Like an “X” Machine

What makes a man, a man? It’s a question considered not only by philosophers and cultural theorists but also beer commercials and Chuck Norris fans. A breakthrough chromosome study published in March 3’s issue of Nature reveals an important new piece to the puzzle.

Refresher: Chromosomes are DNA bundles that carry genetic information, shaping microscopic blobs into complex, sophisticated organisms (and, sadly, cast members of Jersey Shore). The root biological difference between men and women is determined by sex chromosomes: Women have two “X” chromosomes in each of their cells, whereas men have one “X” and one “Y.”

A team of researchers, led by Erica Larschan of Brown University, focussed on why the single X chromosome in a male cell nucleus manages the vast majority of the genetic heavy lifting that requires two X chromosomes in female cells. The results are… scientific, potentially soporific if you are not the type who regularly chooses biology abstracts over this week’s Economist.

Basically, Larschan’s team proved a long-standing theory, that the X’s double-duty capability is enabled by a protein complex called “Male-specific lethal” or MSL. (We will forgo a second Chuck Norris reference, however tempting.) A series of tests conducted on fruit fly chromosomes—which also split the sexes in XX/XY style—demonstrated exactly how MSL increases, or “upregulates,” the male X chromosome’s gene expression.

Indisputably important, Larschan’s work is primarily of interest to other geneticists. Still, the man-about-town can learn from her discovery.

SCIENCE LESSON • The researchers used the same basic method one uses troubleshooting a software problem,
or figuring out which fuse is blown in an electrical panel. They suspected that MSL increased the genetic expression on the X chromosome; to see if that was true, they interfered with the MSL. Without the action of that protein complex, the X chromosome performed like any other chromosome, i.e. there was no extra productivity. Therefore, MSL caused the upregulation.

LIFE LESSON • Guys are so tough,
even something called “Male-specific lethal” only makes us stronger.

SCIENCE LESSON • Larschan’s team used one particular line of male fruit fly cells
that had already been heavily studied for MSL function. They were able to do their work because of many previous small observations and discoveries about fruit fly genetics. Instead of standing on the shoulders of giants, scientists often stand at the top of a very tall human pyramid of many other scientists, most of them of average height.

LIFE LESSON • As our over-active X chromosome proves,
even at the sub-cellular level, men enjoy the challenge of doing twice the work with half the resources.

SCIENCE LESSON • While the Y chromosome is what makes us men (it triggers testis development),
the X chromosome is what makes us fully functional men.

LIFE LESSON • While “X-chromosome upregulator” is a valid synonym for “male,”
it’s no replacement for chapbuddude or homey. Science can’t solve everything.

Image courtesy of ALiCe.

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4 thoughts on “Like an “X” Machine

  1. Hate to burst your bubble, but it only works this way in fruit flies. In humans, the extra female X chromosome is silenced, meaning that the male X chromosome does exactly as much ‘work’ as the female’s. Entertaining take on the research, though.

  2. Certainly helps explain why males over-compensate their entire lives! Hardly any wonder that female scientists were the ones to recognize this. Nice job, one and all!

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