It’s appropriate to have a poem about pregnancy today—so go read Adapted, Not Designed. It’s lovely, and I think you can tell from the title that there’s another reason I like it.
Jerome a Paris has a first-rate overview of wind power on Daily Kos. I’m in a windy part of the world where this form of energy has great potential, and there is much local enthusiasm for wind turbines. Our first one is up just north of town, where I can sometimes catch a peek of it from my neighborhood when the trees aren’t all covered with leaves and where we always see it as one of the landmarks as we’re driving into town. I think they’re beautiful. Coal plants may be less obtrusive when they can be kept distant, but I’d rather see a row of wind turbines on a ridge than a smokestack on the far horizon.
Crap. Coturnix tagged me with this beautiful bird meme, and I am the wrong person to ask. I don’t get out much, preferring to sit in the lab or the library, so my favorite birds are all in pieces and dead. But OK, since he asked…
Bird digits
Bird teeth
Bird brains
Jurassic bird brains
Bird lungs
Oviraptor pelves (does that count?)
Cretaceous bird embryos
Four-winged birds
Waimanu
And Archaeopteryx, of course.
Flitting about as I have lately means I’ve been missing this, that and the other thing. So here’s a quick summary.
Now I’ve got a couple of finals to give, and man, I’m exhausted. Driving to Madison and back again in one day is too much for this tired old guy—we got back about midnight last night, and then I had to drag myself out of bed at 6 to finish writing one of my exams. And then tonight…more grading.
Lots of people have sent me links to this—thanks, all!—and it’s the perfect thing to lift me out of the finals week blahs, and it’s also just in time for Mother’s Day on Sunday: The Devonian Blues.
Every single girl and every little boy
Was born from the clan of the wayward Dipnoi
Don’t let the preacher man spoil all the fun
Took a lot more than 6 days to get the job done
Amphibians, reptiles, birds, mammals and man
All belong to the fish tribe, doncha’ understand?Your momma was a lobefinned fish
My momma was a lobefinned fish
Sing along, everyone!
It’s another traveling day for me! I’m off to Minneapolis for a few meetings, and also this important event tonight:
Café Scientifique
Antibiotics in Agriculture
with Timna Wyckoff
Tuesday, May 9, 6-8 p.m.
Varsity Theater, Dinkytown
Free. Must be 18 or older to attend.The Union of Concerned Scientists estimates that more than 70% of the antibiotics produced each year in the U.S. are used in livestock production. How exactly are antibiotics used in agriculture? Do those uses lead to bacterial resistance? Does this have an impact on human health? Timna Wyckoff, assistant professor of biology at University of Minnesota Morris, will discuss the questions and answers surrounding this controversial topic, and share her recent work involving bacterial antibiotic resistance at conventional and organic dairies. Sponsored in part by the University of Minnesota Morris through their Café Scientifique program.
Note that the speaker is UMM’s very own Timna Wyckoff. Yay, us!
Then, tomorrow I have to scoot on down to Madison, pick up #2 Son and a few tons of accumulated college stuff, and zip all the way back to Morris. I’m hoping to have a few oddments of time to post a few things—there’s some new stuff on diploblast Hox genes that I want to mention, that will fit in well with the reruns I ran yesterday—and I’m also going to squeeze in some more grading. This is a fun week, isn’t it?
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.
One of the hallmark characters of animals is the presence of a specific cluster of genes that are responsible for staking out the spatial domains of the body plan along the longitudinal axis. These are the Hox genes; they are recognizable by virtue of the presence of a 60 amino acid long DNA binding region called the homeodomain, by similarities in sequence, by their role as regulatory genes expressed early in development, by the restriction of their expression to bands of tissue, by their clustering in the genome to a single location, and by the remarkable collinearity of their organization on the chromosome to their pattern of expression: the order of the gene’s position in the cluster is related to their region of expression along the length of the animal. That order has been retained in most animals (there are interesting exceptions), and has been conserved for about a billion years.
Think about that. While gene sequences have steadily changed, while chromosomes have been fractured and fused repeatedly, while differences accumulated to create forms as different as people and fruit flies and squid and sea urchins, while continents have ping-ponged about the globe and meteors have smashed into the earth and glaciers have advanced and retreated, these properties of this set of genes have remained constant. They are fundamental and crucial to basic elements of our body plan, so basic that we take them completely for granted. They determine that we can have different regions of our bodies with different organs and organization. Where did they come from and what forces constrain them to maintain their specific organization on the chromosome? Are there other genes that are comparably central to our organization?
There are quite a few genes that are known to be highly conserved in both sequence and function in animals. Among these are the various Hox genes, which are expressed in an ordered pattern along the length of the organism and which define positional information along the anterior-posterior axis; and another is decapentaplegic (dpp) which is one of several conserved genes that define the dorsal-ventral axis. Together, these sets of genes establish the front-back and top-bottom axes of the animal, which in turn establishes bilaterality—this specifically laid out three-dimensional organization is a hallmark of the lineage Bilateria, to which we and 99% of all the other modern animal species belong.
There are some animals that don’t belong to the Bilateria, though: members of the phylum Cnidaria, the jellyfish, hydra, sea anemones, and corals, which are typically radially symmetric. A few cnidarian species exhibit bilateral symmetry, though, and Finnerty et al. (2004) ask a simple question: have those few species secondarily reinvented a mechanism for generating bilateral symmetry (so that this would be an example of convergent evolution), or do they use homologous mechanisms, that is, the combination of Hox genes for A-P patterning and dpp for D-V patterning? The answer is that this is almost certainly an example of homology—the same genes are being used.
