This is a short video clip of myotome formation in a zebrafish embryo — it’s the subject of an upcoming column in Seed, so I’m putting a short visual aid here.
You can Download the Quicktime movie (620K), or you can watch it via YouTube. Watch closely, it’s short and it flies by!
If you’re totally mystified still, let me orient you. Here’s a whole zebrafish embryo. There’s a large yolk filling most of the center of the image, and the embryo itself arcs along the dorsal side, stretching from where I’ve labeled the eye to the tailbud.
Along the length of the trunk, you might be able to see some periodic seams, a few of which I’ve marked with black arrows. These are the muscle segments or somites. They start forming in the trunk, and progressively pinch off new segments/somites sequentially from the undifferentiated cellular mass farther towards the tail until the final total of 30-34 are formed.
The blue box is the region where somites are still forming. What I did in the movie was to zoom into just that area and watch the process as it occurred, and then played it back at a higher speed.
At the start of the movie, the area in the blue box looks like this:
That blue arrow marks the position of the last formed somite boundary. Everything to the left is nicely blocked off into a series of somites (which are more clearly seen in this closeup). Everything to the right is relatively undifferentiated mesoderm.
40 minutes later, another somite boundary is formed (green arrow).
And 40 minutes later still, another boundary forms (red arrow).
Note that this movie shows a process that’s going on a little more slowly than you’ll find in the standard staging series for the zebrafish. The staging series is defined for 28.5°C, which is the temperature the animals prefer, and at that temperature they make a new somite every 20-30 minutes. This movie was made at room temperature, a little cooler than the standard, and development was concomitantly slowed.
Dave Eaton says
Golly, that’s neat! And the related movie, the annotated embryo developing…amazing.
That is sweet. I couldn’t used that when I taught developmental bio…
That was very cool…
Do you know what (genetic/ hormonal/ other?) factors are present in guiding the formation?
Er… ‘VE. Could’VE.
PZ Myers says
Yes, my August column is all about vertebrate segmentation. This is a movie that just provides a visual for the process. (Man, it’s hard to explain what this looks like and what genetic mechanisms are responsible for it in a 1200 word limit!)
Stephen Wells says
See, that means creationism is superior, ’cause you can fit “God did it” into three words…
Wow! Zebrafish development is so awesome. Thanks for sharing, PZ.
Blake Stacey, OM says
I’m looking forward to the column itself. More such writing requires (and deserves) visual aids!
What was the equipment used to make the movie? I’ve been tempted by those big toylike microscopes with USB connections, seen in the kids’ science section of various stores.
But maybe this is something better, and more expensive?
Martin Wisse says
Completely offtopic, but speaking of videos, wait till you see what Dutch fundies have done to David Attenborough’s Life with Mammals. If you guessed “censored it to remove any and all mentions oe evolution”, go to the head of the class…
Hey PZ, would it be possible for you to write about the new discovery of a gene in fruit flies that appears to have no ancestors. I know that it will soon pop up in creationist literature.
Here’s a couple of similar movies from zebrafish that I made a few years back of the same process where I have fluorescently labeled cell nuclei. They’re not the best movies – a little blurry (they didn’t get “youtube-ized” very well) and in the first one you can see in the middle where I re-adjusted the exposure.
Peter Ashby says
Well Jeff the article you site gives you a most plausible mechanism for the formation of this gene and the information that each exon is associated with transposon sequences certainly seems to make that the most parsimonious explanation. No god required of course, just a gene that is almost the definition of a selfish one. Proof that random ‘selfish’ gene replication can be creative.
Of course that is not the only way apparently novel genes can make their way into genomes. Lateral transfer of genes, often via parasitic or viral intermediates is surprisingly common. I was once trying to clone a chicken version of a gene, i threw a group of clones at the sequencer and asked the online database to Identify the sequences, one had only two hits, one was Homo sapiens, the other was Anopheles gambiae (the malaria mosquito). Now at the time the database had the mouse genome on it, the fly genome was there too as well as a number of others and bits of lots. So we have two species who live in close proximity and a vector that feeds on both. Unfortunately it was not what I was looking for and time and cost etc considerations meant it went in the bin. But it shows how easy it is to find such things, even when you are not looking for them.
Jeff…I’ll write Dembski’s blurb on the paper, so he doesn’t have to…
“This, of course, is exactly what ID predicts. An infinitely creative and powerful Designer is not limited to re-using the same sequences over and over again in the same lineages. We eagerly await the second such discovery”.