeting? Should I run this Western now or wait until Monday? And perhaps the most important of all: Should I pick the oatmeal raisin cookies or the random deli salad for seminar munchies? (Obviously the former). Too often, we subsist on foods that aren’t the best for us yet are readily available. I can’t help but wonder if it’s because we all have a little hypomorphic cupcake in us.
Which works for me, because my bakery business would be booming. Science wins again.
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