development
pharyngula | October 14, 2008
How can I respond to a story about zebrafish, development, and new imaging and visualization techniques? Total incoherent nerdgasm is how.
Keller et al. are using a technique called digital scanned laser light sheet fluorescence microscopy (DSLM) to do fast, high-resolution, 3-D scans through developing embryos over time; using a GFP-histone fusion protein marker, they localize the nucleus of every single cell in the embryo. Some of the geeky specs:
1500x1500 pixel 2-D resolution
12 bits per pixel dynamic range
Imaging speed of 10 million voxels per second
Complete scan of a 1 cubic…
pharyngula | August 30, 2008
Wow…so have you heard about this result?
One goal of regenerative medicine is to instructively convert adult cells into other cell types for tissue repair and regeneration. Although isolated examples of adult cell reprogramming are known, there is no general understanding of how to turn one cell type into another in a controlled manner. Here, using a strategy of re-expressing key developmental regulators in vivo, we identify a specific combination of three transcription factors (Ngn3 (also known as Neurog3) Pdx1 and Mafa) that reprograms differentiated pancreatic exocrine cells in adult mice…
pzminion | August 11, 2008Monday morning, PST: time for some science with a side of controversy, Danio-style
There's a Department of Health and Human Services document circulating that's got the pro-choice lobby up in arms. Afarensis and The Questionable Authority weighed in on the sociopolitical impact of such a policy last week, but in addition to the significant threat to reproductive rights that it presents, this proposal is yet another example of the complete lack of scientific expertise informing decisions about public health.
At issue is the determination of a time point that marks the beginning of pregnancy…
purepedantry | August 7, 2008Yet another piece of evidence for the futility of abstinence education. Masters et al., publishing in the journal Perspectives on Sexual and Reproductive Health, show that an adolescent's attitude about sex is a much stronger indicator that they will actually have it than their attitudes about abstinence.
The study followed around 300 teenagers from Seattle over a year after interviewing them about their attitudes about sex and abstinence and their intentions to have sex or abstain. They wanted to know how their initial attitudes and intentions about sex and abstinence interacted over time…
pharyngula | August 1, 2008Every time I mention this developmentally significant molecule, Sonic hedgehog, I get a volley of questions about whether it is really called that, what it does, and why it keeps cropping up in articles about everything from snake fangs to mouse penises to whale fins to worm brains. The time seems appropriate to give a brief introduction to the hedgehog family of signaling molecules.
First, a brief overview of what Sonic hedgehog, or shh, is, which will also give you an idea about why it keeps coming up in these development papers. We often compare the genome to a toolbox — a collection of…
pharyngula | July 31, 2008
Ontogenetic allometry in the fang in the front-fanged Causus rhombeatus (Viperidae) displaces the fang along the upper jaw. Scale bars, 1 mm. We note the change in relative size of the upper jaw subregions: i, anterior; ii, fang; iii, posterior. d.a.o., days after oviposition.
I keep saying this to everyone: if you want to understand the origin of novel morphological features in multicellular organisms, you have to look at their development. "Everything is the way it is because of how it got that way," as D'Arcy Thompson said, so comprehending the ontogeny of form is absolutely critical to…
pharyngula | July 23, 2008
Life has two contradictory properties that any theory explaining its origin must encompass: similarities everywhere, and differences separating species. So far, the only theory that covers both beautifully and explains how one is the consequence of the other is evolution. Common descent unites all life on earth, while evolution itself is about constant change; similarities are rooted in our shared ancestry, while differences arise as lineages diverge.
Now here's a new example of both phenomena: the development of segmentation in snakes. We humans have 33 vertebrae, zebrafish have 30-33,…
pharyngula | July 22, 2008
Epigenetics is the study of heritable traits that are not dependent on the primary sequence of DNA. That's a short, simple definition, and it's also largely unsatisfactory. For one, the inclusion of the word "heritable" excludes some significant players — the differentiation of neurons requires major epigenetic shaping, but these cells have undergone a terminal division and will never divide again — but at the same time, the heritability of traits that aren't defined by the primary sequence is probably the first thing that comes to mind in any discussion of epigenetics. Another problem is…
pharyngula | July 19, 2008Massimo Pigliucci has posted the notes, parts 1, 2, and 3, from the Altenberg meeting that was unfortunately over-hyped by the creationist crowd (no blame for that attaches to the organizers of this meeting). It sounds like it was a phenomenally interesting meeting that was full of interesting ideas, but from these notes, it was also clearly a rather speculative meeting — not one that was trying to consolidate a body of solid observations into a coherent explanation, but one that was instead trying to define promising directions for an expansion of evolutionary theory. That's also the message…
pharyngula | July 19, 2008Teratology is so interesting — it gives us hints about the mechanisms driving developmental processes. In some cases, when you just have a few isolated instances, it can be frustrating, because there isn't enough information to go much beyond speculation. Here's one of those tantalizing cases: an octopus with branching tentacles.
Now that is fascinating. Look at limb formation as an abstract developmental problem in which you first have to initiate a protrusion from a specific place on the body wall; the protrusion has to elongate to a specific length; and it has to be patterned along its…
pharyngula | July 16, 2008I'm on my way home, and am actually using a fast internet connection at the airport — I'd forgotten what it was like! I quickly uploaded a few essential files, and my mail software is downloading my email. Unfortunately, I'd need a really fast connection to handle all that — the number of messages pouring in might actually hit 5 digits. If you're hoping for a reply to anything, you might well be out of luck here.
Atlanta has been very pleasant, with friendly people and good company. I'll have to come back sometime. The meeting itself was challenging for a mere biologist, but I might have…
pharyngula | July 5, 2008Remember Suzan Mazur, the credulous reporter hyping a revolution in evolution? She's at it again, publishing an e-book chapter by chapter on the "Altenberg 16", this meeting that she thinks is all about radically revising evolutionary biology.
I can tell that Massimo Pigliucci — one of the 16 — is feeling a little exasperation at this nonsense, especially since some of the IDists have seized on it as vindication of their delusions about the "weakness" of evolutionary theory. He's got an excellent post summarizing some of the motivation behind this meeting, which is actually part of a fairly…
pharyngula | June 26, 2008
This is an amphioxus, a cephalochordate or lancelet. It's been stained to increase contrast; in life, they are pale, almost transparent.
It looks rather fish-like, or rather, much like a larval fish, with it's repeated blocks of muscle arranged along a stream-lined form, and a notochord, or elastic rod that forms a central axis for efficient lateral motion of the tail…and it has a true tail that extends beyond the anus. Look closely at the front end, though: this is no vertebrate.
It's not much of a head. The notochord extends all the way to the front of the animal (in us vertebrates, it…
zooillogix | June 4, 2008A fascinating article in Livescience reveals the answer to a century-old zoological mystery: what do y-larvae grow up to become? Discovered in 1899, y-larvae are clearly young crustaceans but their adult stage could not be determined. While this in itself was perplexing, the newly discovered answer is even more startling: y-larvae metamorphosize into "simple, pulsing, slug-like masses of cells... far simpler than their larval stage." In a sense, the creatures revert backwards to forms more commonly seen further down the evolutionary ladder as they mature.
Watch the process
This awesome video…
pharyngula | May 29, 2008I've discovered a couple of important things at this meeting.
One, late night sessions at west coast meetings are deadly for any of us coming from more eastern time zones. At least the morning sessions are low stress.
Two, I haven't heard one Drosophila talk yet, and the message is clear: we're now in the stage of evo-devo in which everyone is diversifying and chasing down a wide array of species. There was a bit of model-system bashing, but at the same time, everyone is acknowledging the crucial role of those traditional, but weird and derived, lab critters in providing a point of comparison…
gregladen | May 19, 2008Quirky Pulsar System Challenges Theories of Binary Formation; Observing Stem Cells at Work; Large scale carbon sequestration
Quirky Pulsar System Challenges Theories of Binary Formation
From a Cornell Press Release:
An ongoing sky survey using the Cornell-managed Arecibo radio telescope in Puerto Rico has turned up a massive, fast-spinning binary pulsar with a mysterious elongated orbit, researchers say.
The pulsar and its companion star challenge currently accepted views of binary pulsar formation and give researchers a new opportunity for understanding the fundamental properties of highly…
pharyngula | May 18, 2008You may recall that a while back I mentioned how Jerry Coyne praised some work on bat evo-devo. I also said that I was going to have to write that paper up sometime. The bad news: I haven't written it up for the blog. The good news: I did write it up for a future Seed column. The better news: Stephen Matheson has a summary right now, so you don't have to wait for my column to come out.
You should still subscribe anyway. It's pretty on shiny paper.
pharyngula | April 14, 2008Jay Hosler has a new book out, Optical Allusions(amzn/b&n/abe/pwll). If you're familiar with his other books, Clan Apis(amzn/b&n/abe/pwll) and The Sandwalk Adventures(amzn/b&n/abe/pwll), you know what to expect: a comic book that takes its science seriously. Hosler has a fabulous knack for building serious content into a light and humorous medium, just the kind of approach we need to get wider distribution of science into the culture.
This one has a strange premise. Wrinkles the Wonder Brain is an animated, naked brain working for the Graeae Sisters, and he loses the one eye they…
pharyngula | April 6, 2008[Since I had to fly away early this morning and missed all these talks, I had to rely on regular commenter DanioPhD to fill in the gaps … so here's her summary:]
This morning's final series of talks each focused on a different phylum, but the unifying theme was one of bridging the processes of microevolution and macroevolution. The first talk after breakfast (and a long night of Scotch-drinkin' and story-swappin' prior to that) was Bernie Degnan of the University of Queensland. He summarized his work on Amphimedon queenslandica, a sponge species developed as a model of a representative…
pharyngula | April 5, 2008I'm going to get off a quick summary of this afternoon's talks, then I have to run down to the poster session to find out what the grad students have been doing. Are we having fun yet? I'm going to collapse in bed tonight, and then unfortunately I have to catch an early flight back home, so I'm going to miss a lot of cool stuff tomorrow.
First up after lunch was Deneen Wellik, who summarized her work with Hox genes and patterning the vertebrate axial skeleton. I'm spared some effort here — I already wrote up her paper, so read that for the whole story. In short, one of the confounding things…