Ah, the evils of strong drink. Or weak drink. You all know that you shouldn’t drink alcohol to excess during pregnancy, and the reason is that it can affect fetal development. We take zebrafish eggs and put them on a real bender: we soak them in various concentrations of alcohol (which are hard to compare with human blood alcohol levels, I’m afraid, but trust me: these are such gross levels of ethanol that mere humans would be dead and pickled. Fish are tough), and let them stew for hours. Since fish development is much, much faster than human development, it’s rather like having a woman start drinking straight Everclear a few weeks after discovering she’s pregnant, and staying snockered throughout the first trimester.
So don’t try this at home, kids.
The animal on the left is a teetotaler control. The one on the right is going to get washed in 3% alcohol at about 4 hours of development. It’ll be obvious; a label will pop up, and also the eggs are embedded in agar to immobilize them, and the agar will go cloudy and dark for a while as the alcohol soaks in.
Even if you aren’t intimately familiar with fish embryology, you should be able to see that the one on the right develops more slowly. Especially at the end, the one on the left will be twitching vigorously and spinning in the chorion, while the lush on the right is much slower. There are also some subtle deformities in tail shape, and you might notice odd schmutzy gunk on the animal’s epidermis…more about that later.
Also, you’ll notice that we started both recordings immediately after fertilization—I was hovering over the tank, and as soon as momma and daddy squirted out the gametes, I scooped them up and slapped ’em down in a dish, to guarantee that everything was starting precisely in synchrony. These movies start a little earlier and go on a little longer than the previous example.
By popular request, here’s a roughly annotated version of that zebrafish development movie.
Stuff to watch for:
This movie starts at the 8-16 cell stage. The cells of the embryo proper (blastomeres) are at the top, sitting on a large yolk cell.
The pulsing is caused by the synchronous early divisions of all the cells. They lose synchrony at the mid-blastula transition.
Epiboly is the process by which the cells migrate downward over the yolk. An arrow will briefly flash, pointing to about 11:00, in the direction of the animal pole (where the future nose will form, sorta). That happens just before the whole animal begins to rotate within the chorion, just to make following everything more difficult.
After the animal rolls over, the animal pole is pointing straight up at you, and the migrating cells will form the germ ring, a thickening around the equator of the embryo. Cells will also migrate towards one point along the ring, forming a thickening called the keel. This is where the embryonic axis is forming; cells are migrating into the interior at this point in the process called gastrulation, and this region is roughly equivalent to the dorsal lip of a frog.
The whole animal is going to roll over again, this time to its side. The keel is thickening and lengthening towards the animal pole. The body of the fish is going to form along the right side of spherical embryo in this view.
While the keel is extending anteriorly, cells are still also migrating to surround the yolk—epiboly continues, with the yolk bulging out a bit until it is finally surrounded and closed off at the blastopore.
The head and tail extend. You’ll see the eye forming, so you’ll be able to tell which end is the head end.
Along the right side, you’ll also see the tissue form regular little blocks: these are the somites, or body segments.
The tail continues to extend and lifts off the surface of the yolk. When there are about 18 somites (the resolution is too low, so don’t try to count them), the animal will begin to twitch.
I’ll load up another one in a bit that will show a hint of the horrible stuff we do to them in the lab: we get the babies drunk and watch deformities develop.
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.
Hey, this is a pretty good interview of Richard Dawkins by Jeremy Paxman. I don’t know much about this Paxman fellow, but he asks hard, sharp questions, yet still gives Dawkins plenty of time to answer them. That’s good interviewing technique, I think.
I’m not too impressed with the spartan set, putting them both in plain uncomfortable-looking chairs set all alone in an empty, echoing room…but it does put the focus on the words. They should have saved a few more pennies and just done audio.
(via Father Dan)
At my talk on Tuesday, the centerpiece was a short movie of zebrafish development—I was trying to show just how amazingly cool the process was. People seemed to like that part of the show, at least, so I thought I’d try to figure out this YouTube doohickey and upload it for general viewing. So here it is, a timelapse recording of about 18 hours of zebrafish embryology compressed into 48 seconds:
I’ve got more, and my students will be making videos of their own soon enough, so maybe I’ll try uploading some other stuff soon. I’m discovering that YouTube is a little tricky about the aspect ratio, and the conversions do add some distracting compression artifacts to the movie…I may have to tinker quite a bit to get a more satisfactory image.
We have a new 527 political organization specifically set up to fight for the representation of science and engineering in politics and policy. Michael Stebbins has the details, and you can read the scientists’ and engineers’ bill of rights here. If you’re interested, join now!
The odious Ken Mehlman has announced that that mob of pigs, scoundrels, and theocrats will be slouching into Minneapolis on September 1-4, 2008. Anyone else care to join me in the protest lines that week?
When we get tired of yelling obscenities and imprecations at the parasites, we can always duck into the Science Museum of Minnesota, just down the street, for revitalization. Or we could just hang out in the SMM the whole time and take visiting Rethuglicans on tours of the dinosaur exhibit, and watch them stroke out and gasp for breath.
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!