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Reality Check: How does the X-Men’s X-Gene create so many different mutants?

It can’t really do everything … or can it?

Since their debut in 1963, the X-Men have sworn to protect a world that hates and fears them, but here at AiPT! we’ve got nothing but love for Marvel’s mighty mutants! To celebrate the long-awaited return of Uncanny X-Men, AiPT! brings you UNCANNY X-MONTH: 30 days of original X-Men content. Hope you survive the experience…AiPT! Science is going all-in for Uncanny X-Month, with the most detailed look at X-Men biology anywhere, EVER. Today, Yelena Bernadskaya, developmental biologist specializing in genetics, returns to try to figure out how one little X-Gene can produce so many varied mutations.

A long time ago, some naughty Celestials came to Earth and threw a wrench into human evolution. They developed what is referred to as the X-Gene and inserted it into the genomes of humans’ hominid ancestors, where it sat quietly and eventually was passed down to modern humans. Then, in what amounts to something of a collective puberty, the X-Gene began to activate, giving its hosts mutant powers and abilities.

The activation of the X-Gene can be caused by traumatic events, but most often occurs around the time of actual, biological puberty. The question is, if individual mutants manage to live for so long prior to discovering their powers, how could the activation of one gene suddenly produce so many instantaneous changes? How far-fetched is this?

Wolverine and the X-Men #5, Marvel Comics

How it works, ordinarily

Taken at face value the X-Gene is just that, a gene. For the sake of this discussion we’re sticking to the standard scientific definition of what a gene is, a heritable unit of DNA that codes for a protein that has some kind of function.  A gene that is actively being used to produce a protein is said to be active and “expressing.”

Your genome (the entirety of your DNA) consists of a bunch of protein-coding genes that can either be activated or turned off. The trick to having a functional human is to deploy these genes strategically at the right time, in the right place. Runaway gene expression is a hallmark of disease states such as cancers. Nobody needs that.

Generally, people have two copies of each gene, one inherited from their father and one from their mother. These copies are often not identical — you can have one copy that codes for brown eyes and another that codes for blue eyes. The versions of genes you have for any particular trait are called your genotype. The way your genes actually manifest, i.e. whether you actually have blue or brown eyes, is called a phenotype. In the case of eye color, the dominant brown would trump the recessive blue and you’d have brown eyes.

Here’s the fun part — that eye example isn’t really true. While there are a small number of lone genes that control a single obvious phenotype, like those that produce a widow’s peak, that little protrusion of the hairline in the center of the forehead (two examples shown), most genes interact with a lot of other genes, resulting in many genes contributing to a single phenotype, and some single genes involved in multiple phenotypes.

Many geneticists actually like to think of genes as being organized into interconnected networks or circuits, where pulling one string can reverberate to create complex, systemic effects. The networks, although generally connected to each other, also have their own specific functions.

There’s a network for making eyes, another for making liver, another for placing a leg. Sitting at the apex of these complicated and tangled gene networks are a type of master regulator proteins called “transcription factors.” They act as switches and can turn on (or shut off) entire gene networks, producing large changes in body plan.

Because of these highly connected networks, making physical structures is a coordinated process of string-pulling and switch-flipping. When this happens in an embryo, it leads to the patterning and formation of basic body plans, like where you put the head and where you put the butt.

(A lot of this information came from studying the development of fruit fly larva, when intrepid scientists found they can make larvae with two butts, by shutting down the genes that specify the head, and thereby all the associated gene networks needed to make head structures. Naturally, these flies didn’t survive.)

Even more interestingly, scientists found that some appendages can be transformed into other appendages by tugging on single developmental genes, like putting feet where the antennae should be.  This is caused by a mutation in a single gene aptly called “antennapedia” (literally “antenna-feet;” fly scientists are the best at coming up with gene names).

X-traordinary X-pression

But these transformations happen early in development, not when the animal is an adult. Can we develop whole new organs or appendages later in life? The answer is “kind of,” but we’re really bad at it and have no way of controlling it.

There’s a category of benign tumors, called “teratomas” (literally “monster tumors”), in which the cells go haywire and start making random tissues and body parts. These tumors are often filled with hair and calcium deposits that look very much like teeth, and most often develop in ovaries. They can be completely asymptomatic or they might cause severe pain. In very rare cases these tumors can develop rudimentary limbs. So at most right now, we can kind of make a hairy pancake with some teeth.

What about extra eyes??? Image credit: Marvel Comics

Where does all this leave the X-Gene? If we think of it as a special type of transcription factor, we can imagine that when a mutation manifests, it turns on a great number of gene networks that remodel the body and generate new structures. We can also speculate about the existence of a mutant regulatory network that’s activated when expression of the X-Gene is forced, through either a traumatic or a biological event.

Even more interestingly, it could provide insight into why mutants have such varied powers. Maybe type of power depends on where the X-Gene first becomes expressed. If expressed in stem cells required for repair, it could produce healing abilities like Wolverine’s; expressed in the brain, maybe it could produce telepathic and telekinetic abilities like Jean Grey’s.

The real world understanding of genetic switches continues to evolve (pun intended!), we just need to find the right combinations for the right kind of powers.


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