Generic bumps and recycled genetic cascades

How do you make a limb? Vertebrate limbs are classic models in organogenesis, and we know a fair bit about the molecular events involved. Limbs are induced at particular boundaries of axial Hox gene expression, and the first recognizable sign of their formation is the appearance of a thickened epithelial bump, the apical ectodermal ridge (AER). The AER is a signaling center that produces, in particular, a set of growth factors such as Fgf4 and Fgf8 that trigger the growth of the underlying tissue, causing the growing limb to protrude. In addition, there’s another signaling center that forms on the posterior side of the growing limb, and which secretes Sonic Hedgehog and defines the polarity of the limb—this center is called the Zone of Polarizing Activity, or ZPA. The activity of these two centers together define two axes of the limb, the proximo-distal and the anterior-posterior. There are other genes involved, of course—this is no simple process—but that’s a very short overview of what’s involved in the early stages of making arms and legs.

Now, gentlemen, examine your torso below the neck. You can probably count five protuberances emerging from it; my description above accounts for four of them. What about that fifth one? (Not to leave the ladies out, of course—you’ve also got the same fifth bump, it’s just not quite as obvious, and it’s usually much more tidily tucked away.)

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More stem cell talk

DarkSyde is on the stem cell story, and he uses Neurotopia’s summary of the biology.

I just don’t understand the other side’s argument. Adult stem cells are not a substitute for embryonic stem cells, at least not yet. The anti-stem cell research crowd wants to claim that we don’t need ES cells, that AS cells will do everything we need, but they don’t think it through. If we want to make AS cells that are functionally equivalent to ES cells, we need to understand ES cells—but they want to deny us the ability to look at ES cells. Furthermore, if we could convert an AS cell line to totipotency what we’d have is…millions of cells we could replicate in the lab, each of which has the potential to become a human being. We’d go from a few “snowflakes” to a blizzard. Then what?

There are no limits to creationist stupidity

Every time I talk to creationists, I’m always stunned at the depth of their misconceptions. There are always the same old boring arguments that are ably dismissed with a paragraph from the Index to Creationist Claims, but there are also occasions when they get, errm, creative, and unfortunately they always take your gape-mouthed I-can’t-believe-you-are-so-stupid-that-you-said-that reaction as a triumphant vindication that they must be right.

Orac takes a right-wing idiot to task, and I don’t need to jump in—he’s done a fine job dismantling him—but I made the mistake of actually reading the ghastly blog article he’s criticizing, and even worse, reading some of the comments there. The very first comment will make your jaw drop at the combination of sublime arrogance and impenetrable stupidity. There’s a list of 7 objections to evolution, all wrong, but I’ll spare you and show just the first.

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A stem cell veto prediction

Despite Brownback’s snowflake stunt and Santorum’s insistence that zygotes are persons, the House stem cell bill, HR810, has passed, as have the two inconsequential smokescreen bills that Santorum tossed up. It’s going to be interesting to hear Bush’s stammered excuses when he vetos it; I’d figure he’d be reluctant to do the veto because it would mean taking undeniable responsibility for an action, something he doesn’t like to do, but then I realized he has another out. He’s going to blame God for telling him to kill the bill.

I predict that he will make some pious excuse like that when he vetoes it. That’s our George: he didn’t do it, it’s not his fault, the buck stops somewhere else, he’s a delegater, not a responsibility-taker.

Department of obviousness

Well. I don’t see the point of this study, but I suppose there are people who need to be clubbed about the head with the obvious who would be well-served by reading it. It’s a study to determine whether clones would have separate identities.

Umm, yeah?

They determined this by interviewing twins, who are clones of one another.

OK, yes?

From these findings the scientists said they could assume a clone would probably not feel their individuality was compromised by sharing genes with someone else; that their relationship with their co-clone was a blessing; and their uniqueness was not a negative thing.

That’s a relief. We can stop worrying about the clone armies full of self-loathing bodies with a single mind between them, I guess. I wonder if they also pursued the question of why, in any pair of twins, one individual gets all the good qualities, and the other is always pure evil?

Never mind. Try googling “soul” and “clone”—there are way too many people in the world who take that worry seriously. Maybe this was a necessary study after all.

David Prentice’s shoddy stem cell scholarship

A reader sent me copy of a letter that will be published in Science this week, criticizing the dishonest tactics of the anti-scientific adult stem cell “advocates” (in quotes because they aren’t really science advocates of any kind—they’re only using it as an issue to limit stem cell research.) Anyway, it raises the interesting question of who you’re going to believe: scientists with expertise in the issues under discussion, or a flunky for Sam Brownback and shill for the religious right?

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