PZ Myers posted Entry 744 on January 14, 2005 04:44 PM.
Trackback URL: http://www.pandasthumb.org/cgi-bin/mt/mt-tb.fcgi/742

Wnt signaling

The Wnt genes produce signalling proteins that play important roles in early development, regulating cell proliferation, differentiation and migration. It's hugely important, used in everything from early axis specification in the embryo to fine-tuning axon pathfinding in the nervous system. The way they work is that the Wnt proteins are secreted by cells, and they then bind to receptors on other cells (one receptor is named Frizzled, and others are LRP-5 and 6), which then, by a chain of cytoplasmic signalling events, removes β-catenin from a degradation pathway and promotes its import into the nucleus, where it can modify patterns of gene expression. This cascade can also interact with the cytoskeleton and trigger changes in cell migration and cell adhesion. The diagram below illustrates the molecular aspects of its function.

Wnt signaling

This is greatly simplified, of course. There are different pathways and different roles in different cells under different conditions. Mammals have 19 Wnt genes, so far, and as I mentioned above, have diverse functions. The obvious questions are where all this complexity originated, and what role the original Wnt gene played. One way to answer this question is to examine simpler organisms that separated from our messily complicated lineage long, long ago, and by comparison, try to infer what Wnt genes were present in our last common ancestor. Kusserow et al. (2005) have done this in a sea anemone, Nematostella vectensis, and got a somewhat surprising answer: our last common ancestor with a diploblast also had an elaborate array of Wnt genes.

Continue reading "A complex regulatory network in a diploblast" (on Pharyngula)

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Comment #13950

Posted by DaveScot on January 16, 2005 8:01 AM (e)

Surprising to whom?

In both the title and the conclusion, the authors emphasize the surprising complexity of our ancient ancestors.

Gee, it’s almost like all the biochemical complexity of life was there right at the LUCA billions of years ago and all the intervening time has just been rearranging the deck chairs.

Heck, that would even explain why single-celled organisms were the most widespread form of life from the word “GO” billions of years ago right on through to today.

I seem to recall a biochemist saying something like that 10 years ago. What was his name… oh yeah… I remember… some cat named Behe. I understand he’s something of a pariah amongst his peers for postulating such heresy.

Funny, the most natural thing in the world is for organized systems to become less organized over time. It’s called the second law of thermodynamics. Dr. Behe’s theory follows this law. And by the way, for you anti-sticker apologists, a law is more of a fact than a theory. You’d think materialists would be more open to Behe’s theory since it doesn’t violate the laws of nature, unlike some other theories. Go figure.

Comment #13959

Posted by Jeremy Mohn on January 16, 2005 10:54 AM (e)

DaveScot wrote:

Gee, it’s almost like all the biochemical complexity of life was there right at the LUCA billions of years ago and all the intervening time has just been rearranging the deck chairs.

How does this research suggest that the “biochemical complexity of life was there right at the LUCA billions of years ago?” Surely DaveScot knows what “diploblast” means. Diploblasts are much more complex than anything that existed “billions of years ago.”

Funny, the most natural thing in the world is for organized systems to become less organized over time. It’s called the second law of thermodynamics.

This does not apply to life on earth as long as the sun is shining. Does DaveScot really think the second law of thermodynamics has something to do with evolution?

And by the way, for you anti-sticker apologists, a law is more of a fact than a theory.

The word “fact” in science can be used interchangeably with the word “observation.” So DaveScot has really just pointed out that a law is more of an *observation* than a theory. To quote Jack Krebs from another thread:

Jack Krebs wrote:

Science starts with facts, and then builds tested hypotheses, derives laws, and eventually and ultimately constructs theories which tie together and help explain how all the facts are related to each other.

In other words, the progression of scientific knowledge starts with facts and ends with theories. This is not the impression one gets from statements like DaveScot’s.

Comment #13972

Posted by DaveScot on January 16, 2005 2:01 PM (e)

Jeremy,

Sorry, please accept my apology. It isn’t really science to talk about the genomes of ancient creatures as there’s no way to falsify any theories about them - DNA unfortunately doesn’t fossilize. I was pretending it was science instead of speculative history based on the sage advice “when in Rome, do as the Romans do”.

At any rate, it did seem reasonable to believe, granted it’s speculative history not science, that sea anemone and human lineages separated a long time ago. Does Cambrian period sound like a good guess for that? Sorry if I made the extrapolation from half a billion years to billions of years. I thought extrapolations like that were allowed in the realm of evolutionary conjecture.

The article in question was just one more bit suggesting that genomes of ancient creatures were more complex than had been previously guessed. If you want something that goes back even further - I’ve read that genes for various flavors of hemoglobin are found today in plants, animals, and fungi suggesting an ancestral hemoglobin gene in the last common ancestor betwixt all three phyla. Is the consensus guess that plants, animals, and fungi diverged from a common ancestor over a billion years ago?

Another interesting bit of trivia is that evidence of retrovirus infections have been found in plant genomes. It had been believed earlier that retrovirus infections were unique to vertebrates. Since retroviruses can shuffle genes between disparate species and since retroviruses can mutate at an extraordinary rate being based on much more volatile RNA instead of DNA this points to an array of possibilities for horizontal interspecies gene flow in the past offering alternative explanations for any number of things previously assumed to be evidence of hereditary gene flow. I couldn’t find a whole lot of research on it. It might be a target rich environment for future research grants.

Comment #13973

Posted by Wedgie World on January 16, 2005 2:12 PM (e)

DaveScott wrote:

Sorry, please accept my apology. It isn’t really science to talk about the genomes of ancient creatures as there’s no way to falsify any theories about them - DNA unfortunately doesn’t fossilize.

Of course there are ways of falsifying theories about them but that does require one to understand biology. SO far you have done little to support such a conclusion.
That genomes of ancient creatures were more complex than expected may help understand the Cambrian explosion.

Jeremy’s observations seem quite accurate.

Comment #13992

Posted by Jeremy Mohn on January 16, 2005 7:47 PM (e)

DaveScot-

Your frequent use of the phrases “speculative history” and “evolutionary conjecture” in reference to evolutionary research seem rather ironic given that your fellow ID promoters haven’t presented a single testable hypotheses concerning how organisms came to be the way we observe them today. Maybe you need a new irony meter.

And what about Behe’s “theory” to which you referred? Here’s the original proposal, as found in Darwin’s Black Box (1996):

“Suppose that nearly four billion years ago the designer made the first cell, already containing all of the irreducibly complex biochemical systems discussed here and many others. (One can postulate that the designs for systems that were to be used later, such as blood clotting, were present but not “turned on.” In present-day organisms plenty of genes are turned off for a while, sometimes for generations, to be turned on at a later time.) Additionally, suppose the designer placed into the cell some other systems for which we cannot adduce enough evidence to conclude design. The cell containing the designed systems then was left on autopilot to reproduce, mutate, eat and be eaten, bump against rocks, and suffer all the vagaries of life on earth.”

(pages 227-228)

I don’t know about you, but Behe’s “theory” sure seems like “speculative history” and “evolutionary conjecture” to me. Behe himself prefaced the above description by calling it a “speculative scenario.” Maybe before you criticize evolutionary research by calling it “speculative” you should closely examine the ideas you promote. At least the research described in PZ’s post is based on actual scientific evidence. Where is the evidence in support of Behe’s “theory?”

IIRC, Behe’s comments since 1996 suggest that he doesn’t take his own idea very seriously. Perhaps that’s because it wasn’t very well thought out. Mutations in the DNA for these “front loaded” genes would accumulate at an incredible rate since they would not be initially expressed and natural selection could not weed out the mistakes. These mutations would almost certainly render the genes inoperative before the time when they were to be “turned on.” Behe’s “speculation” is really just “careless guesswork.”