What I taught in the development lab today

After our disastrous chick lab — it turns out that getting fertilized chicken eggs shipped to remote Morris, Minnesota during a blizzard is a formula for generating dead embryos — the final developmental biology lab for the semester is an easy one. I lectured the students on structuralism and how there are more to cells then genes (there’s also cytoplasm and membranes and environment) earlier today. This afternnon I’ve given them recipes for soap bubble solution and told them to play. They’re supposedly making little model multicellular organisms by chaining soap bubbles together, and observing how the membranes follow rules of organization just like the ones we see in living tissue.

In case you’re wondering what the recipe is so you can do it too, here’s my bubble soap formula:

  • 5ml Dawn dishwashing soap

  • 100ml DI water

  • 1ml glycerine

It gets better as it ages — there are perfumes and a small amount of alcohol solvent in the dishwashing liquid which evaporate off with time. The students are playing with concentrations, and if you’re making it up fresh and don’t want to wait until tomorrow, you can increase the concentrations of soap and glycerine.

The more glycerine you add, the more long-lasting the bubbles are…and unfortunately, the heavier they are. If you want bubbles that will waft gently on the breeze, you’ll want less glycerine. It’s a very forgiving recipe, just play.

I’ve also provided the students with a couple of books: the classic Soap Bubbles: Their Colors and Forces Which Mold Them by C.V. Boys, and The Science of Soap Films and Soap Bubbles by Cyril Isenberg. They’re more about math and physics, but they have some nice illustrations. These are projects you can do at home with cheap ingredients bought at the grocery store, so those of you with kids might try playing with it this summer. There are simple rules about the angles of intersection between bubbles — if you’re mathematically inclined, take pictures and use a protractor and see if you can work them out. There’s also some really cool stuff going on with colors, since the bubbles have a gradient of thickness from top to bottom and you get wonderful colors caused by refraction and reflection and phase shifts across the membrane.

OK, if you don’t have kids, you have my permission to play with soap bubbles, too. Tell everyone who looks at you funny that you’re doing Science!

What I taught today: a send-off with an assignment

Today was the last day I lecture at my developmental biology students. We have one more lab and one final class hour which will be all about assessment, but this was my last chance to pontificate at them…so I told them about all the things I didn’t teach them, and gave them a reading list for the summer. (I know, there’s no way they’re going to take these to the beach, but maybe when they move on in their careers they’ll remember that little reference in their notes and look it up.)

So here are the books I told them to go read.

We’ve been all up in the evo-devo house this semester, so I urged them to read the antidote, just to get some perspective. This is the great big book all the grown-up developmental biologists read and admire and regard as gloriously wrong in many ways, but still an important reminder that physical and chemical properties of whole cells and organisms matter — it’s not all genes. And of course that legendary book is On Growth and Form by D’Arcy Wentworth Thompson. I tell all my students that if ever they want to get serious about developmental biology, they must read Thompson.

For the more modern gang who like computers and math and logic puzzles, I point them at At Home in the Universe: The Search for the Laws of Self-Organization and Complexity and The Origins of Order: Self-Organization and Selection in Evolution by Stuart A. Kauffman. He’d really benefit from more time in a wet lab, but still, there’s some very provocative stuff in those books about how complexity can spontaneously arise. I also gave them a bit of an introduction to NK network theory.

There is always a philosopher or two in the class, so for them I suggest that they read The Ontogeny of Information: Developmental Systems and Evolution by Susan Oyama. Developmental Systems Theory suffers for its lack of applicability — it really is a little too abstract for most scientists — but I love it for its more holistic approach to development.

For the hardcore biologists, the ones who are ready to read a book where every page makes them think very hard, I suggest Developmental Plasticity and Evolution by Mary Jane West-Eberhard. It’s quite possibly the most brilliant book I’ve ever read, but it’s dense and challenging. Intentionally challenging: she really does question a lot of the dogma of evolutionary and developmental biology, and forces you to realize there are a lot of wide-open, intensely interesting questions out there.

And finally, I brought up a book I seriously think about making the class text every year, Ecological Developmental Biology by Scott F. Gilbert and David Epel. The course as it is now is a fairly traditional modern molecular genetics and development class, with a solid overlay of evolutionary biology. The Gilbert and Epel book integrates all that with ecology — and I firmly believe that the well-rounded biologist of the type a liberal arts university tries to generate ought to have a balanced conceptual understanding of ecology, development, and evolution.

That’s the short list. It’s too bad I don’t have total control of my students’ lives, or I’d have them studying ten or twenty books over the summer. Or they probably think it’s a good thing I don’t.

It’s another exam day!

I’ve been terrible about updating everyone about my class the last few weeks — we’re coming up on the end of the semester, so I’ve been going a little bit mad. We’ve been focusing on vertebrate development lately, and right now we’ve got a few dozen fertilized chicken eggs sitting in an incubator and developing embryos. Maybe. It is always a real pain to get these things delivered to remote Morris, Minnesota — I delayed this part of the lab to the very end of the semester, hoping the sun would emerge and warm the hemisphere enough that when UPS took their sweet time getting them to me, they wouldn’t freeze in the back of the truck. As usual, though, next day delivery turned into two day delivery, and we haven’t seen Spring yet. So we’ll soon know whether they survived their harrowing journey through the frigid Northlands, and if they haven’t, I’ll have to throw up my hands and cry.

Or I could torture my students to ease my frustration. Yeah, that’s the ticket. So it’s exam day.

Developmental Biology Exam #3

This is a take-home exam. You are free and even encouraged to discuss these questions with your fellow students, but please write your answers independently — I want to hear your voice in your essays. Also note that you are UMM students, and so I have the highest expectations for the quality of your writing, and I will be grading you on grammar and spelling and clarity of expression as well as the content of your essays and your understanding of the concepts.

Answer two of the following three questions, 500-1000 words each. Do not retype the questions into your essay; if I can’t tell which one you’re answering from the story you’re telling, you’re doing it wrong. Include a word count in the top right corner of each of the two essays, and your name in the top left corner of each page. This assignment is due in class on Monday, and there will be a penalty for late submissions.

Question 1: One of Sarah Palin’s notorious gaffes was her dismissal of “fruit fly research” — she thought it was absurd that the government actually funded science on flies. How would you explain to a congressman that basic research is important? I’m going to put two constraints on your answer: 1) It has to be comprehensible to Michele Bachmann, and 2) don’t take the shortcut of promising that which you may not deliver. That is, no “maybe it will cure cancer!” claims, but focus instead on why we should appreciate deeper knowledge of biology.

Question 2: There is an interesting tension in evo devo: on the one hand, we like to talk about the universality of molecular mechanisms, but on the other hand, we’re also very interested in the differences, both in phenotype and genetics. This is an old debate in evolutionary theory, too, so it’s not unique to development, but how do you reconcile unity and diversity simultaneously?

Question 3: When I told you about axis specification in Drosophila, the story was relatively straightforward: maternal factors switch on a chain of zygotic genes that set up the pattern. When I told you about the same process in vertebrates, though, I didn’t give you the same level of detail—I gave you buckets of transcription factors and said they had various roles. Dig deeper. Pick ONE of these vertebrate dorsalizing factors out of the bucket and tell me more about it: noggin, chordin, frizbee, goosecoid, pintallavis.

My ulterior motive

In case you’re wondering why I’m experimenting with video, there actually is an ulterior motive, and it’s the same one that got me into blogging in the first place: teaching. I’m teaching science at an undergraduate institution, and contrary to many people’s expectations, a bachelor’s degree does not confer a deep understanding of science, and it can’t. Students come out of high school with an ability to read and do basic math (at least the ones we admit to college!), and have wildly varying abilities in writing, analysis, and thinking. I think the undergraduate university’s role is more to deepen the student’s abilities in those general skills, and also to provide a broad knowledge base in a discipline of their choosing. We’re preparing students to go off and do science, if that’s what they want to do. I’ve done my job if my students go to graduate school competent and confident, ready to get to work and explore the natural world. Or if they choose not to follow a science career, they’re open to read and think about the world in a scientific way.

So there are a couple of things I do in my upper level lab courses. I take a hands-off approach: I teach students how to use the tools in my lab, give them a general idea of what would be cool to do or see, and turn them loose. If I see a combination of frustration (“I can’t get it to work! How do I get it to work?”) and play (“What if we do this?”), it’s a success. I have them blogging because it’s a sneaky way to get them to think about the subject of the class outside of class, and also to get them to blend their interests — which usually aren’t identical to mine! — with what I’m teaching.

And then there are presentations. Communicating your work is an important part of doing science, too. I try to get them to do that with the blogging, but also our university promotes a capstone experience, our senior seminars. Before a student can graduate, they have to do a one hour talk on some subject in their discipline, and it’s a big deal/ordeal to the students, and also a big deal/ordeal for us faculty in one of the largest majors on campus. Their quality varies all over the place, even though many of my colleagues and I do incorporate requirements for giving in-class presentations in our upper level courses, and we have a preparatory course on writing that includes giving presentations. There’s a limitation on doing that in class, though: you’ve got 20 students, you can’t chew up multiple class hours getting them all to do rehearsals and rehearsals under your supervision. We usually get an abstract and a promise and a conversation with them to help explain the data, and then boom, they do their talk to the class. It’s one shot and they’re done. That’s not the way to learn.

So I’ve had this idea…this is a generation that’s comfortable with their camera phones, that whiles away hours on facebook and youtube. What if I tried to combine that with doing presentations? What if, in one of my lab courses, I made the final project to be producing a short youtube video explaining some piece of data that they’d gotten in the lab? Put a micrograph or a chart or a time-lapse video on the screen and explain it with a voice-over, or stand in front of a camera while discussing some fine point of theory, or make a how-to video on how to use the microscope. It’s something they could tweak until it looks good, I’d be able to review work in progress fairly easily, and then what they put up for final evaluation might be a little more polished. This would be a useful skill for the future. I’m also rather impressed with how Casey Dunn has his students make creature features.

One catch: to have the students do it, I have to be able to do it. So in my spare time (hah!), I’ve been tinkering with ideas. I got some clamp lamps to play with lighting, I’ve got some cheap and simple backdrops to play with, I read Steve Stockman’s How to Shoot Video That Doesn’t Suck (which has a lot of damn good basic practical advice), and I’ve been doing some experimenting, most of which will never see the light of day. I’m learning stuff, which is always fun.

And it’s useful stuff, too. For instance, I’m a words and typing sort of guy, so my approach so far has been to write a script and then wrap video and images around it. That doesn’t work so well. I’m slowly learning that in this medium you start with video and images and wrap words around them. And that’s exactly what we do routinely in a science talk! You’ve got these chunks of data in the form of images and numbers, and what you do in a presentation is show them and add your verbal explanation on top. Man, I ought to know this stuff already. I just have to adapt.

So this summer you might be seeing more of my unphotogenic face in videos as I clumsily try to get some basic skills in this medium. The payoff, though, is that in a year or so I’ll be able to teach my students how to do it better, and then we’ll get a fine new crop of video stars who are comfortable explaining science in front of a camera.

But don’t worry, you don’t have to suffer through my struggles, just don’t watch me.

What I taught today: O Cruel Taskmaster!

I’m out of town! Class is canceled today! But still, my cold grip extends across the Cascades, over the Palouse, the Rockies, the Dakota badlands, the old homeland of the American bison, the the great farms of the midwestern heartland, to a small town in western Minnesota, where I crack the whip over a tiny group of hardworking students. They’ve been mastering the basics of timelapse video microscopy in the lab this week, I hope, and will be showing me the fruits of their labors on Monday. I’m also inflicting yet another exam on them over the weekend. Here are the questions they are expected to address.

Developmental Biology Exam #2

This is a take-home exam. You are free and even encouraged to discuss these questions with your fellow students, but please write your answers independently — I want to hear your voice in your essays. Also note that you are UMM students, and so I have the highest expectations for the quality of your writing, and I will be grading you on grammar and spelling and clarity of expression as well as the content of your essays and your understanding of the concepts.

Answer two of the following three questions, 500-1000 words each. Do not retype the questions into your essay; if I can’t tell which one you’re answering from the story you’re telling, you’re doing it wrong. Include a word count in the top right corner of each of the two essays, and your name in the top left corner of each page. This assignment is due in class on Monday, and there will be a penalty for late submissions.

Question 1: One of the claims of evo devo is that mutations in the regulatory regions of genes are more important in the evolution of form in multicellular organisms than mutations in the coding regions of genes. We’ve discussed examples of both kinds of mutations, but that’s a quantitative claim that won’t be settled by dueling anecdotes. Pretend you’ve been given a huge budget by NSF to test the idea, and design an evodevo research program that would resolve the issue for some specific set of species.

Question 2: Every generation seems to describe the role of genes with a metaphor comparing it to some other technology: it’s a factory for making proteins, or it’s a blueprint, or it’s a recipe. Carroll’s book, Endless Forms Most Beautiful, describes the toolbox genes in terms of “genetic circuitry”, “boolean logic”, “switches and logic gates” — he’s clearly using modern computer technology as his metaphor of choice. Summarize how the genome works using this metaphor, as he does. However, also be aware that it is a metaphor, and no metaphor is perfect: tell me how it might mislead us, too.

Question 3: We went over the experiment to test the role of enhancers of the Prx1 locus which showed their role in regulating limb length in bats and mice. Explain it again, going over the details of the experiment, the results, and the interpretation…but without using any scientific jargon. If you do use any jargon (like “locus”, “regulation”, “enhancer”), you must also define it in simple English. Make the story comprehensible to a non-biologist!

Yeah, you don’t have to tell me. I’m evil.

What I taught today: those oddball critters, the vertebrates

We’ve been talking about flies nonstop for the last month — it’s been nothing but developmental genetics and epistasis and gene regulation in weird ol’ Drosophila — so I’m changing things up a bit, starting today. We talked about vertebrates in a general way, giving an overview of major landmarks in embryology, and a little historical perspective.

We take a very bottom-up approach to studying fly development: typically, fly freaks start with genes, modifying and mutating them and then looking at phenotype. Historically, vertebrate embryology goes the other way, starting with variations in the phenotype and inferring mechanisms (this has been changing for the last decade or two; we often start with a gene, sometimes from a fly, and use that as a probe to hook into the genetic mechanisms driving developmental processes). What that means is the 19th and early 20th century literature on embryology is often comparative morphology, looking at different species or different stages and trying to extract the commonalities or differences, or it’s experimental morphology, making modifications (usually not genetic) to the embryo and asking what happens next. Genes were not hot topics of discussion until the last half of the 20th century, and even then it took a few decades for the tools to percolate into the developmental biologists’ armory.

And much of 19th century embryology went lurching down a dead end. We talked about Haeckel, the grand sidetracker of the age. There was a deep desire to integrate development and evolution, but they lacked the necessary bridge of genetics, so Haeckel borrowed one, his theory of ontogenetic recapitulation. A theory that quickly went down in flames in the scientific community (jebus, Karl Ernst von Baer had eviscerated it 50 years before Haeckel resurrected it). We actually spent a fair amount of class time going over arguments for and against, and modern interpretations of phylotypy — it isn’t recapitulation, it’s convergence on a conserved network of global spatial genes that define the rough outlines of the vertebrate body plan.

Finally, I gave them a whirlwind tour of basic developmental stages of a few common vertebrate models: frog, fish, chick, and mouse. We’re going to talk quite a bit about early axis specification events in vertebrates (next week), and gastrulation (probably the week after), so I had to introduce them to the essential terminology and events. I think they can see the fundamental morphological events now — next, β-catenin and nodal and Nieuwkoop centers and all that fun stuff!

(Today’s slides (pdf))

What I taught today: molecular biology of bat wings

Hard to believe, I know, but this class actually hangs together and has a plan. A while back, we talked about the whole cis vs. trans debate, and on Monday we went through another prolonged exercise in epistatic analysis in which the students wondered why we don’t just do genetic engineering and sequence analysis to figure out how things work, so today we reviewed a primary research paper by Chris Cretekos (pdf) that teased apart the role of one regulatory element to one gene, Prx1, in modifying the length of limbs. It’s a cool paper, you should read it. It’s kind of hard to replicate the teaching experience in a blog post, though, because what I did most of the hour was ask questions and coax the students into explaining methods and figures and charts.

I’m afraid that what you’re going to have to do is apply for admission to UMM, register for classes, and take one of my upper level courses. I always have students read papers direct from the scientific literature, and then I torture them with questions until they extract meaning from them. It’s fun!

Although…it would also be cool to have a scientific-paper reading and analysis session at a conference, now wouldn’t it? Especially if it could be done over beer.

What I taught today: farewell to flies (for a while)

A good portion of what I’ve been teaching so far uses Drosophila as a model system — it’s the baseline for modern molecular genetics. Unfortunately, it’s also a really weird animal: highly derived, specialized for rapid, robust development, and as we’ve learned more about it, it seems it has been layering on more and more levels of control of patterning. The ancestral system of establishing the body plan was far simpler, and evolution has worked in its clumsy, chance-driven way to pile up and repurpose molecular patterning mechanisms to reinforce the reliability of development. So I promised the students that this would be the last day I talk about insects for a while…we’ll switch to vertebrates so they can get a better picture of a simpler, primitive system. What we’ll see is many familiar genes from flies, used in some different (but related!) ways in vertebrates.

But today I continued the theme of epistatic interactions from last week. Previously, we’d talked about gap genes — genes that were expressed in a handful of broad stripes in the early embryo, and which were regulated in part by the even broader gradient of bicoid expression. The next level of the hierarchy are the pair rule genes, which are expressed in alternating stripes — 7 pairs of stripes for 14 segments.

First point: notice that we are seeing a hierarchy, a descending pattern of regulatory control, and that the outcome of the hierarchy is increasing complexity. One gene, bicoid sets up a gradient that allows cells to sense position by reading the concentration of the gene; the next step leverages that gradient to create multiple broad domains; and the pair rule genes read concentrations of gap genes and uses the boundaries between them to set up even more, smaller and more precise domains of stripes that establish the animal’s segments.

This is epigenesis made obvious. The 14 stripes of the pair rule genes are not present in the oocyte; they emerge via patterns of interactions between cells and genes. The information present in the embryo, as measured by the precise and reproducible arrays of cells expressing specific genes, increases over time.

So part of the story is hierarchy, where a complex pattern at one stage is dependent on its antecedents. But another part of the story is peer interaction. Cells are inheriting potentials that are established by a cascading sequence of regulatory events, but in addition, genes at the same approximate level of the hierarchy are repressing and activating each other. We can tease those interactions apart by fairly straightforward experiments in which we knock out individual pair rule genes and ask what the effect of the loss has on other pair rule genes. I led the students through a series of epistatic experiments which started out fairly easy. Knock out a pair rule gene that is expressed in odd numbered parasegments, for instance, and it’s complement, the pair rule gene expressed in even parasegments, expands its expression pattern to fill all segments. Sometimes.

Some of the experiments reveal simple relationships: hairy suppresses runt, and runt suppresses hairy. That makes sense. They have mutually exclusive domains, so it’s no surprise that they exclude each other. But then we looked at other pair rule genes which are expressed in patterns slightly out of phase from the hairy/runt pair, and there the relationships start getting complex. Genes like fushi tarazu are downstream from all the others, and their effects are straightforward (their loss doesn’t disrupt the other pair rule genes), but genes like even-skipped have much messier relationships, and the class was stumped to explain the results we get with that deletion.

So I asked them to come up with other experiments to tease apart these interactions. I was somewhat amused: when I think along those lines, I come up with more genetic crosses and analyses of expression patterns — I think about regulatory logic and inferring rules from modifications of the pattern. Students nowadays…they’re so much more direct. They want to go straight to the molecular biology, taking apart the genes, identifying control elements, building reporter constructs to see gene-by-gene effects. I felt so old-fashioned. But we also had to talk about the difficulty of those kinds of experiments, and that often the genetic approach is better for building a general hypothesis that can be fruitfully tested with the molecular approach.

Then we stopped — we’ll come back to flies later, and start looking at some specific subsets of developmental programs. Next, though, we’re going to take a big step backward and look at early events in vertebrates and progress through that phylum until we see how they build segments. I’m hoping the students will see the similarities and differences.

Slides for this talk (pdf)

What I taught today: heavy on the epistasis

Today we talked about gap genes and a little bit about pair rule genes in flies, and to introduce the topic I summarized genetic epistasis. Epistasis is a fancy word for the interactions between genes, and we’ve already discussed it on the simplest level. You can imagine that a gene A, when expressed, activates the expression of gene B. The arrow in this diagram? That’s epistasis.

epi1

So far, so simple. This could describe how bicoid activates zygotic hunchback for instance. But of course not all epistatic interactions are linear and one dimensional; often one transcription factor will turn on or repress multiple genes — so A might switch on genes B, C, and D.

epi2

But wait! Now there is the potential for all kinds of combinatorial interactions: maybe C has positive feedback back on A, and B activates D and C, and D activates B, and C represses B. There’s a whole mathematically bewildering world of possibility here.

epi3

And it gets worse and worse. B, C, and D could have downstream effects on other genes, like E, F, G, and H, and each of those interact with each other and can have feedback effects as well. It’s not at all uncommon to be taking apart the sequence of events of a developmental pathway and discover a whole tangled snarl of epistatic interactions that lead to complicated patterns of gene expression.

epi4

And that’s molecular geneticists and developmental biologists do: they try to tease apart the snarl, asking how each gene interacts with all the other genes in the system, working out the kind of genetic circuitry shown in those diagrams. Often the approach is take it one gene at a time: knock out F, for instance, and ask what happens to the expression patterns of A, B, C, D, E, G, and H. Or upregulate D, and ask what all those other genes do. If you like logic puzzles, you’ll love epistatic studies, because that’s what they are: grand complicated logic puzzles with multiple cascading effects and usually only partial knowledge about what each component does. You’ll either have great fun with it all, or cultivate great headaches.

So most of the class hour was spent going through examples of these puzzles. The gap genes, for instance, are expressed in broad stripes in the embryo, and we can try to decipher the rules that establish the boundaries by taking out components. If hunchback is deleted, what do the giant, krüppel, and knirps stripes look like? Take out krüppel, what happens to knirps? So I led them through this series of experiments, asking them to come up with general rules regulating the expression of each stripe, and then using those rules to predict what would happen if we did a different experiment. I think they mostly got it.

But of course the discussion today was mostly about the gap genes, which are the second tier of genetic interactions (analogous to my third figure above). Next I introduced the pair rule genes, the third tier, rather like my fourth diagram. These are genes that are expressed in alternating stripes corresponding to parasegments in the fly…so we’ve gone from a few broad stripes to many narrow stripes. Each of those stripes, too, is independently regulated, with distinct control regions for each.

The real nightmare begins in the next class, when we start taking apart the many ways all of the pair rule genes interact with each other, and how their position is established partly by regulation by the gap genes and partly by mutual sorting out with combinations of activating and repressing interactions. It’s going to be loads of fun!

Today’s slides.

A little blogging exercise for my students

In my development class, students have been blogging away for the last few weeks, and I asked them to send me links to ones they wouldn’t mind seeing advertised. I’ve told them that an important part of effectively blogging is to link and comment, so they’re supposed to write something this week that adds to one of these posts and links to it on their own blog, and they’re also supposed to leave a comment on their fellow students’ work.

I warned them too that I’d highlight these publicly and urge my readers to look and say a few things: so go ahead and comment, criticize, praise, whatever — I told them that the good will come with the bad.

I suspect I’ll have to explain to them how to kill spam and remove irrelevant or outrageous comments in the next class…