What in the FruitFly is a “Hox Gene?”

Have you ever had an interior designer???

Maybe you don’t know it, but you’ve had more than one: Hox Genes. Just like the guys with great hair and perfect taste in wine, hox genes are one of many mechanisms responsible for the way you get mapped out while mom is pregnant with you.

Let’s start at the beginning… the PG13 version. So mom and dad flirt… FASTFORWARD… you’re now a zygote. Welcome to the world. You’ve got nine months of preparation before you can come out to play, so there’s not a moment to waste. You’ve got a few million cells to produce… time for crazy amounts of mitosis!!

But wait… mitosis produces identical cells. Right? And if all the cells are the same, then you end up with a blob and not a baby… right?

Yup! So there has to be something done to make the cells different. Almost immediately after the signals are sent through the cell that say “HEY! We’ve been fertilized!”, the genes are expressed that say “LISTEN LISTEN LISTEN!! We need to set some stuff straight. I don’t want to have to explain this to you stupid cells again. Over here is going to be the top and over there is going to be the bottom. Over there is going to be left, and right is going to be on that side. Front is going to be over here and back is going to be over there. GOT IT?!”

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Okokok, so proteins don’t actually talk. But essentially, that’s what the first regulatory genes do – make every spot in the fetus different somehow. They set up the “chemical environment” of the cells, and the other genes that make a baby obey the gradients of…. you know what? I’m getting tongue tied here, so I know you probably don’t know what’s going on.

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Genes are dumb little ugly gremlins that do only what they’re told and nothing more. They all already know their instructions: When your room is painted blue and someone upgrades your cable to digital, make this protein… Don’t ask questions, just do it.
Obviously, all the genes can’t be given those same conditions, or else we’d have the same problem: all the genes would be making all proteins at the same time… BLOB BABY. So, many genes have different conditions, but not all (sometimes it’s better to have more than one gene respond to the same conditions… i’ll write a post on that later).

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NOW, coming full circle! Hox genes are some of the first genes (for all intensive purposes) that are expressed during development. The main purpose of the proteins that they make are to SERVE AS THE CONDITIONS THAT TELL OTHER GENES WHEN TO BE EXPRESSED. So, visualize a cell at the tail end of a puppy fetus. Remember those genes that are expressed to make every spot different? The one of the hox genes in that tail cell has been instructed to express that hox protein when it’s in that spot in the tail.

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NOW, let’s move on from here… delving a bit deeper. The proteins that hox genes produce are called transcription factors. They are responsible for turning on other genes. Remember how I said earlier that some genes are expressed at the same time? Hox genes do that. That hox gene in the puppy tail is going to turn on all the genes that make tools to make tail (versus genes for the tools to make nose or paw).

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That’s all. Hox genes simply provide the tools to make certain body parts. They’re a little more complex than other genes, though, in that once a hox gene is expressed in an area, that area takes on an identity that it can never shed. If a cell is in the area of the fetus where hox genes for arm are being expressed, that cell CAN’T BE ANYTHING BUT ARM.

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UPDATE: I’ve received some feedback from readers stating that this concept still isn’t quite clear. I’ve created a forum topic to bounce ideas and explanations. If you still need help grasping this one, click here to  head on over and check it out!

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Oh, yeah. I almost forgot. YAY! NO MORE BLOB BABY!!!