Hox complexity

Here’s a prediction for you: the image below is going to appear in a lot of textbooks in the near future.

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(click for larger image)
Confocal image of septuple in situ hybridization exhibiting the spatial expression of Hox gene transcripts in a developing Drosophila embryo. Stage 11 germband extended embryo (anterior to the left) is stained for labial (lab), Deformed (Dfd), Sex combs reduced (Scr), Antennapedia (Antp), Ultrabithorax (Ubx), abdominal-A (abd-A), Abdominal-B (Abd-B). Their orthologous relationships to vertebrate Hox homology groups are indicated below each gene.

That’s a technical tour-de-force: it’s a confocal image of a Drosophila embryo, stained with 7 fluorescent probes against different Hox genes. You can clearly see how they are laid out in order from the head end (at the left) to the tail end (which extends to the right, and then jackknifes over the top). Canonically, that order of expression along the body axis corresponds to the order of the genes in a cluster on the DNA, a property called colinearity. I’ve recently described work that shows that, in some organisms, colinearity breaks down. That colinearity seems to be a consequence of a primitive pattern of regulation that coupled the timing of development to the spatial arrangements of the tissues, and many organisms have evolved more sophisticated control of these patterning genes, making the old regulators obsolete…and allowing the clusters to break up without extreme consequences to the animal. A new review in Science by Lemons and McGinnis that surveys Hox gene clusters in different lineages shows that the control of the Hox genes is much, much more complicated than previously thought.

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How would ID have contributed?

Carl Zimmer brings up another essential point about the HAR1F study: it was work that was guided by evolutionary theory. The sequence would not have been recognized in the billions of nucleotides in the genome if it hadn’t been for an analysis directed by the principles of evolution.

Wells’ diatribe was amazingly wrong. I looked at it again and there could be another half-dozen essays in just picking up apart the stupidity in it.

Wells: “Darwinism is Doomed” because we keep making progress

There are days when I simply cannot believe how dishonest the scoundrels at the Discovery Institute can be. This is one of them. I just read an essay by Jonathan Wells that is an appalling piece of anti-scientific propaganda, an extremely squirrely twisting of some science news. It’s called “Why Darwinism is doomed”, and trust me, if you read it, your opinion of Wells will drop another notch. And here you thought it was already in the gutter!

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Squid Hox genes

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It’s April (not anymore—it’s September as I repost this), it’s Minnesota, and it’s snowing here (not yet, but soon enough). On days like this (who am I fooling? Every day!), my thoughts turn to spicy, garlicky delicacies and warm, sunny days on a lovely tropical reef—it’s a squiddy day, in other words, and I’ve got a double-dose of squidblogging on this Friday afternoon, with one article on the vampire squid, Vampyroteuthis infernalis, and this one, on squid evolution and cephalopod Hox genes.

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Evolution of alcohol synthesis

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We need to appreciate beer more. Alcohol has a long history in human affairs, and has been important in purifying and preserving food and drink, and in making our parties livelier. We owe it all to a tiny little microorganism, Saccharomyces cerevisiae, which converts complex plant sugars into smaller, simpler, more socially potent molecules of ethanol. This is a remarkable process that seems to be entirely to our benefit (it has even been argued that beer is proof of the existence of God*), but recent research has shown that the little buggers do it all entirely for their own selfish reasons, and they’ve been busily making alcohol that has gone undrunk by humankind for tens of millions of years.

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Cats, candy, and evolution

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Here’s a small taste of Roald Dahl’s Charlie and the Chocolate Factory, a sweet story about a poor boy and his visit to an amazing candy factory…you’ve probably heard of it, since the new movie is getting a lot of press.

Only once a year, on his birthday, did Charlie Bucket ever get to taste a bit of chocolate. The whole family saved up their money for that special occasion, and when the great day arrived, Charlie was always presented with one small chocolate bar to eat all by himself. And each time he received it, on those marvelous birthday mornings, he would place it carefully in a small wooden box that he owned, and treasure it as though it were a bar of solid gold; and for the next few days, he would allow himself only to look at it, but never to touch it. Then at last, when he could stand it no longer, he would peel back a tiny bit of the paper wrapping at one corner to expose a tiny bit of chocolate, and then he would take a tiny nibble—just enough to allow the lovely sweet taste to spread out slowly over his tongue. The next day, he would take another tiny nibble, and so on, and so on. And in this way, Charlie would make his ten-cent bar of birthday chocolate last him for more than a month.i-a420ae8c62e074dde7e2fce0652d306e-tinystop.gif

That’s how it is published, at any rate. What if it read something like this?

Only once a year, on his birthday, did Charlie Bucket ever get to taste a bit of chocolate. The whole family saved up their money for that special occasion, and when the great day arrived, Charlie was always presented with one small chocolate bar to eat all by himself. And each time he received it, on those marvelg ynfg, jura ur pbhyq fgnaq vg ab ybatri-a420ae8c62e074dde7e2fce0652d306e-tinystop.gif, ur jbhyq i-a420ae8c62e074dde7e2fce0652d306e-tinystop.gifrry onpx n gval ovg bs gur cncre jenccvat ng bar pbeare gb rkcbfr n gval ovg bs pubpbyngr, naq gura ur jbhyq gnxr n gval avooyr-whfg rabhtu gb nyybj gur ybiryl fjrrg gnfgr gb fcernq bhg fybjyl bire uvf gbathr. Gi-a420ae8c62e074dde7e2fce0652d306e-tinystop.gifr arkg qnl, ur i-a420ae8c62e074dde7e2fce0652d306e-tinystop.gifbhyq gnxr nabgure gval avooyr, naq fb ba, naq fb ba. Naq va guvf jnl, Puneyvr ji-a420ae8c62e074dde7e2fce0652d306e-tinystop.gifhyq znxr uvf gra-prag one bs oveguqnl pubpbyngr ynfg uvz sbe zber guna n zbagu.

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Hox cluster disintegration

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Hox genes are metazoan pattern forming genes—genes that are universally associated with defining the identities of regions of the body. There are multiple Hox genes present, and one of their unusual properties is that they are clustered and expressed colinearly. That is, they are found in ordered groups on the chromosome, and that the gene on one end is typically turned on first and expressed at the head end of the embryo, the next gene in order is turned on slightly later and expressed further back, and so on in sequence. That the tidy sequential order on the chromosome is associated with an equally tidy spatial and temporal pattern of expression in the body has always been one of the more fascinating aspects of these genes, and they are one of the few cases where we see an echo of phenotypic form comprehensibly laid out in the DNA.

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Palaeos reborn!

First I reported that Palaeos was lost, and then that it might be found, but now it looks like we can safely say it is being reborn. The old version of Palaeos has been at least partially restored, but the really important news is that a Palaeos wiki has been set up and people are working on reassembling old content and creating new information in a much more flexible format. If you’ve got some phylogenetic or palaeontological expertise, you might want to consider joining the Palaeos team and helping out with this big project.

3.3 million years old, 3 years old

Say hello to Selam, or DIK-1-1, a new and very well preserved member of the family discovered in Dikika, Ethiopia. She belongs to the species Australopithicus afarensis and is being called Lucy’s little sister.

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She was only a toddler when she died about 3.3 million years ago, and from the teeth the authors estimate that she was about 3 years old. Most of the skeleton is intact, but doesn’t seem to have yet been fully extracted from the matrix.

Some of the surprises: the hyoid bone is chimpanzee-like, and implies chimp-like vocalization abilities. She had a long way to go before she could have a conversation. The fingers are long and curved, and the scapula is more gorilla-like than ours; there is a suggestion of better arboreal ability than we have.

Alemseged Z, Spoor F, Kimbel WH, Bobe R, Geraads D, Reed D, Wynn JG (2006) A juvenile early hominin skeleton from Dikika, Ethiopia. Nature 443:296-301.